coquimbo educational slides earthquacke 2015

8/15/2019 Coquimbo Educational Slides Earthquacke 2015

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Seismotectonics

The September 16, 2015 M 8.3earthquake occurred ~ 7 kmoffshore of Central Chile, as aresult of thrust faulting on theinterface between the Nazcaand South America plates. Atthe latitude of this event, theNazca plate is moving towardsthe east-northeast at a velocity

of 74 mm/yr with respect toSouth America, and begins itssubduction beneath thecontinent at the Peru-ChileTrench, 85 km to the west ofthe September 16 earthquake.The size, location, depth (~26km) and mechanism of thisevent are all consistent withits occurrence on themegathrust interface in thisregion.

C h i l e

A r g e n t i n a

P e r u

- C h i l

e T

r e n c

h


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Slip (m)

0

4

8

12

16

20

EQs, 1900-present

EQs, 1971

EQs, 1985

EQs, 2010

EQs, 09-2015

1922

1943

1971

2010

1985

2015

A Century of LargeEarthquakes in Central Chile

Chile has a long history of massiveearthquakes, including the 2010 M8.8 Maule earthquake in CentralChile, which ruptured a ~400 km longsection of the plate boundary south ofthis 2015 event (and to the south of

the Juan Fernandez Ridge, whichenters the trench immediately southof the 2015 earthquake). Over thecentury prior to the September 16,2015 earthquake, the region within400 km of this event has hosted 15

other M 7+ earthquakes including theM 8.0 and M 7.5 1985 Valparaisoearthquakes. This subduction zonealso hosted the largest earthquake onrecord, the 1960 M 9.5 earthquake insouthern Chile.

J u a n F e r n a n

d e z R i dg e


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0−80 −40 0 40 80 120 160 200 240 280 320 360 400 440 480 520 560 600 640 680

Nazca - South

America Plate

Interface

The 2015 Coquimboearthquake occurred onthe plate interface between the Nazca andSouth America Plates.Rupture occurred nearthe Peru-Chile trench,the surface expressionof the plate boundary.

The mainshockhypocenter is inagreement with the Slab

1.0 modeled plateinterface (blue line). Thered line (top) shows aschematic of the plate boundary which bettercaptures the flat slabnature of subduction in

this region.

Nazca Plate South America Plate

A A'

A' A

Mainshock

hypocenter

Slab 1.0

D e p t h ( k m )

D e p t h ( k m )

No. Earthquakes


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Earthquake Twitter Detection (@USGSTed)

Twitter detectionissued to NEIC in ~45sec after origin time

Initial instrumentalearthquake location in99 sec

Collected 85,000"earthquake" tweets(“terremoto” or“temblor”) in the firsthour

Large ratio of“terremoto” to“temblor” tweetsquickly indicated alarge earthquake


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Earthquake Notification

https://twitter.com/USGSted

http://earthquake.usgs.gov/earthquakes/feed/v1.0/ http://earthquake.usgs.gov/earthquakes/map/

Updated

Alert

10 Minutes Later

https://twitter.com/USGStedhttp://earthquake.usgs.gov/earthquakes/feed/v1.0/http://earthquake.usgs.gov/earthquakes/map/http://earthquake.usgs.gov/earthquakes/map/http://earthquake.usgs.gov/earthquakes/feed/v1.0/https://twitter.com/USGSted


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ShakeMap Intensity

DYFI = circle; Instruments = triangles

Instrumental

Did You Feel It? (DYFI)


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Did You

Feel It?(DYFI)

75˚W 70˚W 65˚W

35˚S 35˚S

30˚S 30˚S

OFFSHORE COQUIMBO, CHILEUSGS Community Internet Intensity Map

Sep 16 2015 06:54:33 PM local 31.5695S 71.6543W M8.3 Depth: 25 km ID:us20003k7a

Processed: Sat Sep 19 00:10:05 2015

Santiago

Cord

Mendoza

Tucuman

San Juan

Santiago d

Talcahuano

Rancagua

Talca

Catamarca

Rio Cu

Los angeles

Coquimbo

La Rioja

Copiapo

Mercedes

Santa

Ovalle

Linares

Vallenar

Chimbarongo

1147 responses in 17 ZIP codes and 111 cities (Max CDI = IX)

