annual report for the norwegian national seismic network 2016

Annual report for the

Norwegian National Seismic Network

2016

Supported by

University of Bergen

and

Norwegian Oil and Gas Association

Prepared by

Department of Earth Science

University of Bergen

Allegaten 41, N-5007 Bergen

March 2017

CONTENTS

1 Introduction ......................................................................................................................... 1 2 Operation ............................................................................................................................. 1

2.1 NNSN .......................................................................................................................... 1 2.2 NNSN field stations maintenance ................................................................................ 5 2.3 The NORSAR stations and arrays ............................................................................... 8

3 NNSN achievements and plans ......................................................................................... 13 3.1 NNSN achievements in 2016 .................................................................................... 13

3.2 NNSN plans for 2017 ................................................................................................ 13 3.3 Projects related to NNSN .......................................................................................... 14

4 Seismicity of Norway and surrounding areas for 2016 .................................................... 16 4.1 Velocity models and magnitude relations ................................................................. 17 4.2 Events recorded by the NNSN ................................................................................... 19

4.3 The seismicity of Norway and adjacent areas ........................................................... 22 5 Scientific studies ............................................................................................................... 42

5.1 QLg tomography........................................................................................................ 42 5.2 Relocation of seismicity in southern Norway and the North Sea using a Bayesian

hierarchical multiple event location algorithm ..................................................................... 43 5.3 Testing of a method for distinguishing between earthquakes and explosions .......... 45

5.4 Towards the integration of NNSN stations in automatic network event location ..... 47 6 Publications and presentations of NNSN data during 2016 .............................................. 48

6.1 Publications ............................................................................................................... 49 6.1 Master degree thesis, UiB .......................................................................................... 49 6.2 Oral presentations ...................................................................................................... 49

6.3 Poster presentations ................................................................................................... 51

7 References ......................................................................................................................... 51

Seismicity of Norway, January – December 2016 Department of Earth Science, UiB

1

1 Introduction

This annual report for the Norwegian National Seismic Network (NNSN) covers operational

aspects for the seismic stations contributing data, presents the seismic activity in the target

areas and the associated scientific work carried out under the project. The report is prepared

by the University of Bergen with contributions from NORSAR.

The NNSN is supported by the oil industry through the Norwegian Oil and Gas Association

and the University of Bergen (UiB).

All the data stored in the NNSN database are available to the public via Internet, e-mail or on

manual request. The main web-portal for earthquake information is www.skjelv.no. It is

possible to search interactively for specific data and then download the data from

ftp://ftp.geo.uib.no/pub/seismo/DATA. Data are processed as soon as possible and updated

lists of events recorded by Norwegian stations are available soon after recording. These

pages are automatically updated with regular intervals.

2 Operation

2.1 NNSN

The University of Bergen (UiB) has the main responsibility to run the NNSN and operates 34

of the seismic stations that form the NNSN located as seen in Figure 1. NORSAR operates 3

seismic arrays, which also include broadband instruments, and three single seismometer

stations (JETT, JMIC and AKN).

In addition to the NNSN stations, waveform data from selected stations in Finland

(University of Helsinki), Denmark (GEUS), Sweden (University of Uppsala) and Great

Britain (BGS) are transferred in real time and included in the NNSN database. More than 20

stations located in or operated by neighbouring countries are recorded continuously in Bergen

and can be used for locating earthquakes, see Figure 1 and Figure 2. Phase data from

neighbour countries and from arrays in Russia (Apatity), Finland (Finess), Sweden (Hagfors)

are also included.

In total, NORSAR provides data from 12 broadband stations to the NNSN. One station with

real-time data is provided from the Ekofisk field by ConocoPhillips. The station HSPB is

operated jointly between NORSAR and the Geophysical Institute, Polish Academy of

Sciences, Warsaw, Poland and the stations BRBA and BRBB, both located in Barentsburg,

Svalbard, are a collaboration between NORSAR and the Kola Science Centre, Russian

Academy of Sciences, Apatity, Russia.

The seismicity detected by the network is processed at UiB, however NORSAR also integrate

their results into the joint database at UiB. At NORSAR the parameters of analyst-reviewed

events are converted into parameter files in Nordic format and forwarded via ftp to UiB on a

weekly basis. The magnitude threshold is set to about M=1.5 for regional events of potential

interest for the NNSN. After transferring the parameter files, the NORSAR analyst logs into

the UiB database using SEISAN and integrates the events. Integration means to merge

http://www.skjelv.no/

ftp://ftp.geo.uib.no/pub/seismo/DATA


2

NORSAR and UiB events, which may require to repick seismic phases, to include new phase

readings, to edit double phase readings and to relocate the seismic event with the new

parameters.

Figure 1. Stations contributing to the Norwegian National Seismic Network (NNSN). UiB operates 34

stations (red) and NORSAR operates the stations marked in blue, including the three arrays and stations

AKN and JMIC.

Seismic data recorded at stations located on Greenland and operated by GEUS are included in

the NNSN real-time processing, Figure 2. These data are important for the location of

earthquakes west of Jan Mayen and at the northern part of the Knipovich ridge to the Gakkel

ridge.


3

Figure 2. Seismic stations in the arctic area.

UiB is in the process of upgrading the NNSN by changing short period (SP) to broadband (BB)

seismometers. The current status of this upgrade is shown in Table 1. As of today the numbers of

SP, BB stations and stations with real time transmission are listed in Table 1.

Table 1. Overview of UiB seismic stations

Short Period Broadband Real time

Number of stations

7

27

(24 with natural period

greater than

100 sec)

31

(not real time are 2

short period and 1

broadband stations

on Jan Mayen)

The operational stability for each station is shown in Table 2. The down time is computed

from the amount of data that are missing from the continuous recordings at UiB. This is done

as the goal is to obtain as complete continuous data from all stations as possible. The statistics

will, therefore, also show when a single component is not working. Also, communication or


4

computing problems at the centre will contribute to the overall downtime. In the case of

communication problems, a station may not participate in the earthquake detection process,

but the data can be used when it has been transferred. Thus, the statistics given allow us to

evaluate the data availability when rerunning the earthquake detection not in real-time.

The data completeness for the majority of the stations is above 95%, except for the following

stations HYA and the three Jan Mayen stations (see technical service overview for details).

Table 2. Data completeness in % for 2016 for all stations of the NNSN operated by UiB.

Station

Data

completeness

%

Station

Data

completeness

%

Askøy (ASK) 100 Kongsberg

(KONO) 98

Bergen (BER) 100 Konsvik (KONS) 100

Bjørnøya (BJO) 96 Lofoten (LOF) 100

Blåsjø (BLS) 100 Mo i Rana

(MOR8) 99

Dombås (DOMB) 100 Molde (MOL) 99

Fauske (FAUS) 100 Namsos (NSS) 100

Florø (FOO) 97 Odda (OOD1) 99

Hammerfest

(HAMF) 100 Oslo (OSL) 100

Homborsund

(HOMB) 98 Skarslia (SKAR) 98

Hopen (HOPEN) 96 Snartemo

(SNART) 99

Høyanger (HYA) 94 Stavanger (STAV) 100

Jan Mayen (JMI) Ca. 85 Steigen (STEI) 99

Jan Mayen (JNE) Ca. 50 Stokkvågen

(STOK) 99

Jan Mayen (JNW) Ca. 50 Sulen (SUE) 99

Karmøy (KMY) 98 Blussuvoll

(TBLU) 99

Kautokeino (KTK1) 100 Tromsø (TRO) 99

Kings Bay (KBS) 98 Vadsø (VADS) 100


5

2.2 NNSN field stations maintenance

The technical changes for each seismic station are listed below. It is mentioned when these

changes are carried out by the respective local contact and not by the staff of UiB. When a

station stops working, tests are made to locate the problem. Sometimes the reason cannot be

found and the cause of the problem will be marked as unknown.

Major changes during this reporting period of 2016 were:

Ask (ASK) 12.08.16: Station inspected to find fault with seismometer east component.

03.11.16: Visit. Cable to EW component severed, a spare wire pair was used

to repair.

Bergen

(BER)

No visit or technical changes

Bjørnøya

(BJO1)

10.01.17: Communication down since 20.12.2016. Data from this time period

could not be retrieved because the filesystem on the USB memory was

corrupted. All data from this time period has been lost.

Blåsjø (BLS) No visit or technical changes

Blussuvoll

(TBLU)

No visit or technical changes

Dombås

(DOMB)

25.07.16: Station down since 23.07 at 00:08 (UTC). Unknown reason. Power

on/off restarted the station.

02.08.16: Station down since 30.07 at 22:30 (UTC). Unknown reason. Power

on/off restarted the station.

Fauske

(FAUS)

26.03.16: Vault checked by local contact.

07.04.16: El. enclosure was inspected by local contact. No humidity or other

problems were detected.

18.05.16: Station was visited by UiB staff. Small amount of water was

removed from the vault.

11.11.16: The station vault was inspected by the local contact.

Florø (FOO) No visit or technical changes.

Hammerfest

(HAMF)

No visit or technical changes.

Homborsund

(HOMB)

11.11.16: Station down since 06.11.16 due to power-loss. All data lost.

Hopen 18.03.16: UPS installed by local personnel.


6

(HOPEN) 04.04.16: The vault was inspected by local personnel. No problems found.

Høyanger

(HYA)

15.02.16: Station down since 29.01.16 due to PC problems after heavy

storm. PC replaced by local contact. Data lost.

20.05.16: Station down since 16.05.16 due to power failure. Data lost.

Jan Mayen

Trolldalen

(JMI)

No technical changes. The station is visited by local personnel.

The cable to the equipment developed a fault during November.

Jan Mayen

Ulla (JNE)

August 2016: The digitizer for JNE and JNW started showing signs of

malfunction.

November 2016: The station is visited by local personnel who found that the

windmill did not produce any power due to a broken cable. The

problem was fixed locally.

(Photo: Local staff at Jan Mayen)

Jan Mayen

(Liberg)

JNW

September 2016: No technical changes. The station is visited by local

personnel.

(Photo: Local staff at Jan Mayen)

Karmøy

(KMY)

23.09.16: Visit. New broad band sensor (Trillium 120QA) installed.

02.11.16: USB memory connected 01.11.16 by local contact. Formatted

remotely and put into use 02.11.16

Kautokeino

(KTK)

19.08.16: Seismometer not working since 29.07.16. Local contact visited and

repowered the station, which resolved the problem. Data lost.

Kings Bay No visit or technical changes.

http://jan.mayen.no/wp-content/uploads/2016/11/Seismo1.jpg

http://jan.mayen.no/wp-content/uploads/2016/11/Seismo3.jpg


7

(KBS)

Kongsberg

(KONO)

The USGS plans to move the station to a different site within the mine.

