CTBT Related Activities of Turkish National Data Center Nurcan Meral Ozel, Ocal Necmioglu, Korhan U. Semin, Serdar Kocak, T. Cem Destici, Ugur Teoman

contact: ozeln@boun.edu.tr

Bogaziçi University, Kandilli Observatory and Earthquake Research Institute (KOERI) CTBT: Science & Technology 2011, Vienna, AUSTRIA

Introduction

Turkish National Data Center and Belbasi Nuclear Tests Monitoring

Center

Bogazici University - Kandilli Observatory and Earthquake Research Institute (KOERI)

is acting as the Turkish National Data Center (NDC) and responsible for the operation of

the International Monitoring System (IMS) Primary Seismic Station (PS-43) under

Belbasi Nuclear Tests Monitoring Center for the verification of compliance with the

Comprehensive Nuclear-Test-Ban Treaty (CTBT). The NDC is responsible for operating

two arrays which are part of the International Monitoring System (IMS), as well as for

transmitting data from these stations to the International Data Centre (IDC) in Vienna. ).

The NDC is sharing the responsibility with U.S. Air Force Technical Application Center

(AFTAC) for the operation and maintanence of two arrays in central Anatolia.

The Nuclear Test conducted by North Korea on 25 May 2009 has also been recorded by

the PS-43 array and the signal has been evaluated by the Turkish NDC.

25 May 2009 North Korean Nuclear Test Analysis

On 25 May 2009, The Democratic People’s Republic of Korea (DPRK) claimed that it had conducted

a nuclear test. Corresponding seismic event was recorded by IMS and IDC released first automatic

estimation of time (00:54:43 GMT), location (41.2896 º N and 129.0480 º E) and the magnitude (4.52

mb) of the event in less then two hours time (USGS: 00:54:43 GMT; 41.306°N, 129.029°E; 4.7 mb).

(Figure 2, Map produced by IDC)

During our preliminary analysis of the 25th May 2009 DPRK event, we saw a very clear P arrival at

01:05:47 (GMT) at BRTR SP array. The result of the f-k analysis performed in Geotool software was

also indicating that the arrival belongs almost certainly to the DPRK event. After the interactive

analysis by IDC, Reviewed Event Bulletin (REB) was published and we have observed that BRTR

arrival was manually picked by analyst and associated to the DPRK event in REB. When comparing

our f-k results (calculated at 1-2 Hz) with REB, however, we have noticed that our calculation and

therefore corresponding residuals (calculated with reference to REB residuals) are much better in

comparison to REB, despite the fact that we performed f-k only once, i.e. we did not even try to

improve the f-k results.

Co-operation with IDC

IDC reported that there was indeed an automatic detection at 01:05:47.950 with a high slowness value

of 33.11 sec/deg, which led the detection to be classified as S-type signal, and that was the reason why

the arrival was not used by automatic network processing. This problem was resolved by the IDC

Analyst during interactive analysis, during which the detection was renamed as P and was associated

correctly to the event. This arrival was, however, a second S-type arrival observed within a priori set 2-

4 Hz beam. If the frequency band would have been changed to 1-2 Hz as the Turkish NDC did, then

this S-type arrival disappears and correct f-k solution occurs. According to IDC, new azimuth or

slowness values (f-k parameters) should be determined when possible if an arrival is manually added

by Analyst, or if the azimuth and slowness attributes will contribute substantially to the precision of an

event hypocenter, or if the azimuth and slowness residuals exceed limits set by IDC Analysis

guidelines and procedures. These guidelines help to minimize the time required to analyze events.

Therefore, the f-k parameters released in the REB for a given arrival are not necessarily the best

possible results. This will inevitably result in relatively less effort being devoted to individual arrivals

for those events that are well constrained by large numbers of associated phases such as the DPRK

event .

Figure 2: Location of the North Korean events by IDC

Participation to NDC Evaluation Workshops

As Turkish NDC, we actively participate in this annual workshop since 2008, in order to obtain

feedback from experts of other National Data Centers (NDCs), as customers of the

Provisional Technical Secretariat (PTS), on the performance of the verification system in order to

foster its continual improvement and on the set of Key Performance Indicators (KPIs) which would

best represent and measure such performance.

NDC Preparedness Exercise (NPE)

At the 2006 NDC Evaluation Workshop in Kiev, Ukraine, it was recognized that a limited

event analysis exercise performed by interested NDCs would contribute to the PTS product

evaluation process and to the assessment of processing and analysis procedures applied at

NDCs.

The aim of this exercise can be summarised as follows,

- Evaluation of the effectiveness of analysis procedures applied at NDCs with respect to

event location, magnitude determination, event discrimination and identification.

- Evaluation of the usefulness and completeness of the IDC products such as SEL1, SSEB, REB.

- Testing of data flow between IDC and NDCs.

Belbasi Array

The Belbasi array was established in 1951, as a four-element (Benioff 1051) seismic

array as part of the United States Atomic Energy Detection System (USAEDS). Turkish

General Staff (TGS) and U.S. Air Force Technical Application Center (AFTAC) under the

Defense and Economic Cooperation Agreement (DECA) jointly operated this short

period array. The station was upgraded and several seismometers were added to array

during 1951 and 1994 and the station code was changed from BSRS (Belbasi Seismic

Research Station) to BRTR-PS43 later on.

Technical Specifications PS-43 is composed of two sub-arrays (Ankara and Keskin): the medium-period array

with about 38 km diameter located in Ankara and the short-period array with a 3 km

diameter located in Keskin. Each array has a broadband element located at the middle of

the circular geometry. Short period instruments are installed at depth 30 meters from the

surface while medium and broadband instruments are installed at depth 60 meters from

surface.

Figure 4: Analysis of the 25 May 2009 North Korean event by Turkish NDC Figure 2: Location and configuration of Ankara and Keskin Arrays (BRTR- PS43)

Conclusion

Turkish NDC (National Data Center) and Belbasi Nuclear Tests Monitoring Center is actively

involved in CTBTO affairs. 25 May 2009 North Korea event analysis is a good example of

cooperation with CTBTO. The forthcoming NDC Preparedness Exercise 2010 (NPE10) differs to the

first three exercises.This time an fictitious release of radionuclides will be the trigger scenario of the

exercise and all verification technologies have to be included in the data analysis. As Turkish NDC

we will pariticipate in this exercise with a presentation.