CITY SIZE

2M+

100,000+10,000+ 1000 Responses

• Largest nearbyreported intensity ofIX

• Moderate shaking(V) reported inSantiago

Metropolitan Area


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M 8.3, OFFSHORE COQUIMBO, CHILEOrigin Time: Wed 2015-09-16 22:54:33 UTC (19:54:33 local)

Location: 31.57oS 71.65

oW Depth: 25 km

PAGERVersion 8

Estimated Fatalities Estimated Economic Losses

Created: 23 hours, 17 minutes after earthquake

Estimated Population Exposed to Earthquake ShakingESTIMATED POPULATION

EXPOSURE (k = x1000)- -* - -* 595k* 6,455k* 3,052k* 794k 126k 0 0

ESTIMATED MODIFIEDMERCALLI INTENSITY

PERCEIVED SHAKING Not felt Weak Light Moderate Strong Very Strong Severe Violent Extreme

POTENTIALDAMAGE

ResistantStructures

VulnerableStructures

none

none

none

none

none

none

V. Light

Light

Light

Moderate

Moderate

Moderate/Heavy

Moderate/Heavy

Heavy

Heavy

V. Heavy

V. Heavy

V. Heavy

*Estimated exposure only includes population within the map area.

Population Exposure population per ~1 sq. km from Landscan

Orange alert level for economic losses.Significant damage is likely and the disaster ispotentially widespread. Estimated economiclosses are less than 1% of GDP of Chile. Pastevents with this alert level have required aregional or national level response.

Yellow alert level for shaking-related fatalities.

Some casualties are possible.

Structures:Overall, the population in this region resides

in structures that are resistant to earthquakeshaking, though some vulnerable structuresexist. The predominant vulnerable buildingtypes are low-rise reinforced/confinedmasonry and adobe block construction.

Historical Earthquakes (with MMI levels):

Date

(UTC)

Dist.

(km)

Mag. Max

MMI(#)

Shaking

Deaths

1973-10-05 168 6.7 VIII(2k) 0

1997-10-15 90 7.1 VIII(3k) 7

1985-03-03 174 7.9 VII(7,023k) 177

Recent earthquakes in this area have causedsecondary hazards such as tsunamis,landslides, and liquefaction that might havecontributed to losses.

PAGER content is automatically generated, and only considers losses due to structural damage.Limitations of input data, shaking estimates, and loss models may add uncertainty.

http://earthquake.usgs.gov/pager

FOR TSUNAMI INFORMATION, SEE: tsunami.gov

Event ID: us20003k7a

Selected City Exposurefrom GeoNames.org

MMI City Population

VIII Illapel 23k

VIII Ovalle 77k

VII Monte Patria 14k

VII Salamanca 13k

VII La Serena 155k

VII Vicuna 13k

V Santiago 4,837k

V Vina del Mar 295k

V Valparaiso 282k

V Puente Alto 510k

V Mendoza 877kbold cities appear on map (k = x1000)

Prompt Assessment of

Global Earthquakes for

Response (PAGER)

• Median loss estimation:- 60 fatalities- $650M economic

loss

• Chilean Red Cross reported13 fatalities

• AIR Worldwide estimatesinsured losses at $600-$900M

• La Oficina Nacional de

Emergencia del Ministeriodel Interior y SeguridadPública (ONEMI) reportedmore than 400 residential buildings were destroyedand 700 residential buildings sustained majordamage


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Slip (m)

Finite Fault Model (FFM)

• M 8.3 mainshock on 9-16-2015• 46 km W of Illapel, Chile• 229 km NNW of Santiago, Chile

• Rupture initiated on the subductionzone interface at a depth of about 26km and ruptured mostly up dip towardthe Peru-Chile trench

• Slip of >6 m occurred on the shallow

portion of the interface near the Peru-Chile trench

• Source duration of ~140 sec

Nazca Plate

P e r u

- C h i l

e T

r e n c h

South America Plate

Illapel

Valparaiso

Santiago


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Single Source

W-Phase Analysis

• Preferred single source W-phase solution consists of aMw 8.3 thrust faulting event

• The size, location, depth andmechanism of this event areall consistent with itsoccurrence on the

megathrust interface

• Two distinct pulses in themoment rate functionindicate unmodeledcomplexity in the single

source solution!" $%&

'()*+,-. *-/( .(0123 4&5

61078.9+1*-,)3 4&5

:(;*/

φ ? &4&δ = 19λ = 83

Pulse 2

Pulse 1


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837%-@-=0 #A 837%-@-=0 !A

B: CD!