Currently they are still in the process of arranging for the work that

needs to be done.

Konsvik

(KONS)

15.08.16: Station visited, no changes.

Lofoten

(LOF)


Mo i Rana

(MOR8)

08.03.16: New UPS installed by local operator.

Molde

(MOL)


Namsos

(NSS)


Odda

(ODD1)

22.09.16: New broad band seismometer (Trillium 120QA) installed. The

digitizer (Guralp) was not changed.

03.11.16: Visit by local contact. USB memory connected to digitizer. Trees

near the sensor were cut to prevent noise.

Oslo (OSL) No visit or technical changes.

Skarslia

(SKAR)

30.06.16: Vault inspection. A small amount of water was removed.

04.07.16: Station down since 29.06 due to problem with the digitizer. Data

lost.

25.07.16: Station down since 25.07 at 04:30 UTC. A digitizer problem.

Power off/on and station ok from 08:32.

07.09.16: Station down from 19.08.16. Problem with digitizer. The digitizer

was replaced by local contact. A small amount of water was removed.

Snartemo

(SNART)


Stavanger

(STAV)


Steigen

(STEI)

19.05.16: Station was shortly visited by UiB staff who had fieldwork in the

area.

Stokkvågen

(STOK)

15.08.16: Station visited, no changes.

22.09.16: Station down some hours due to power failure. Data lost.

Sulen (SUE) 16.02.16: Visit. A new Guralp digitizer was installed, and old digitizer and PC

were removed. There had been timing problems for some time and a


8

new GPS antenna was installed.

Tromsø

(TRO)

26.07.16: Station down since 24.07. Power reset remotely. Data lost.

Vadsø

(VADS)

29.09.16: The station was installed with the following equipment: Trillium

120PA sensor and a Guralp CMG-DM24 digitizer.

2.3 The NORSAR stations and arrays

NORSAR is operating the following installations:

NOA (southern Norway, array, 42 sites, 7 3C broadband sensors and 35 vertical

broadband sensors)

ARCES (Finmark, array, 25 sites, 25 3C broadband seismic sensors, 9 infrasound

sensors)

SPITS (Spitsbergen, array, 9 sites, 6 3C broadband sensors and 3 vertical broadband

sensors)

NORES (Hedmark, array, 12 3C short-period sensors, 9 infrasound sensors)

JMIC (Jan Mayen, 3C broadband sensor)

AKN (Åknes, Møre og Romsdal, 3C broadband sensor)

TROLL (Antarctica, 3C broadband sensor)

IS37 (Bardufoss, infrasound array, 10 sites)

JETT (Jettan, Troms, 3C broadband sensor)

I37H0 (Bardufoss, 3C broadband sensor)

In addition NORSAR receives and processes data in near realtime from:

FINES (southern Finland, array, 16 sites, 2 3C broadband sensor, 1 3C short-period

sensor and 15 short-period vertical sensors, operated by Institute of Seismology,

Helsinki, Finland)

HFS (Hagfors, Sweden, 10 sites, 1 3C broadband sensor and 9 short-period vertical

sensors, operated by the Swedish Defence Reseearch Agency, Stockholm, Sweden)

EKA (Eskdalemuir, United Kingdom, 20 sites, 1 3C broadband sensor and 20 short-

period vertical sensors, operated by the United Kingdom National Data Centre, AWE

Blacknest, UK)

BRBA, BRBB (Barentsburg, 2 3C broadband sensors and 3 infrasound sensors)

APA (Apatity seismic array, parametric data)

All NORSAR waveform data and parametric data are openly available and can be accessed

through web-interfaces or direct means. The NORSAR webpage www.norsardata.no provides

access to general station information, to automatic and reviewed seismic bulletins, to real-

time plots of short and long-period data, and to an AutoDRM request form for waveform data

retrieval.

The seismic array data are automatically processed and analysed. The fastest near realtime

process ‘Automatic Alert’ is based on single array detection and provides event locations

within a few (1-3) minutes delay. The alerts with event and location details are published

immediately on http://www.norsardata.no/NDC/ael/eventmap1.html (which is also integrated

http://www.norsardata.no/

http://www.norsardata.no/NDC/ael/eventmap1.html


9

into the NNSN website). A second automatic process called GBF (Generalized Beam

Forming) awaits for automatic phase picks from all arrays and delivers more reliable/accurate

results within up to a few hours delay. Automatically processed seismic events with

magnitude larger than 2 (or 1.5 if the event is of special interest) are manually analysed and

reviewed. In this step all available waveforms (also from single stations) are utilized.

Graphical displays and parametric event data and for ‘Automatic Alert’, ‘GBF’ and

‘Reviewed bulletins’ can be found on http://www.norsardata.no/NDC/bulletins/.

Figure 3. NORSAR seismic arrays/stations (NOA, NORES, ARCES, SPITS, JMIC, AKN, I37H0) and

contributing arrays/stations (HFS, FINES, EKA, BRBA, APA).

Changes during 2016

a) In 2016 we completed the renovations of the ARCES array. Sensors, digitizers and central

acquisition system had been upgraded in 2014. The main tasks in 2016 was the

refurbishment of the Central Recording Facility (CRF), the installation of an

uninterruptable power supply (UPS), finalizing of the central acquisition rack and the

http://www.norsardata.no/NDC/bulletins/


10

official revalidation of the ARCES/PS28 primary station of the international monitoring

sytem (IMS). Figure 4 shows the renovated CRF with satellite, cell-network

communication antenna, GPS-antenna for central timing on the gable and the mains power

transformer in the background.

Figure 4. The renovated Central Recording Facility (CRF) of the ARCES array

b) We installed three more sites of the NORES array. It consists now of 12 3-component

seismometers and 9 infrasound sensors The A-and B-ring are equipped with 9

seismometers and 9 infrasound sensors. Three out of the 7 sites of the C-ring got

seismometers and the remaining 4 sites will be installed during 2017. The research facility

‘Stendammen’ in the centre of the NORES array has been equipped with a small

workshop and it provides accommodation for 2 persons.

c) NORSAR’s IMS infrasound station in Bardufoss IS37 has been upgraded with a second

infrasound sensor at each site in order to facilitate remote calibration of the entire system

(i.e. sensors and wind noise reduction system). As a consequence, we could not use

anymore a common digitizer for infrasound sensor and seismometer, and had to install a

separate digitizer for the seismic sensor at site H0 (see picture below).

Figure 5. The instruments at the Bardufoss site.


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Data availability

All data recorded at NORSAR are continuous. The following table provides a monthly

overview on the data availability of 13 main data streams provided by NORSAR to NNSN.

Table 3. Systems recording performance (in % of data completeness) for 14 main data streams provided

from NORSAR to NNSN.

ARA0 JMIC NAO01 NBO00 NB201 NC204 NC303

Jan 99.99 100.00 99.81 99.97 99.99 99.94 99.98

Feb 99.98 99.99 99.83 99.96 99.99 99.97 99.99

Mar 100.00 100.00 99.99 99.99 99.99 99.98 99.99

Apr 100.00 100.00 99.98 99.99 100.00 100.00 100.00

May 99.98 100.00 100.00 100.00 99.99 99.99 100.00

Jun 99.99 100.00 99.99 99.99 99.99 99.99 99.99

Jul 99.99 100.00 99.99 99.99 99.99 99.99 99.99

Aug 99.99 100.00 99.99 99.99 99.99 99.99 97.98

Sep 99.70 100.00 99.97 99.96 99.97 99.97 97.79

Oct 99.97 100.00 99.99 99.98 99.98 99.99 99.99

Nov 100.00 100.00 100.00 99.95 100.00 99.97 99.99

Dec 99.99 99.98 99.99 99.99 99.99 99.98 99.99

NC405 NC602 SPA0 AKN JETT HFC2 I37H0

Jan 99.99 98.37 99.99 100.00 99.99 99.96 100.00

Feb 99.98 99.99 100.00 100.00 100.00 99.98 100.00

Mar 99.99 100.00 94.66 100.00 100.00 99.96 100.00

Apr 99.98 100.00 99.99 100.00 99.99 99.97 100.00

May 99.99 99.99 99.99 100.00 100.00 99.96 100.00

Jun 99.97 99.97 100.00 100.00 99.98 94.23 99.98

Jul 99.98 100.00 100.00 100.00 100.00 99.96 99.41

Aug 99.97 99.98 99.99 100.00 100.00 99.95 99.99

Sep 99.92 99.97 99.99 100.00 99.99 99.98 99.99

Oct 99.92 99.99 99.98 100.00 100.00 99.92 100.00

Nov 99.97 99.99 96.83 100.00 100.00 99.91 100.00

Dec 99.98 99.99 100.00 100.00 100.00 99.93 100.00

Detections

The NORSAR analysis results are based on automatic phase detection and automatic phase

associations which produce the automatic bulletin. Based on the automatic bulletin a manual

analysis of the data is done, resulting in the reviewed bulletin. The automatic bulletin for

northern Europe is created using the Generalized Beam Forming (GBF) method. This

bulletin (www.norsardata.no/NDC/bulletins/gbf/) is subsequently screened for local and

regional events of interest in Fennoscadia and in Norway, which in turn are reviewed by an

analyst. Regional reviewed bulletins from NORSAR are available from 1989 and from 1998

onwards they are directly accessible from via internet

http://www.norsardata.no/NDC/bulletins/gbf/


12

(www.norsardata.no/NDC/bulletins/regional/). Table 4 gives a summary of the phase

detections and events declared by GBF and the analyst.

Table 4. Phase detections and event summary.

Jan. Feb. March April May June

Phase detections 286341 219734 201448 220043 204357 240687 Associated phases 12810 10632 10721 10442 10319 14181 Un-associated phases 273531 209102 190727 209601 194038 226506 Screened GBF events for

Fennoscandia/Norway 2611 1950 1985 2020 2004 2909

No. of events defined by the

analyst 62 50 55 36 44 45

July Aug. Sep. October Nov. Dec.

Phase detections 257040 340170 351153 353327 325144 281070

Associated phases 18589 31937 33895 5365 5207 5346

Un-associated phases 238451 308233 317258 347962 319937 275724

Screened GBF events for

Fennoscandia/Norway 3931 6873 7412 511 458 484

No. of events defined by

the analyst 46 42 29 22 33 27

http://www.norsardata.no/NDC/bulletins/regional/


13

3 NNSN achievements and plans

The overall purpose of the NNSN is to provide data both for scientific studies, but equally

important for the routine observation of earthquakes. This in principle means that broadband

seismometers are desired at all sites. However, in areas where additional stations are deployed

for local monitoring, short-period seismometers are sufficient. The number of broadband

seismometers in the network will be increased to replace existing short period instruments. A

general goal for the future development has to be to achieve better standardization in

particular with the seismometers and digitizers. The total number of stations for now should

remain stable, but it is important to improve the overall network performance.

