Uncertainty of location and multiple-point source model of

M 7.1 Van earthquake, Turkey, 2011

J. Zahradnik1, E. Sokos2, J. Jansky1, V. Plicka1

1) Charles University in Prague, Czech Republic2) University of Patras, Greece

Mw 7.1 (USGS) October 23, 2011

Our quick report to EMSC 7 days after earthquake.

Part 1 – location by 3 methods

Problems: VMUR a TVAN clipped in S,

other stations - unclear S-onsets

Turkish SM 6503, 4902 and Iranian SM stations

with no absolute time

“P&S”epic. 38.7163 43.4045depth 8.1 km origin time 10 41 21.22ERH 1.7, ERZ 2.0

NLL depth histogram

NLL depth histogram

In contrast to ~ 1 km conventional estimates,hypocenter uncertainty

is ~ 5 km.

Therefore: It should not be used to constrain

the slip models (as many people do…).

How efficient is the location when using just seven nearest SM stations of the

Turkish network?

The answer comes from the

Source Scanning Algorithm

(Kao et al. with our modification). See our POSTER today, Aug. 20

DAP5: P102 Janský et al.

Without 6503

With 6503

LAT(km)

LON (km)

Without 6503

With 6503

Without 6503

With 6503

Without 6503

With 6503

good

bad

The seven nearest SM stations efficiently locate the event by the SSA back-projection; station 6503 is important.

So far, this role of SSA to assess location uncertainty

(including ‘data and modeling errors’) has not been fully recognized.

See our POSTER today, Aug. 20 DAP5: P102 Janský et al.

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SSA can also automatically check the consistency

between the data and the Vp, Vs crustal model.

blue = P-wave stack, pink = S-wave stack

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SSA can also automatically check the consistency

between the data and the Vp, Vs crustal model.

We suggest the correlation between the P- and S-stack to measure quality of the location.

On the other hand – temporal evolution of the SSA (brightness maps) should be

considered with great caution.

Focusing of the brightness should not be misinterpreted as the rupture propagation effect.

Part 2 – centroid moment tensor

epic. distances 330-1290 km periods 100-200 seconds

Deviatoric solution, Variance Reduction = 0.83 a strongly dominant single point source,

strike/dip/rake = 246°, 52°, 75°, DC>90% grid search: 38.689°N, 43.351°E; no depth resolution

Part 3 – major subevent(decreasing period to reveal possible source complexity)

Seven Turkish strong-motion stationsepic. distances ~40 -220 km

periods 10-20 seconds

ISOLA software (Sokos and Zahradnik, 2008) News in our talk tomorrow, Aug. 21ORAL, DAP1+4 O24 14:45-15:00

Six CMG-5TD’s, while6503 was equipped

with an old SigSa smach accelerograph.

But, as shown above, we need 6503…

Excellent data availability from TR-KYH

Instrumental parametersfor Smach (6503) were provided by GeoSig:

10-4

10-2

100

102

104

-220

-200

-180

-160

-140Station 6503 Component (EW)

Frequency (Hz)

Mag

nitu

de (

dB)

10-4

10-2

100

102

104

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-200

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0

100

Frequency (Hz)

Pha

se (

deg)

The deviatoric inversion couldn’t be used at these shorter periods, because it produced a very large (> 50%) spurious non-DC component due to the finite-extent source effect.

Instead – we used the CMT (BB) double-couple mechanism and grid-searched the major subevent: 38.734°N, 43.351°E

Inversion from seven SM’s.Isolines showing

the waveform match:

The deviatoric inversion couldn’t be used at these shorter periods, because it produced a very large (> 50%) spurious non-DC component due to the finite-extent source effect.

Instead – we used the CMT (BB) double-couple mechanism and grid-searched the major subevent: 38.734°N, 43.351°E

Inversion from seven SM’s.Isolines showing

the waveform match:

Major subevent at ~2-5 km west of

hypocenter.

Keeping fixed the DC focal mechanism from the BB solution, and making grid search over depth, we arrived at clear preference of the depths > 10km of the major subevent. (More details, 10-20 km unresolved).

Alternatively, we calculated the DC-constrained solution (by Lagrange multipliers) and found the same position of the

major subevent at 38.734°N, 43.351°E, with strike/dip/rake= 238°, 55°, 63°.

Part 4 – any additional subevents ?

shortest periods further decreased

to 6 seconds

We used a fault plane of the strike/dip/rake angles obtained from the BB data (246°, 52°, 75°), passing through the reference point defined by Lat, Lon coordinates of the major subevent (38.734°N, 43.351°E) and with the depth fixed at 15 km.