E-=0/6?F 0?G- F-*+>A !";H+*I%F3/+0?6=A !";

5-,01A J"D$ 4G

φ K L$"D'δ = 20.3λ = 106.2

B: MD!

E-=0/6?F 0?G- F-*+>A $!;H+*I%F3/+0?6=A J$DCJ'M;

5-,01A !LD$ 4G

φ K L$CD'Nδ = 22.9ºλ = 87.5º

!"#$%&'(#%$) O1- 0?G- F-*+> +=F 1+*I%F3/+0?6= 6I 01- I?/;0 ;37%-@-=0 P-/-

I?Q-F +0 !" ;-9D RG+091?=S 01- G6G-=0 /+0- I3=90?6=T +=F 01- F?, 6I 01- I?/;0;37%-@-=0 P+; I?Q-F +0 !"DLND

Multiple Source

W-Phase Analysis

• Complex ruptureinvolving 2 distinctpulses of moment release

• Initial M 7.2 rupture at adepth of about ~40 kmoccurred in the 1st 20+ s

• Followed by ~80+ s ofM 8+ up-dip megathrustrupture


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Slip (m)

0 10 20 30 40 50 60 70 80 90 100Earthqauke Depth (km)

Multiple

Event

Aftershock

Relocations

• Depthsconstrained from waveformmodeling(Wphase, RMT,etc.) whenpossible (coloredcircles).

• Mainshock andaftershocksrelocate ~5-10 km

W-NW of the singleevent locations

• Seismicity largelyabsent in FFM’sregion of largestslip

Relocated Aftershocks compared to FFM Relocation Vectors


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!74˚ !73˚ !72˚ !71˚ !70˚ !69˚

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!CFS (MPa)

Coulomb Stress Change

From Mainshock

•

Predicted Coulomb stress changefrom finite fault model

• Coulomb stress change is a measureof how much a fault is brought closerto (red) or farther from (blue) failing

• Background colors show Coulombstress change resolved on thesubduction plate boundary

• Coulomb stress change is alsoresolved onto earthquake fault

planes at their relocatedhypocenters; these events areplotted and colored by the Coulombstress change


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!74˚ !73˚ !72˚ !71˚ !70˚ !69˚

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2 m

4 m

6 m

TOLO

PEDR

CMBA

LVIL

Observed

Predicted50 cm

CSN StationsPredicted vs

Observed Horizontal

GPS Displacements• Predicted horizontal displacement

from teleseismic finite fault model

• Red arrows indicate predictedhorizontal displacement from finite

fault model

• Black arrows indicate horizontaldisplacements observed at GPSstations

Data Source:University of Chilehttp://www.csn.uchile.cl/desplazamientos-del-terremoto-de-illapel-2015/


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Observed InSAR vs Predicted from Teleseismic FFM

InSAR uses satellite images to measure

ground displacement

Observed Predicted

D t C dit


17/18

Geodetic Fault Slip Model Data Credit: Advance Rapid Imaging

and Analysis (ARIA)Center for Natural

Hazards, NASA

University of MissouriUniversity of Chile


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−76˚ −74˚ −72˚ −70˚

−36˚

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Slip (m)

0

4

8

12

16

20

EQs, 1900-present

EQs, 1971

EQs, 1985

EQs, 2010

EQs, 09-2015

1922

1943

1971

2010

1985

2015

Summary Mw 8.3 earthquake is on a shallow anglethrust fault within the subduction zoneplate boundary between the Nazca and

South America plates

Rupture initiated at a depth of about 26 km withlargest rupture (> 6 m) occurring up dip (west),toward the Peru-Chile trench

Aftershocks are primarily in regions adjacent to thearea of maximum earthquake slip and down dip (east)of the main fault rupture

The Mw 8.3 earthquake occurred within the rupturezone of the 1943 M8.1 earthquake and into thepossible rupture zone of the 1971 M 7.8 earthquake to

the south. It is adjacent to the 1922 M8.5 and 1985M8.0 rupture zones, to the north and south,respectively

The South American subduction zone hosts asignificant number of large earthquakes that provide

details on strain accumulation and release during theearthquake cycle

coquimbo educational slides earthquacke 2015

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