3.1 NNSN achievements in 2016

The new broadband station near Vadsø (VADS) on the Varanger peninsula has been

completed and the first event was recorded October 27th

at 03:53 (UTC).

The two short-period stations ODD1 and KMY have been upgraded with broadband

seismometers.

The archiving procedure at UiB has been modified, which together with improved

station robustness has resulted in increased data completeness.

The UiB research has focussed on Lg wave attenuation tomography.

The UiB magnitude study for the North Atlantic is being finalized and a paper will be

submitted in 2017.

NORSAR have continued their studies on event re-location and source discrimination.

Under the EPOS project, planning and preparation for the 6 Svalbard, 7 Nordland and

3 Jan Mayen stations has started, the seismic instruments have been purchased.

Stations deployed under the NEONOR2 project have been uninstalled, detailed

processing of the earthquake swarm near Jektvik that started in April 2015 has been

carried out. The data are integrated with the NNSN stations and are part of the NNSN

database.

3.2 NNSN plans for 2017

Upgrade three more stations with broadband seismometers.

The Kongsberg station may be upgraded by the USGS.

Implement the new magnitude scale into the processing routines.

UiB plans to carry out research on source parameters, automatic detection and

determination of fault plane solutions.

A research workshop will be held between UiB and NORSAR early in 2017 (done).

The research and development activity will continue in close collaboration between

UiB and NORSAR.

Provide data through IRIS and through a European EIDA node at UiB under the

EPOS-Norway project.


14

Strengthen the collaboration with NORSAR and the other Nordic countries on data

processing through technical visits.

Integrate more real-time continuous data from stations located in Sweden and Iceland

if available.

Improve macroseismic questionnaire in collaboration with other Scandinavian

countries.

Make the macroseismic data available on the website through the EPOS-Norway

project.

Jan Mayen data will be send to UiB in real-time.

Continue collaboration with other Nordic countries to collect information about

historical felt earthquakes.

3.3 Projects related to NNSN

3.3.1 Status update for EPOS-IP and EPOS-N

European Plate Observing System – Implementation Phase (EPOS-IP) (www.epos-

ip.org)

EPOS is currently well underway in the Implementation Phase (EPOS-IP: 2014-2019),

heading towards the Operational Phase (EPOS-OP) from 2020 onwards. The ongoing

Implementation Phase aims to implement key structural pillars of the project. During 2016, it

was decided that the EPOS-ERIC legal seat will be at the INGV headquarters in Rome, Italy,

and will be operational in 2018. Considerable progress has been made in the IT architecture

and development of the interoperable services. ICS developments (software for the EPOS

portal) include an integration of the web components and metadata harvesting. The thematic

core services have undergone a community development by adopting their metadata to the

baseline model and providing services for their data. In June 13-15, 2017 a dedicated Nordic

EPOS Conference is planned in Helsinki hosted by the University of Helsinki. The purpose of

this conference is to bring together various EPOS contributors from the Nordic countries and

find possible collaboration points and provide synergies.

European Plate Observing System – Norway (EPOS-N) (www.epos-no.org)

The EPOS-Norway (EPOS-N) project shares the goals and visions of the EPOS project about

addressing key challenges in Earth science, but with special attention to the Arctic. In January

2017, EPOS-N arranged its 2nd

annual workshop in Bergen as a conclusion of the first year for

the EPOS-N project. Considerable progress has been made on a number of fields. The

Enlighten software has been chosen as the engine behind the Norwegian EPOS web-portal.

Implementation of macroseismic data is ongoing through the MIDOP service. EPOS-N has

applied for EIDA membership to provide the NNSN and EPOS data. The Solid Earth Science

Forum (SESF) is in the establishment phase, and a committee (SESC) consisting of

representatives from six partner institutions has been established to coordinate this forum. An

External Advisory Board (EAB) has been established, with five members from both Norway

and other European countries. EAB also had its first meeting during this year’s EPOS-N

Annual Workshop, where they provided comments to the project progress and the Annual

Report, and selected a chair. The first Annual Report was submitted in January 2017.

http://www.epos-ip.org/

http://www.epos-ip.org/

http://www.epos-no.org/


15

Upcoming challenges include construction of the monitoring stations in the Arctic. A

reconnaissance survey around Svalbard is planned this summer, where potential sites for new

stations will be inspected. Procurement of seismological equipment is already completed and

the instruments are shipped to locations in Norway, Svalbard and Jan Mayen.

3.3.2 Historical earthquake database for Norway

Norwegian earthquakes have been documented at least back to the mid-17th century. A rich

dataset on historical earthquakes is available in terms of eye-witness reports, newspaper

articles, macroseismic questionnaires and published and unpublished macroseismic intensity

maps. However, this data has not been compiled and assessed systematically in terms of

macroseismic intensities. In 2016, an effort was initiated to compile all available intensity

data for Norway and make it available through an online system. Currently, all data which

were available in the NNSN database have been included in the new system, and a prototype

is available online (http://nnsn.geo.uib.no/midop/).

The online database is developed using the MIDOP tool which has been developed in relation

to the European Archive of Historical Earthquake Data (AHEAD) to encourage the adoption

of common compilation standards and compatible data formats among macroseismic intensity

data compilers. All available data for events before 1900 will be integrated in the European

AHEAD database when ready. The database allows searching for information by earthquake

(showing all intensities observed for a given earthquake) or by locality (showing all intensities

observed in different earthquakes at a given locality). Selected features of the data access

system are shown in Figure 6 and Figure 7.

Figure 6. Entry page when accessing information by earthquake. The upper left table presents a list of

events for which intensity data is available. The event locations are shown in the map.


16

Figure 7. Intensity data for a specific earthquake. The lower left table presents the intensity data for each

locality, which is also shown in the map.

Currently, the focus is on including all available data from other sources. We are

systematically working through all maps and tables with intensity data available in the

published literature and the UiB archive, and digitizing the information. This will add a

significant amount of new data to the database which will, when finalized, contain

information at least back to 1657. In addition to making the valuable historical earthquake

dataset available to the wider community, this effort will help improving the completeness of

the NNSN database for historical events.

4 Seismicity of Norway and surrounding areas for 2016

The earthquake locations presented have been compiled from all available seismic stations as

described above. All phase data are collected by UiB and all located local and regional

earthquakes recorded on NNSN stations are presented on the web pages. The largest are also

e-mailed to the European-Mediterranean Seismological Centre (EMSC) to be published on

the EMSC web pages. When all available data is collected, a monthly bulletin is prepared

and distributed. A brief overview of the events published in the monthly bulletins is given in

this annual report. Macroseismic data for the largest felt earthquakes in Norway are

collected, and macroseismic maps are presented.

Local, regional and teleseismic events that are detected by the UiB network are included.

The merging of data between NORSAR and UiB is based on the following principles:

i) All local and regional events recorded by NORSAR that are also detected by the

NNSN network are included.

ii) Local and regional events with local magnitude larger than 1.5 detected by

NORSAR and not recorded by the NNSN are included. However, probable

explosions from the Kiruna/Malmberget area are not included.


17

iii) All teleseismic events recorded by NORSAR and also detected by the NNSN are

included.

iv) All teleseismic events with NORSAR magnitude Mb5.0 are included even not

detected by the NNSN.

Data from the British Geological Survey (BGS) and the Geological Survey of Denmark and

Greenland (GEUS) are included in the database in Bergen following similar criteria as

mentioned above, however only events located in the prime area of interest, 54-85°N and

15°W-35°E, and with magnitude ≥ 2.0 are included. From the Greenland area only

earthquakes recorded on NNSN stations are included. Phase data and locations from

University of Helsinki and University of Uppsala are included NNSN database to improve

NNSN locations for events in the eastern parts of Norway or possibly for larger events

elsewhere.

Many of the recorded events are explosions. To discriminate between natural earthquakes

and manmade explosions, spectrograms are used in the daily routine processing. This was

implemented in the processing in Bergen during spring 2015.

4.1 Velocity models and magnitude relations

The velocity model used for locating all local and regional events, except for the local Jan

Mayen events, is shown in Table 5 (Havskov and Bungum, 1987). Event locations are

performed using the HYPOCENTER program (Lienert and Havskov, 1995) and all

processing is performed using the SEISAN data analysis software (Havskov and Ottemöller,

1999).

Table 5. Velocity model used for locating all local and regional events, except for the local Jan Mayen

events (Havskov and Bungum, 1987).

P-wave velocity

(km/sec)

Depth to layer

interface (km)

6.2 0.0

6.6 12.0

7.1 23.0

8.05 31.0

8.25 50.0

8.5 80.0

Local magnitude ML is computed for all earthquakes based on measuring instrument

corrected ground amplitudes A (nm) and applying the ML scale by Alsaker et al. (1991):


18

ML= log (A) + 0.91 log(D) + 0.00087 D - 1.67

where D is the hypocentral distance in km.

The moment magnitude Mw is calculated for selected earthquakes on mainland Norway from

the seismic moment M0 using the relation (Kanamori, 1977)

Mw = 0.67 log(M0) – 6.06

The unit of M0 is Nm. The seismic moment is calculated from standard spectral analysis

assuming the Brune model (Brune, 1970) and using the following parameters:

Density: 3.0 g/cm2

Q = 440 f 0.7

P-velocity = 6.2 km/s

S velocity = 3.6 km/s

In the analysis, the seismic moment is measured from attenuation corrected source

displacement spectra (Havskov and Ottemöller, 2003).

For the Jan Mayen area, a local velocity model (see Table 6) and coda magnitude scale is

used (Andersen, 1987).

Table 6. Velocity model used for locating local Jan Mayen events.

P-wave velocity

(km/sec)

Depth to layer

interface (km)

6.33 18

8.25 50

The regional and teleseismic events recorded by the network are located using the global

velocity model IASPEI91 (Kennett and Engdahl, 1991).

Body wave magnitude is calculated using the equation by Veith and Clawson (1972):

Mb = log(A/T) + Q(D,h)

Here h is the hypocentre depth (km), A is the amplitude (microns), T is period in seconds

and Q(D,h) is a correction for distance and depth.

Surface wave magnitude Ms is calculated using the equation (Karnik et al., 1962):

Ms = log(A/T) + 1.66 log(D) + 3.3

where A is the amplitude (microns), T is period in seconds and D is the hypocentral distance

in degrees.