Reason? Major subevent and P&S hypocenter represents the H-C consistent solution[Zahradnik et al., SRL 2008].

-200

20

-15-10-5051015-24

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-20

-18

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East-West (km)

Van

North-South (km)

Dep

th

How to constrain the fault plane?

MPS(multiple

point source)

Radii of circlesproportional to moment.

Color refers to rupture time.

Software: New ISOLA.

scale:

Our talk tomorrow, Aug. 21

DAP1+4 O24 14:45-15:00

Twosource contributions

are dominant.

scale:

12

Twosource contributions

are dominant.

Nevertheless, the nearest station 6503

required at least one or two (smaller) subevents.

scale:

34

Note that‘the earliest’

subevent (#3)is close to

epicenter (star).

scale:

34

The nearest station 6503 needs more than two subevents.

Part 5 – stability and uncertainty of the MPS solution

periods > 6 seconds

To check stability we enlarged the fault

and perturbed the MPS solution.

17 18

Perturbation = forcing subevent #1 to be

in a prescribed trial positione.g. 17, 18, 19.

19

17 18 19

Common features:

(i) the solution is relatively concentrated in the central part of the fault

(ii) one of the two largest subevents is always delayed by some 3 s, and is situated more towards SW (in the strike direction)

(iii) the earliest subevent turquoise is small, and it is situated near the largest subevent and near epicenter

(iv) the solutions always contain also a small very late pink subevent, but the position and time of this source contribution is unstable

Analogous solution in case of an artificially damped moments(while increasing number of subevents)

=>

The overall (summed) moment has almost the same spatial distribution.

26.8 km

3.2 km

Comparison with standard slip inversion (Gavin Hayes, USGS NEIC)

Comparison with satellite interferometry by Elisa Trasatti

INGV-Rome.

Comparison ofISOLA (green)

with TSVDslip inversion

(by F. Gallovič)

animace

POSTER today, Aug. 20.RSE1: P007 Ameri et al.

Conclusion

• Significantly poorer station coverage compared to e.g. L’Aquila 2009 results in less certain results.

• We passed from a single source (100-200 s) to multiple-source solution (6-20 s).

• Our solution was constructed independently of the uncertain H, but finally reached H-C consistency.

• Source consisted of at least 3 episodes. • Further work: GPS and high-frequency SM

modeling (see poster of G. Ameri et al.)

Thank you for your attention!

Conclusion

• Significantly poorer station coverage compared to e.g. L’Aquila 2009 results in less certain results.

• We passed from a single source (100-200 s) to multiple-source solution (6-20 s).

• Our solution was constructed independently of the uncertain H, but finally reached H-C consistency.

• Source consisted of at least 3 episodes. • Further work: GPS and high-frequency SM

modeling (see poster of G. Ameri et al.)

Strike Dip Rake238. 55. 63.250. 55. 63.261. 55. 63.

=> Směr šipek určen mechanismem (možná kromě MURA), délka pak rozložením skluzu; u L’Aquily pro stanice nad zlomem složitější!

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Velocity (km/sec)

Dep

th (

km)

Plot of Vp, Vs CLDRmodif1.da

Vp

Vs

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Velocity (km/sec)

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Plot of Vp, Vs

Vp

Vs

Nebezpečné artefakty !

Směr šířenítrhliny

6503

1302Filtr: 0.05-0.06-10.0-12.0

(zrychlení)

Source Model: USGS, from teleseismic data

Simulace silných pohybů pomocí našeho hybridníhointegrálně-kompozitního modelu provedl G. Ameri

M0=5.2e19Nm

Filtr: 0.05-0.06-10-12!

bez kanálu f< 0.1 Hz

s kanálem f< 0.1 Hz

I artificially fixed the position of the first subevent in one of the 49 source grid points. Plotted in the figure are then all four calculated subevents but only if their summary moment was greater than 0.45e20 Nm, and variance reduction was greater than 0.48.

. It can be also shown that (v) the depth of the largest patch trades-off with its size – the deeper the patch, the larger is its moment

LON LAT Depth Source # Time (s) Moment (Nm) Cumul. Moment (Nm) VR

43.35069 38.73398 15.00000 25 33.500 1.810e+019 1.810e+019 0.308

43.26150 38.67075 11.05995 20 37.000 1.133e+019 2.943e+019 0.428

43.46991 38.74686 11.05995 16 30.700 6.304e+018 3.574e+019 0.471

43.28361 38.74006 18.94005 33 45.400 5.505e+018 4.124e+019 0.493