Starting from January 2001, the European Macroseismic Scale, EMS98, (Grünthal, 1998) has

been used. All macroseismic intensities mentioned in the text will refer to the EMS98 instead


19

of the previously used Modified Mercalli Intensity scale. The two scales are very similar at

the lower end of the scale for intensities less than VII.

4.2 Events recorded by the NNSN

Based on the criteria mentioned above, a total of 8,182 local and regional events, were

detected by the NNSN during 2016. Of these local and regional events, 34% were large

enough to be recorded by several stations and hence could be located reliably, and are not

classified as explosions (LP or LE). The numbers of local/regional and teleseismic events,

recorded per month in 2016 are shown in Figure 8.

0

100

200

300

400

500

600

700

800

900

JAN MAR MAY JUL SEP NOV

Figure 8. The number of recorded local/regional (blue) and teleseismic (red) events during 2016. The

average number of local and regional events recorded per month is 682 (570 in 2015).

A total of 1159 teleseismic events were recorded in 2016 and the monthly average of

teleseismic earthquakes in the NNSN database, is 96. In addition to the locations determined

at UiB and NORSAR, also preliminary locations published by the USGS (United States

Geological Survey) or the EMSC (European Mediterranean Seismological Centre) based on

the worldwide network are included for earthquakes registered by NNSN stations.

During the years there has been an increase in the number of local/regional events recorded

into the NNSN database. As can be seen from Figure 9 the number of teleseismic (D)

earthquakes recorded are relative stable while the number of local/regional (L/R) events have

increased the last four years. The temporary stations in the NEONOR project can explain

some of the increase. The number of recorded earthquakes is expected to continue to increase

with the planned installation of new stations on Svalbard.


20

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

L/R

D

Figure 9. Number of local/regional (blue) and teleseismic (pink) events recorded in the NNSN database

since 2000

UiB, as an observatory in the global network of seismological observatories, reports local

and teleseismic phases to the International Seismological Center (ISC). All events

(teleseismic, regional and local) recorded from January to December 2016 with M 3 are

plotted in Figure 10.

Figure 10. Epicentre distribution of earthquakes with M3.0, located by the NNSN from January to

December 2016. Teleseismic events recorded only by NORSAR have M5.0.

Monthly station recording statistics from January to December 2016 are given in Table 6 and

7. This table shows, for each station, local events recorded on more than one station and

recorded teleseismic events. The statistics are based on the analysed data and are taken from

the database. Table 6 and 7 show both earthquakes and explosions. Identified or suspected

explosions will only be located with a minimum number of stations. Therefor some stations

(e.g. KTK, MOR8, VADS, FAUS) will have a higher number of detections.

The following was observed from Table 6 and 7:

At Jan Mayen there was a problem with the digitizer which reduced the number of

earthquakes triggered since summer 2016.

TBLU and OSL are recording mostly teleseismic earthquakes, which is as expected

due to their location in noisy environment. Stronger local earthquakes will, however,

be detected.


21

The new station in Vadsø (VADS) was operational since October 2016.

The stations KONS, STOK and MOR8 continue to record a relatively large number of

small earthquakes and explosions in the area.

There are no teleseismic detections on JMI, JNE and JNW as currently the system on

Jan Mayen is only detecting local events, and realtime data is not available at UiB.

Table 7. Monthly statistics of events recorded at each station for January-June 2016. Abbreviations are:

L = Number of local events recorded at more than one station and D = Number of teleseismic events

recorded at the station.

JANUARY FEBRUARY MARCH APRIL MAY JUNE STATION L D L D L D L D L D L D ASK 26 31 35 19 43 17 47 44 34 40 53 36 BER 8 25 16 20 12 19 21 40 20 51 18 34 BJO1 40 18 8 11 37 9 31 36 35 30 27 32 BLS5 29 29 41 18 41 21 41 56 33 50 37 43 DOMB 12 42 27 28 23 37 23 64 20 63 17 53 FAUS 77 41 86 39 61 41 67 75 44 66 70 65 FOO 17 26 18 10 29 13 27 35 25 36 36 33 HAMF 22 37 15 36 22 22 18 65 16 61 18 56 HOMB 20 28 20 19 25 20 22 42 8 34 16 29 HOPEN 88 12 46 9 99 9 111 34 71 22 91 21 HYA 29 26 19 8 48 21 45 45 35 29 54 32 JMI 17 0 11 0 5 0 16 0 25 0 54 0 JMIC 22 6 13 1 6 4 17 13 31 8 56 11 JNE 20 0 12 0 6 0 17 0 24 0 40 0 JNW 21 0 11 0 6 0 17 0 27 0 46 0 KBS 136 26 100 17 178 12 143 36 128 33 129 43 KMY 15 16 22 11 33 14 29 0 29 35 36 33 KONO 51 28 57 19 37 31 43 50 49 54 35 52 KONS 71 33 81 30 68 26 57 58 48 51 49 39 KTK1 67 47 63 43 49 44 67 77 39 75 76 65 LOF 24 25 31 26 19 20 12 51 12 46 25 44 MOL 5 24 10 20 10 21 8 30 14 37 15 37 MOR8 69 42 72 29 61 39 57 72 39 59 51 59 NSS 12 40 23 37 12 34 5 66 6 62 11 49 ODD1 31 36 41 20 43 25 29 40 17 33 16 32 OSL 26 28 28 19 14 27 20 34 20 36 6 27 SKAR 79 40 83 29 62 35 70 64 74 60 84 56 SNART 18 26 26 15 28 23 28 35 28 37 29 36 STAV 6 22 12 17 6 13 8 29 11 29 11 30 STEI 62 42 70 40 39 39 20 73 26 72 68 61 STOK 54 15 49 11 48 9 18 31 27 31 30 9 SUE 26 18 26 14 45 17 36 36 35 37 52 28 TBLU 3 19 5 14 1 18 1 30 0 31 2 31 TRO 14 36 12 38 10 36 7 67 7 71 14 59 VADS - - - - - - - - - - - - AKN 22 37 29 28 39 25 40 54 32 44 44 43 JETT 41 37 27 34 25 41 25 71 14 66 39 50 NORSAR 15 67 12 53 14 67 14 97 9 84 14 92 ARCES 104 48 93 40 74 39 83 75 90 72 102 57 SPITS 151 41 111 32 187 21 151

1 71 137 72 134 49


22

Table 8. Monthly statistics of events recorded at each station for July-December 2016. Abbreviations are:

L = Number of local events recorded at more than one station and D = Number of teleseismic events

recorded at the station.

JULY AUGUST SEPT OCT NOV DEC

STATION L D L D L D L D L D L D ASK 40 36 56 30 39 26 65 28 46 17 47 12 BER 9 31 19 31 13 20 25 32 16 13 12 10 BJO1 17 25 36 29 16 14 14 19 10 7 3 9 BLS5 28 38 49 36 45 39 70 39 60 25 50 16 DOMB 12 48 16 52 27 66 44 56 32 48 23 32 FAUS 87 55 130 80 159 83 158 66 160 71 68 34 FOO 30 32 36 28 28 25 42 20 27 14 26 7 HAMF 32 39 49 56 34 57 54 48 53 42 29 23 HOMB 10 28 27 24 43 29 36 23 32 18 30 14 HOPEN 79 16 70 15 56 16 46 10 32 6 25 7 HYA 47 38 53 29 42 33 68 30 50 15 45 11 JMI 25 0 39 0 9 0 3 0 7 0 3 0 JMIC 31 15 45 10 12 8 6 7 11 5 3 4 JNE 29 0 33 0 9 0 2 0 1 0 3 0 JNW 29 0 31 0 7 0 1 0 1 0 0 0 KBS 146 29 135 35 155 27 152 24 112 16 88 9 KMY 27 30 46 23 36 12 60 19 43 6 36 1

KONO 32 45 31 47 40 55 38 49 54 36 27 21 KONS 19 36 58 36 68 51 71 30 68 23 53 17 KTK1 117 45 99 31 237 95 221 78 226 85 145 48 LOF 20 31 52 37 46 40 49 32 53 18 24 12 MOL 10 36 13 32 12 34 16 26 10 16 10 10 MOR8 24 42 65 61 95 77 115 64 98 45 52 29 NSS 11 49 16 54 18 70 26 57 14 43 18 27 ODD1 20 34 40 34 33 32 59 33 59 25 54 15 OSL 0 26 4 32 9 28 9 36 16 12 13 10 SKAR 50 44 50 24 101 46 117 51 118 41 83 27 SNART 15 39 32 27 41 30 51 32 39 16 33 15 STAV 6 31 11 22 15 23 23 21 18 8 17 7 STEI 60 50 115 76 141 88 139 66 136 68 56 33 STOK 4 13 21 4 57 12 65 19 58 15 45 12 SUE 42 30 48 26 42 19 66 22 42 13 39 7 TBLU 1 31 2 28 3 32 2 26 1 12 3 9 TRO 26 42 52 67 53 78 47 66 52 61 30 31 VADS - - - - - - 7 0 60 22 93 35 AKN 42 38 44 40 46 54 68 40 46 30 36 13 JETT 54 36 136 71 94 69 94 63 106 52 69 35 NORSAR 9 81 12 95 11 112 7 92 5 91 7 62 ARCES 182 28 213 75 171 91 215 81 196 76 137 47

SPITS 158 12 145 45 160 51 163 38 114 32 88 29

4.3 The seismicity of Norway and adjacent areas

This section first gives an overview of the seismicity in the monitoring area before presenting

the activity in specific areas in more detail.

The main area of interest is defined as 54-82N and 15W-35E, Figure 11. We also show the

seismicity for the Arctic region including the Barents Sea defined by coordinates 65-85°N and

25°W-50°E. A total of 5074 of the recorded events are located inside the NNSN prime area.

During analysis and using the explosion filter (Ottemöller, 1995), 54% of these events were

identified as confirmed or probable explosions, or induced events. Figure 11 shows all

local/regional events in the prime area, analysed and located during 2016. Among these, 199

are located in the vicinity of the Jan Mayen Island.


23

Figure 11. Epicentre distribution of events analysed and located in 2016. Earthquakes are plotted in red.

Probable and confirmed explosions and induced events are plotted in blue. For station locations, see

Figure 1.

It should be emphasized that the magnitude calculation for the earthquakes located on the

oceanic ridge in the Norwegian Sea uses the same formula as for mainland Norway. As the

scale is not appropriate for this region, the magnitudes for these earthquakes are

underestimated. A new magnitude scale has been developed, but is not yet applied routinely.

Most of the recorded earthquakes in this area have magnitudes above 3.0 if they are recorded

on Norwegian mainland stations.

Figure 12 shows the location of earthquakes (induced events, known and probable explosions

removed) located within the prime area with one of the calculated magnitudes above 3. Table

9 lists the same earthquakes with all earthquakes located close to the Mid-Atlantic ridge

removed.


24

Figure 12. Epicentre distribution of located events with one of the calculated magnitudes above or equal to

3.0. For station location, see Figure 1.

The largest local or regional earthquake in 2016, recorded on Norwegian stations and within

the prime area, was a double event that occurred on March 29th

at 10:32:10 (UTC) and

10:32:38 (UTC) in Storfjorden, west of Edgeøya. The earthquakes has magnitudes of

ML(BER)=5.2 and ML(BER)=4.8, respectively. Seismograms for the two earthquakes recorded at

Barentsburg (BRBA), Hornsund (HSPB), Hopen (HOPEN) and Kings Bay (KBS), are shown

in Figure 13. The P-wave onset for the first earthquake and the S-wave onset from both

earthquakes are clearly seen. These earthquakes were followed by several aftershocks, where

six had an estimated magnitude above 3.0.


25

Table 9. Earthquakes located in the vicinity of mainland Norway and in the Svalbard area (grey

background) with any reported magnitude above or equal to 3.0 for the time period January through

December 2016. In cases where all BER magnitudes are below 3 but the event still is included in the list,

NORSAR (NAO), GEUS- Geological Survey of Denmark and Greenland (DNK), University of Uppsala

(UPP), University of Helsinki (HEL) or the British Geological Survey (BGS) has reported a magnitude of

3.0 or larger. Abbreviations are: HR = hour (UTC), MM = minutes, Sec = seconds, L = distance

identification (L=local, R=regional, D=teleseismic), Latitud = latitude, Longitud = longitude, Depth = focal

depth (km), F = fixed depth, AGA = agency (BER=Bergen), NST = number of stations, RMS = root mean

square of the travel-time residuals, Ml = local magnitude and Mw = moment magnitude.

Year Date HRMM Sec L Latitud Longitud Depth F AGA NST RMS Ml Mw ML ML

NAO

2016 110 0122 40.8 L 76.865 18.461 15.0 BER 13 0.7 2.5 3.0

2016 111 1642 41.1 L 76.861 18.309 20.5 BER 12 0.5 2.7 3.2

2016 111 2102 31.4 L 76.916 18.362 18.3 BER 24 0.5 3.5 4.0 4.3

2016 112 0048 31.8 L 76.927 18.371 15.0 BER 20 0.7 3.3 3.7 3.7

2016 3 3 0316 12.5 L 76.905 18.652 15.0 BER 9 0.6 2.6 2.9 3.0

2016 3 3 1030 14.7 L 76.906 18.347 15.0 BER 15 0.7 2.9 3.3 3.5

2016 3 7 0540 34.8 L 61.703 3.692 12.6 BER 28 0.5 2.7 2.9 3.0

2016 312 1804 6.8 L 76.842 18.371 18.1 BER 10 0.7 2.5 3.0

2016 319 2155 32.6 L 65.027 22.552 15.7 BER 88 0.9 4.2 4.2 4.7 4.2UPP

2016 329 1032 10.4 L 77.830 21.051 15.0 BER 41 1.0 5.2

2016 329 1032 38.7 L 77.890 20.674 2.3 BER 5 0.6 4.8

2016 329 1040 48.8 L 77.744 20.578 15.0 F BER 8 0.9 3.2 3.3 3.3

2016 329 1509 2.3 L 77.810 20.741 15.0 BER 15 0.7 3.1 3.3 3.1

2016 329 1813 46.1 L 77.921 21.305 23.0 BER 16 0.6 3.4 3.7 3.4

2016 330 0355 50.8 L 77.748 20.651 15.0 BER 15 0.8 3.3 3.5 3.4

2016 330 0438 10.1 L 77.760 20.536 22.8 BER 14 0.6 3.2 3.5 3.3

2016 4 2 1935 44.7 L 76.875 18.542 18.3 BER 8 0.5 2.6 3.1 2.7

2016 417 0845 4.1 L 64.910 5.124 17.6 BER 29 0.6 2.3 3.1 2.3HEL

2016 5 4 1154 20.9 L 76.854 18.340 15.0 BER 10 0.6 2.7 3.3 3.4

2016 520 1920 24.7 L 74.292 14.179 24.8 BER 22 0.6 2.4 3.0 3.7

2016 526 1955 47.0 L 64.422 -4.286 15.0 BER 29 0.9 2.6 3.3 3.3BGS

2016 613 0435 10.2 L 64.395 -4.400 15.0 BER 35 0.7 2.5 2.8 3.6

2016 621 1922 28.6 L 77.281 18.227 4.0 BER 10 1.6 2.9 3.5 3.4

2016 627 1115 0.4 L 77.179 24.002 15.0 BER 20 0.9 3.4 3.7 4.1

2016 7 2 0826 30.4 L 82.969 33.920 15.0 F BER 9 0.7 2.4 3.1

2016 7 9 0439 39.2 L 76.971 18.748 15.0 F BER 9 0.5 2.7 3.2

2016 719 1640 3.0 L 76.941 15.724 1.5 BER 10 0.5 2.8 3.3 3.4

2016 728 0531 26.1 L 76.890 18.610 5.5 BER 13 0.6 3.0 3.3 3.6

2016 730 1023 29.6 L 70.926 -6.659 10.0 F BER 42 1.4 3.4 4.5

2016 8 5 0355 26.1 L 66.680 -1.746 10.0 F BER 39 1.2 2.4 3.1

2016 812 2047 53.0 L 83.749 0.354 10.0 F BER 22 1.8 3.0 4.8

2016 826 1208 2.0 L 76.214 23.321 15.0 F BER 11 0.8 2.6 3.2 3.0

2016 829 1842 38.8 L 76.903 18.117 14.0 BER 9 0.7 2.8 3.0

2016 9 3 0132 53.3 L 76.980 18.127 15.0 F BER 10 0.8 3.1 3.6 3.4

2016 9 3 0655 39.2 L 71.078 -7.980 10.0 F BER 60 2.3 4.2 5.1EMSC

2016 9 7 0902 53.5 L 70.987 -6.681 0.0 BER 4 0.1 3.0

2016 9 9 2200 43.8 L 61.123 3.646 23.0 BER 52 0.6 3.6 3.7 3.7

2016 920 0736 58.5 L 76.954 23.179 19.7 BER 16 0.7 2.9 3.2 3.4

2016 930 0504 5.7 L 77.325 19.093 22.4 BER 17 0.9 2.8 3.4

2016 10 9 1248 28.2 L 62.428 2.179 29.0 BER 62 0.7 3.6 4.0 3.7

2016 1018 1109 1.6 L 77.188 17.585 15.0 BER 11 0.7 2.5 3.1

2016 1018 1224 11.5 L 77.190 17.742 20.6 BER 9 0.7 2.5 3.0

2016 1023 2042 2.9 L 76.976 18.624 23.0 BER 23 0.7 3.4 3.7 3.8

2016 1027 1022 15.8 L 70.694 -8.364 10.0 F BER 13 1.4 3.0

2016 11 1 1241 12.0 L 71.075 -7.572 0.0 BER 4 0.1 3.0

2016 11 3 1057 25.7 L 58.783 1.598 15.0 F BER 69 0.7 3.3 3.3 3.0 3.9BGS

2016 11 7 1125 50.0 L 77.746 20.338 15.0 F BER 6 0.6 3.1 3.2 2.9

2016 1110 0918 26.9 L 79.958 21.409 15.0 BER 7 0.6 2.5 3.0

2016 1229 0429 24.5 L 67.108 13.104 1.1 BER 10 0.6 3.2 3.3 4.0 3.3HEL


26

Figure 13. Seismogram of the two earthquakes felt at Svalbard in March 2016. The P-phases for the first

earthquake are marked.

Another significant earthquake occurred March 19th

at 21:55 (UTC) in the inner western part

of Bottenvika. Sweden. The University of Uppsala reported a magnitude ML(UPP)=4.1 and the

calculated magnitude from NNSN is ML(BER)=4.2.

Along the mid-Atlantic ridge a large number of earthquakes occurred with magnitude above

3. Of the 19 located earthquakes with calculated magnitude above ML=4.0, 13 were located

along the Mohns ridge and at the northern part of the Knipovich ridge. The magnitudes

calculated for earthquakes in the Norwegian-Greenland Sea are expected to be

underestimated.


27

With the mainland stations on the Lofoten, in Tromsø and Hammerfest, the network on Jan

Mayen, and stations on Bjørnøya, Hopen and Svalbard, the network detection capability in the

arctic area is relatively good. We define the arctic area as the region 65-85°N and 25°W-50°E.

Most of the activity falls into three areas: Jan Mayen, the Mid-Atlantic ridge and Storfjorden

southeast of Svalbard, as can be seen in Figure 14. Since 2014 data from Danish stations on

Greenland (see Figure 2) were included in the daily processing which has increased the

location capability for earthquakes west of Jan Mayen and northwest of Svalbard. The number

of earthquakes recorded on enough stations to be located, has increased.

Figure 14. Seismicity in the Norwegian arctic area during 2016. A total of 2027 located earthquakes.

4.3.1 Seismicity in Nordland

Figure 15 shows the seismicity in Nordland since 2000. The area includes the locations of

earthquake swarm activity such as Meløy (66.8N, 13.5E), Steigen (67.8N, 15.1E) and

Stokkvågen (66.3N, 13.1). The Steigen area was more active between 2007 and 2008, then it

was relatively quiet until 2015 when 44 earthquakes appeared. During spring 2016 the

temporary stations deployed during the NEONOR2 project were stopped. The decreased

station-density in the area has resulted in fewer events with low magnitude being located

(Figure 16).


28

Figure 15. Seismicity in the Nordland area. Blue circles show seismicity for 2016, red circles show

seismicity for 2000-2015, and yellow triangle is NNSN seismic stations. Only probably earthquakes are

included.

In the Jektvik (66.6N,13.5E) area there has been a decrease in seismic activity during 2016

compared to 2015 (Figure 16). During 2016, 295 earthquakes were located here, compared to

476 in 2015. The largest earthquake in the area occurred December 29th

, 2016 at 04:29 (UTC)

with a magnitude of ML(BER)=3.0. The earthquake was felt. The yearly distribution of

earthquakes located in the area is presented in Figure 18.


29

Figure 16 Time distribution (upper) and location (lower) of the earthquake swarm located in the Jektvik

area, southwest of the Svartisen glacier. Earthquakes occurring in 2016 are marked in blue. Note! The

events shown are limited by 66.5- 66.9N and 13.2-13.7E, a smaller area than show on the map. The

location of the permanent NNSN station (KONS) and the NEONOR2 temporary stations (N2VG, NBB13,

NBB 15, NBB17) are marked on the map.


30

Figure 17 The yearly number of the earthquakes in the area 66.5- 66.9N and 13.2-13.7E as seen in Figure

16.

4.3.2 Seismicity in the Jan Mayen area

Jan Mayen is located in an active tectonic area with two major structures, the Mid Atlantic

ridge and the Jan Mayen fracture zone, interacting in the vicinity of the island. Due to both

tectonic and magmatic activity in the area, the number of recorded earthquakes is higher than

in other areas covered by Norwegian seismic stations. During 2016 a total of 199 earthquakes

were located as seen in Figure 18 and of these, 6 had a magnitude equal or above 3.0. During

the fall of 2016 the digitizer used to register data from JNW and JNE started to malfunction.

The number of located earthquakes in the Jan Mayen area are therefore reduced, as can be

seen from the monthly distribution of earthquakes in Figure 18.

The largest earthquake in the Jan Mayen region in 2016 occurred on 3rd

September at 06:55

(UTC) and the magnitude is estimated to 4.2L(BER) and 5.4L(NAO). The earthquake is

located slightly southeast of the Beerenberg volcano and was felt by the personnel at Jan

Mayen. By the personnel at Jan Mayen the earthquake was described as

(http://jan.mayen.no/2016/09):

«Klokken 08.56 i morges merket de fleste på stasjonen at det begynte å riste.

Jordskjelvet var merkbart i rundt 30 sekunder og ble registrert av seismografene som vi har

rundt på øya.»


31

Figure 18. Earthquakes located in the vicinity of Jan Mayen during 2016. The time distribution is shown

in the upper part. The reduced seismic activity observed for the last part of 2016 might be due to a

malfunctioning digitizer.

The number of recorded earthquakes in the Jan Mayen area has varied over the last years

(Figure 19). The number of relatively strong earthquakes (M≥3) shows smaller time variation

than for the smaller earthquakes. The increases in 2004 and 2005 were due to the M=6.0

earthquake in 2004 and its aftershocks (Sørensen et al., 2007). The same is true for 2011,

where the M=6.0 earthquake on 29 January was followed by a sequence of aftershocks. The

30 August 2012 earthquake (M=6.3) with its fore and aftershocks clearly increases the

number of recorded events in 2012 compared with previous years, making it the largest

number of recorded events yearly for more than 10 years. For the following years after 2012,


32

the number of located smaller earthquakes has increased slightly, while the number of larger

(M≥3.0) earthquakes is relative stable.

0100200300

400500600700800900

1000

20012003

20052007

20092011

20132015

Total number of recordedearthquakes

Number of earthquakes withmagnitude larger or equal to 3

Figure 19. Yearly distribution of earthquakes located in the Jan Mayen area since 2001. The area is as

shown in Figure 18.

4.3.3 Seismicity at Svalbard

The seismicity in the Svalbard area is presented in Figure 20, showing both a map with the

seismicity since 2000 and the distribution of events over time. There are several seismically

active areas in this region. This report will focus on three main areas: the Storfjorden area

including Heer Land (on the northwest side of Storfjorden) and Diskobukta (the area west of

Egdeøya), Sørkappland (the area at the very southwest coast of Spitsbergen) and

Nordaustlandet. These will now be discussed in more detail.


33

Figure 20. Seismicity in the Svalbard area. Bottom: Earthquakes occurring in 2016 are plotted in red

circles. Yellow circles show seismicity for 2000-2015. The blue triangles give the station locations. Top:

Seismicity in the same area is plotted as latitude as function of time.


34

Storfjorden

The Storfjorden area southeast of Svalbard, defined by latitude 76.5-78N and longitude 16-

22E, has been more seismically active since the Mw=6.0 earthquake on 21 February 2008. The

earthquake was the starting point of a prolonged earthquake sequence. The yearly variation in

the number of detected earthquakes in Storfjorden area is shown in Figure 20. An increase in

the number of located earthquakes is clearly seen in 2008 explained by the M6 earthquake and

its aftershocks.

0

100

200

300

400

500

600

2003 2005 2007 2009 2011 2013 2015

M≥3.0

All earthquakes

Figure 21. Yearly number of earthquakes located to the Storfjorden area.

The increase in 2010 is mostly explained by an increase in the number of smaller earthquakes

as seen by the almost constant levels of earthquakes with M>3.0 since 2008. The better

detection was due to usage of the data from the Hornsund (HSPB) and Barentsburg stations,

from 2010 and 2012, respectively. A total of more than 39 earthquakes with magnitude larger

than M=4 have occurred in the area since 2008. There is a clear increase in 2016 related to

the activity in both Storfjorden and the Heer Land region. Heer Land has been seen to be

active in the past, going back to the 1970s.

The total number of events located in the Storfjorden area in 2016 was 505, which presents

an increase from 2015 when the corresponding number is 176. Figure 20 shows both a map

with the seismicity since 2000 and the distribution of events over time. One area where an

increase in seismic activity is clearly seen is Diskobukta (77.6-78.1N, 19.3-22.0E), where not

much seismicity had been seen previously. Searching in the NNSN database, there are only

located 12 earthquakes, with one of the reported magnitudes above 3.0, in this area. The first

located in 1996. Eight of these 12 earthquakes are recorded in 2016. During 2016, 121

earthquakes are located to this small area compared to 11 in 2015. The largest earthquake

occurred March 28th

at 10:32 (UTC) with a magnitude ML=5.2 (BER), followed 28 sec later

by a slightly smaller earthquake with ML=4.8. These earthquakes were felt throughout

Svalbard, and in Longyearbyen ‘Næringsbygget’ was evacuated.

In Svalbardposten 29.03.2016 one can read:

«Svalbard opplevde to rystelser tidlig tirsdag ettermiddag, den første cirka klokka 12.31, den

neste 20-30 sekunder etter. Inne i Post- og bankbygget, hvor Svalbardposten holder til, var

rystelsene merkbare, sammen med en slags buldring.


35

– Det var nesten som det smalt. Stolen flyttet seg 20-30 centimeter, forteller en kilde

Svalbardposten snakket med like etter.

I Næringsbygget valgte flere av de ansatte i Longyearbyen lokalstyre å evakuere bygningen i

noen minutter, og oppe i andre etasje i Coop begynte bordet å riste.

– Det var skikkelig ekkelt. Vi satt oppe og siste lunsj da bordet begynte å disse. Først forsto vi

ikke hva so skjedde, og noen tittet ut for å se om det var gått ras. Vi ble rent uvel, forteller

butikksjef Karin Mella.»

The main earthquake was followed by more than 40 aftershocks the next 28 hours, when the

activity slowly decreased as can be seen in Figure 22.

0

10

20

30

40

50

60

2015 2016 2017

Monthly number ofearthquakes

M≥3.0

Figure 22. Monthly distribution of earthquakes in Diskobukta. The peak is the 48 earthquakes located to

the area in March 2016.

Sørkappland

At Sørkappland, located at the southwestern coast of Spitsbergen (76.4-77.2N, 14-17E), the

earthquake activity has increased the last two years as can be seen from Figure 23.

0

10

20

30

40

50

60

70

2010 2011 2012 2013 2014 2015 2016

Yearly nunber ofearthquakes

M≥3.0

Figure 23. Yearly number of earthquakes recorded in the Sørkappland area.

The earthquakes located the last ten years are plotted in Figure 24. Digital data from the

seismic station at Hornsund, Svalbard (HSPB) was routinely included in the NNSN data

prosessing from November 2009. This increased the number of small earthquakes located to


36

the Sørkappland area. Since July 2015 there were 9 earthquakes with one calculated

magnitude above 3.0.

Figure 24. Earthquakes in the NNSN database since 2007. Note that for some time periods the location

capability might been reduced and the number of located small earthquakes are lower. The number of

larger earthquakes is expected to be reliable.


37

Nordaustlandet

Nordaustlandet is a well-known seismically active area. Earthquakes located since January

2007 are presented in Figure 25. In 2016, an independent small cluster developed to the west

of the regular activity on the western side of the Hinlopenstretet. It should be noted that the

location accuracy in this area is rather sensitive to the seismogram interpretation and small

changes may change the epicentre by tens of kilometers. However, the separation of this new

cluster from the regular pattern is likely to be real.

Figure 25. Earthquakes located at Nordaustlandet during 2016 (red) and between 2007-2015 (blue).

4.3.4 Earthquakes in the southern North Sea

During 2016, 14 earthquakes were detected and located in the North Sea as shown in

Figure 26 and listed in Table 10. The yearly distribution of earthquakes in the area is

presented in Figure 27. The largest of the events occurred on 3rd

November with a magnitude

of ML=3.3(BER) and ML=3.9(BGS). The earthquake was located using data from NNSN,

BGS, HEL and NORSAR.


38

Figure 26. Time distribution over time (upper) and location (lower) of the earthquake located within 54-

60N and 1W-5E in the southern North Sea (Note that the map is larger than the area used for selection of

earthquakes). Earthquakes recorded during 2016 are marked in red. Seismic stations are marked with

blue triangles.


39

0

5

10

15

20

25

30

20002001

20022003

20042005

20062007

20082009

20102011

20122013

20142015

2016

recorded earthquakes

M>3.0

Figure 27. Number of recorded earthquakes in the area 54-60N, 1W-5E.

Table 10. Earthquakes recorded during 2016 and located in the area limited by 54-60N and 1W-5E.

Year Date HRMM Sec L Latitud Long Depth AGA NST RMS ML MW ML(BGS)

2016 120 1859 21.0 L 58.916 1.366 8.6 BER 15 0.5 1.8 2.3

2016 121 1851 3.6 L 59.248 1.869 10.0 BER 16 0.9 1.6 1.9

2016 225 2208 32.9 L 58.909 1.327 16.4 BER 17 0.7 1.9 2.7 2.4

2016 3 7 2011 56.0 L 58.474 1.188 20.9 BER 18 0.6 1.6

2016 421 0122 31.3 L 58.953 1.408 29.6 BER 15 0.8 1.6 2.1

2016 422 0801 30.4 L 59.802 4.958 15.5 BER 12 0.5 1.4

2016 515 1731 8.1 L 59.813 2.448 15.0 BER 34 0.8 2.0 2.3

2016 624 2222 46.3 L 59.750 1.765 10.2 BER 22 0.8 1.8 2.3

2016 1029 1920 49.6 L 59.956 2.322 10.0 BER 34 0.6 2.0 2.4

2016 1031 1821 5.8 L 59.576 1.788 17.9 BER 26 0.4 2.1 2.1(NAO)

2016 11 1 1915 27.0 L 59.663 1.839 12.4 BER 9 0.6 1.5

2016 11 3 1057 25.7 L 58.783 1.598 15.0 BER 69 0.7 3.3 3.3 3.9

2016 1113 1448 6.7 L 59.030 1.757 13.6 BER 20 0.6 1.7

2016 1213 1458 26.5 L 58.217 0.979 21.6 BER 25 0.6 2.0 2.4


40

4.3.5 Felt earthquakes

In total, 14 earthquakes were reported felt and located within the target area during 2016 (see

Table 11 and Figure 28). For the Jan Mayen Island and the area southwest of the Svartisen

glacier, the number of felt earthquakes is expected to be larger than reported.

Figure 28. Location of the 14 earthquakes reported felt during 2016.

Large felt earthquakes are mostly reported to UiB shortly after the origin time, and location

information and questionnaires are available for the public on the site www.skjelv.no. Smaller

felt earthquakes may be reported by the public to local newspapers or other institutions and

then reported to UiB. Depending on the time-delay for these reports to be available at UiB,

the information on the web might be accordingly delayed. For any felt earthquake the public

has to be made aware of the questionnaire, which is done by informing on web and when UiB

is contacted by media, private persons or other institutions. Earthquakes large enough to be

felt and occurring in heavily populated areas increases the number of people using the web

reporting the intensities.

http://www.skjelv.no/


41

Table 11. Earthquakes reported felt in the BER database in 2016. Abbreviations are: ML = local

magnitude and Mw = moment magnitude, W: questionnaires received on web (Y/N). The largest felt

earthquakes are marked in red. Earthquakes marked in blue is not located in Norway. Due to technical

problems, earthquake no 13 is only recorded at JMIC and could therefore not be located.

Nr

Date

Time

(UTC)

Max.

Intensity

(MMI)

Magnitude (BER)

Instrumental

epicentre

location

W

1 11.02.16 10:41 IV ML=2.4, MW=2.8,

ML=2.6(NAO) 62.71N / 5.53E

2 19.03.16 21:55 V ML=4.2, MW=4.2,

ML=4.1(UPP) 65.03N / 22.55E -

3 29.03.16 10:32:10 V ML=5.2, MW=5.1 77.83N / 21.05E Y

4 29.03.16 10:32:38 V ML=4.8 77.74N / 20.67E -

5 10.04.16 04:31 III ML=2.2, MW=2.4,

ML=2.1(NAO) 62.22N / 5.79E N

6 20.04.16 16:01 IV ML=2.1, ML=2.0(NAO) 59.59N / 10.59E Y

7 10.06.16 04:06 IV ML=2.7, ML=2.5(NAO) 61.94N / 4.94E Y

8 17.07.16 21:12 III ML=1.1 62.16N / 5.99E N

9 28.08.16 07:07 II ML=1.5, ML=2.1(NAO) 67.21N / 14.56E N

10 03.09.16 06:55 III ML=4.2, Mb=5.1(EMSC) 71.08N / 7.98W N

11 22.09.16 07:43 IV ML=2.5 66.85N / 13.56E Y

12 10.10.16 22.07 II ML=2.0, ML=1.8(NAO) 61.66N / 4.56E N

13 28.10.16 17:50 IV - Jan Mayen N

14 29.12.16 04:29 IV ML=3.0, MW=3.3, ML=

4.0(NAO) 67.05N / 13.22E N

The largest felt earthquakes during 2016, are the earthquakes occurring 29th

March at 10:32

and 10:32:10 (UTC time). The magnitude 5.2 earthquake was followed by a slightly smaller

earthquake 28 sec later. These earthquakes were reported felt strongly at Svalbard (see section

4.3.3). The largest felt earthquake close to the Norwegian mainland occurred 29th

December.

This earthquake was felt in the Meløy area and was located offshore, slightly south-west of

Bodø.


42

5 Scientific studies

This section gives an overview of research work that is carried out under the NNSN project in

2016. The main objective of this work is to improve the understanding of earthquakes and the

seismological models in the region, mostly by using data recorded by the NNSN. Results will

be used to improve the NNSN monitoring service.

5.1 QLg tomography

By Andrea Demuth, UiB

We analyze the attenuation of Lg waves in Norway and adjacent areas. Attenuation is

described by the quality factor Q and is a basic parameter to characterize the crust and mantle.

Our goal is to gain a better understanding of the geological structures and tectonic processes

in Norway.

In a first step, we use spectral displacement amplitude ratios of Lg-waves and P-waves to

determine the lateral variation in wave attenuation in a frequency range of 2 Hz till 5 Hz. In

this approach, we assume that the main attenuation of the ratio is due to Lg wave attenuation.

Thus, lower ratios are interpreted as high Lg wave attenuation. We used all earthquakes

recorded by the NNSN since 1990, which have a local magnitude higher than 2.5 and

recordings by 4 or more stations. The ratio for one earthquake station pair was assigned to its

corresponding travel path.

Figure 29 Spectral displacement amplitude ratios of Lg-waves to P waves.

Figure 29 shows our Lg to P amplitude ratios for the areas in Norway with path coverage. It is

visible that Lg waves are higher attenuated in offshore areas than onshore. Furthermore, we

observe stronger attenuation in northern parts of Norway.

For a more detailed analysis of the Lg attenuation in Norway, we only use spectral

displacement amplitude decay of Lg waves to derive the corresponding quality factor. This is

done in a tomographic approach. The tomographic code is built on the theory of Barmin et al.


43

2001. The code inverts for source and site terms of each observed source receiver pair as well

as for the quality factor. This is done with a damped least square approach. Additionally we

implemented a spatial smoothing matrix. In order to test the code, we generated a checker

board test and used our real source receiver configuration Figure 30a.

Figure 30 (a) Synthetic QLg checker board input model with real path coverage (black lines). Light blue

triangles represent stations and dark blue stars earthquakes. (b) Inversion result for QLg with the new

derived tomographic code.

The checkerboard pattern is well resolved in areas with high path coverage (Figure 30 b). In

areas with low to no coverage the Q value is set to the background value of 400. We observe

some smearing on the edges of the path covered areas. The input values for the source terms

and site terms alternate in a checker board pattern as well and are well resolved.

The next step is to run the tomographic code with the real amplitude values for various

frequencies. In order to do that, an average QLg value is first determined which is used as

starting value for the inversion. The average QLg values for various frequencies are going to

be used to find a general frequency dependence of QLg for Norway.

5.2 Relocation of seismicity in southern Norway and the North Sea using a

Bayesian hierarchical multiple event location algorithm

By Steven Gibbons, NORSAR

We are continuing our reassessment of seismicity in and around southern Norway involving a

critical re-evaluation of waveform data and arrival picks, exploitation of as yet unused seismic

data, and application of a probabilistic multiple event location algorithm. We have been

combining datasets from NORSAR, the University of Bergen, additional regional networks

(for example Denmark, the Netherlands, and the United Kingdom), and – in a few exceptional

cases – teleseismic data. For each event, a preliminary location estimate is made using the

extended set of seismic arrivals; phases with significant time-residuals, or other indications of

poor quality, are removed. The cleaned sets of arrivals are then processed by the Bayesloc

multiple event location program (https://www-gs.llnl.gov/about/nuclear-threat-

reduction/nuclear-explosion-monitoring/bayesloc) which has been demonstrated to provide

enhanced epicenter distributions for clustered seismicity on both regional and global scales.

https://www-gs.llnl.gov/about/nuclear-threat-reduction/nuclear-explosion-monitoring/bayesloc

https://www-gs.llnl.gov/about/nuclear-threat-reduction/nuclear-explosion-monitoring/bayesloc


44

In classical single-event location algorithms, the traditional measure of uncertainty is an error

ellipse calculated from the formal uncertainties surrounding the arrival times used in the

inversion. Systematic bias in the applied velocity models is often not accounted for and event

location estimates are frequently presented with unrealistically small error ellipses. Bayesloc

calculates joint probability distributions both for hypocenters and parametric information for

multiple events simultaneously. In providing implicit corrections to traveltime estimates,

Bayesloc can be demonstrated to provide more realistic estimates of location uncertainty. For

example, an event for which the applied velocity model provides a poor representation of the

traveltimes may have a large formal error ellipse due to the high residuals. The uncertainty

indicated by Bayesloc may be significantly smaller if these traveltimes are correctly

calibrated. Similarly, an event with very few observations may have a very small formal error

ellipse, since there exists a location for which these few constraints can be satisfied very

precisely. Bayesloc searches a huge parameter space using a Markov Chain Monte Carlo

algorithm and can identify that such event locations have a very broad probability

distribution. The attributed uncertainty is consequently far larger for the poorly constrained

events.

A current snapshot of the multiple event probability distribution is shown in Figure 31. This

indicates at a glance those events which appear very well constrained – and these appear to

cluster in distinct structures – and those events with poorer constraints which may need a

reassessment of the associated seismic data. The dataset is being increased continually and

special attention is being paid to events which may have far tighter prior constraints. These

may be due to large magnitudes (hence recorded on a far greater number of stations) or events

that have been very tightly constrained by temporary deployments. A feature of Bayesloc of

special interest for this dataset is the probabilistic attribution of phase identifications. In

classical event location, a phase might be attributed a label which doesn’t actually correspond

well with the true path traveled from source to receiver. We provide Bayesloc with multiple

path models and, in the case of erroneous phase identification, Bayesloc will attribute a higher

probability to those solutions with the correct phase identification – rather than derailing the

location estimate by forcing the error on the final solution.


45

Figure 31. Epicenter estimates for around 300 seismic events in and around southern Norway between

1992 and 2016 located using the Bayesloc program. The blue triangles indicate the locations of permanent

seismic stations of the Norwegian National Seismic Network, the NORSAR and Hagfors seismic arrays,

station MUD of the Danish national network, and temporary stations of the MAGNUS and NEONOR

deployments. Bayesloc returns a joint probability distribution of event locations, corrections to traveltime

estimates, precision of arrival-time estimates, and phase labels. For each event, the center of the

probability distribution is displayed together with the lateral standard deviation; the darkest symbols

indicate the events with the best constrained

5.3 Testing of a method for distinguishing between earthquakes and

explosions

By Ilma Janutyte, NORSAR

We have continued testing of a method which helps to objectively distinguish between

earthquakes (EQs) and explosions (Janutyte, 2017). The method was first developed at the

Institute of Seismology, University of Helsinki, Finland (Kortström et al., 2016), and is

successfully used there to help in the daily data analysis. During this reporting period we have

made a reevaluation of the method for the stations FOO and HYA using an extended dataset

as well as using different partitioning of the training and validation data. In addition, we have

applied the method to datasets at the stations LOF and MOR8 in northern Norway. The

datasets for the stations were compiled from the University of Bergen (UiB) catalogs, and we

made attempts to obtain examples of both EQs and explosions originating in different


46

directions from the selected stations. The limit for distance was from 15 to 270 km (Figure

32).

A B

Figure 32. Seismic events used to develop and verify the reference spectral models for the stations:

A) HYA and FOO in the south, and B) LOF and MOR8 in the north. The seismic events are marked as

circles and stars, while the seismic stations are marked as green triangles.

The results are shown in Figure 33 and Table 12. The prediction shows possible EQs as

positive values and possible explosions as negative values. The more the value is positive, the

more it tends to be the EQ-like, while the more the negative, the more the explosion-like,

while around the zero the prediction is weaker and uncertain.

The test case for FOO and HYA stations in the south shows prediction precision of 100 %, i.e.

all the seismic events both EQs and explosions were evaluated as correct. For LOF and

MOR8 stations in the north the testing precision is 83 and 87 %, respectively. This might be

due to too small datasets and not a sufficient number of training examples for the reference

model. Especially for LOF station the total number of reference explosions available in the

bulletin is low.

Table 12. Number of seismic events used in the study for obtaining (training) and validation (testing) of

the spectral reference models, and the obtained reference model precision (error) and precision of the test

dataset (test precision).

Station

code

in total training

dataset

testing

dataset model

error [%]

test

precision

[%] EQ EX EQ EX EQ EX

FOO 73 57 58 47 15 10 35 100

HYA 82 148 55 108 27 40 21 100

LOF 89 26 69 23 20 3 49 83

MOR8 78 58 58 47 20 11 30 87


47

A B

C D

Figure 33. Predictions using the validation datasets for the different reference models:

A) for HYA station EQ data are up to event number 27;

B) the common events for FOO and HYA stations; EQ data are up to event number 15;

C) for MOR8 station EQ data are up to event number 21;

D) the common events for LOF and MORB stations; EQ data are up to event number 21.

5.4 Towards the integration of NNSN stations in automatic network event

location

By Steven Gibbons, NORSAR

Network detection at NORSAR of seismic events in Fennoscandia has for many years been

performed by the Generalized Beamforming (GBF) method (Ringdal and Kværna, 1989) in

which phase arrivals on seismic arrays are associated based upon rules relating to the arrival

times and other parameters such as the backazimuth and the apparent velocity. This system

has not so far been able to utilize many of the high quality seismic signals on 3-component

stations in the region like those from the NNSN network. A significant effort is now being

made to run detectors at low detection threshold on the NNSN 3-component stations, and to

generate output which can be utilized by the GBF process.

In a study aimed at detecting and locating aftershocks following major earthquakes, Gibbons

et al. (2016) demonstrated considerable success using a detection statistic based upon a

continuous calculation of the Auto Regressive Akaike Information Criterion (AR-AIC). The

high frequency content of regional signals in Fennoscandia makes this method attractive for

the detection of regional P-phases (see the uppermost two traces of Figure 34). The detection

statistic attains local maxima very close to the best manual estimates of the signal onset and,

once a detection has been declared, the backazimuth and apparent velocity are estimated using

polarization analysis. Work is now being carried out on optimizing the detection of S-phases.


48

Given a good estimate for the backazimuth of the P-arrival, the horizontal traces are rotated to

optimize the Signal-to-Noise-Ratio (SNR) of the expected S-arrival and the traces are

bandpass-filtered in a generic frequency band. A corresponding AR-AIC trace is calculated on

which the S-phase is detected (see the lowermost two traces of Figure 34), and detection lists

are written out with arrival times and associated parameters. Initial results are highly

encouraging although a significant effort will be required on a number of issues, for example

the automatic discrimination of signals from regional earthquakes and signals from local

(noise) disturbances.

Figure 34. Detection of regional P- and S- waves from a low-magnitude seismic event on station SKAR of the Norwegian National Seismic Network using an Auto Regressive-Akaike Information Criterion detection procedure.

6 Publications and presentations of NNSN data during 2016

Data collected on Norwegian seismic stations are made available through the Internet and is

provided on request to interested parties. Therefore it is difficult to get a comprehensive

overview on the use and all publication based on Norwegian data. The following reference list

shows publications and presentations of UiB and NORSAR scientists for the reporting period,

based on data of NNSN and NORSAR stations.


49

6.1 Publications

Havskov, J., Sørensen, M.B., Vales, D., Özyazicioglu, M., Sánchez, G. and Li, B. (2016).

Coda Q in Different Tectonic Areas, Influence of Processing Parameters,

Bulletin of the Seismological Society of America, vol 106(3),

doi: 10.1785/0120150359.

Schweitzer, J.: NORSAR and the seismic monitoring of the European Arctic

The Norwegian Scientific Academy for Polar Research (NVP),

Newsletter, 19, May 2016, 7 pp

Gibbons, S. J., G. Antonovskaya, V. Asming, Y. V. Konechnaya, E. Kremenetskaya,

T. Kværna, J. Schweitzer, N. V. Vaganova:

The 11 October 2010 Novaya Zemlya Earthquake: Implications for Velocity

Models and Regional Event Location

Bull. Seism. Soc. Amer., 106, (4), 1470-1481, 2016, doi: 10.1785/0120150302

Köhler, A., C. Nuth, C. Weidle, J. Kohler, E. Berthier, J. Schweitzer:

A fifteen-year record of frontal glacier ablation rates estimated from seismic data

Geophys. Res. Lett., 43, (23), 12,155-12,164, 2016, doi: 10.1002/2016GL070589

6.1 Master degree thesis, UiB

Igland, Kristoffer: Spatio-temporal evolution of earthquake swarms in the Nordland area of

Norway. MSc thesis, Dept. of Earth Science, UiB, June 2016.

6.2 Oral presentations

Antonovskaya, G., Y. Konechnaya, I. Basakina, J. Schweitzer, A. Fedorov: Seismological

investigation of lithosphere processes in the European Arctic 35th General Assembly,

ESC, Trieste, 4 - 10 September, 2016

Antonovskaya,G., J. Schweitzer: Seismological research related to geophysical processes in

the European Arctic RFBR-RCN workshop, 23 - 24 November 2016, St. Petersburg,

Russia

Bellwald, B., Hjelstuen B.O., Sejrup, H.P., Stokowy, T., Kuvås.

Holocene Mass Transport Deposits in Western Norwegian fjords and lakes

revealing prehistoric earthquake history of Scandinavia.

AGU Fall Meeting 2016, San Francisco, United States of America.

Bellwald, B., Hjelstuen B.O., Sejrup, H.P., Stokowy, T., Kuvås, J., 2016.

Spatio-temporal Holocene earthquake patterns of Norway revealed by


50

subaquatic mass movements.

Geofaredagen. Geofaredagen 2016, NGU, Trondheim, Norway, October 2016.

Bellwald, B., Hjelstuen, B.O., Sejrup, H.P., Stokowy, T., Kuvås, J. 2016.

Prehistoric earthquake history of Scandinavia revealed by Holocene Mass Transport

Deposits in Western Norwegian fjords and lakes.

4th Annual Workshop of Glaciated North Atlantic Margins (GLANAM), Coleraine,

Northern Ireland, June 2016.

Demuth, A., L. Ottemöller and H. Keers, Lg wave attenuation tomography for Norway, 35th

General Assembly, ESC, Trieste, 4 - 10 September, 2016.

Köhler, A., C. Nuth, J. Schweitzer, C. Weidle, J. Kohler, G. Buscaino, E. Berthier:

Quantification of glacier calving through seismic monitoring at Kronebreen,

Svalbard.

NORRUSS Project GEOPROC Workshop, 21 - 25 November, 2016,

St. Petersburg, Russia

Janutyte, I., L. Ottemöller, J. Michalek, C. Lindholm, J. Schweitzer, S. J. Gibbons,

T. Kværna: 3-D velocity model for Norway on-shore and off-shore

Geophysical Research Abstracts, 18, EGU2016-5505, 2016,

EGU General Assembly 2016

Kim, W.-Y. and L. Ottemöller, Regional Magnitude Scale for Earthquakes along

Spreading Ridges and Transform Faults in Arctic Zone, Norway, 35th General

Assembly, ESC, Trieste, 4 - 10 September, 2016.

Michalek, J, L. Ottemöller, I. Janutyte and C. Lindholm: Usage of SH/P amplitude ratios

for focal mechanism determination - case study from the Nordland region,

Norway, 35th General Assembly, ESC, Trieste, 4 - 10 September, 2016.

Minakov, A., J. Schweitzer, J. I. Faleide: Lithospheric structure in NW Barents Sea

from travel-time modeling of shot recordings on SPITS.



Ottemöller, L., W.-Y. Kim, W. Dallmann and F. Waldhauser, Storfjorden Earthquake

Sequence: 2008-2016, 35th General Assembly, ESC, Trieste, 4 - 10 September, 2016.

Schweitzer, J.: Regional Seismic Event Location

1st General Assmebly, African Seismological Commission,

Nile, Egypt, April 2016

Schweitzer, J., Y. Konechnaya, A. Fedorov, S. Gibbons, M. Pirli:

A 23 year-long seismic bulletin for the European Arctic

35th General Assembly, ESC, Trieste, 4 - 10 September, 2016

Schweitzer, J., Y. Konechnaya, A. Fedorov, S. Gibbons, M. Pirli: The most complete

seismic bulletin for the European Arctic between 1990 and 2016



51


Sørensen, M.B.: Natural Hazards in the Arctic,

Presentation at 2nd Ocean Flagship Workshop, October 2016.

Sørensen, M.B.: Jordskjev i Norge.

Presentation at "Kunnskapsløft Bølgen", Stranda, 17-18 March 2016

Sørensen, M.B.: Tsunamier i Norge - og resten av verden.

Presentation at "Kunnskapsløft Bølgen", Stranda, 17-18 March 2016

6.3 Poster presentations

Gibbons, S.J., Trine Dahl-Jensen, Tormod Kværna, Tine B. Larsen, Berit Paulsen,

and Peter Voss: Relocating Seismicity on the Arctic Plate Boundary Using

Teleseismic and Regional Phases and a Bayesian Multiple Event Locator.

(Poster at EGU 2016)

Janutyte, I., L. Ottemöller, J. Michalek, C. Lindholm, J. Schweitzer, S. J. Gibbons,

T. Kværna: 3-D velocity model for Norway on-shore and off-shore

13th EGU General Assembly, Vienna, April 2016 (poster)

Köhler, A., C. Nuth, J. Schweitzer, G. Buscaino, C. Weidle: Quantification of glacier

frontal ablation through passive seismic monitoring at Kronebreen, Svalbard

35th General Assembly, ESC, Trieste, 4 - 10 September, 2016 (poster)

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