Uncertainty of location and multiple-point source model of M 7.1 Van earthquake, Turkey, 2011 J. Zahradnik 1, E. Sokos 2, J. Jansky 1, V. Plicka 1 1) Charles University in Prague, Czech Republic 2) 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 depth 8.1 km origin time ERH 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.

SSA can also automatically check the consistency between the data and the Vp, Vs crustal model. blue = P-wave stack, pink = S-wave stack

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 km periods seconds

Deviatoric solution, Variance Reduction = 0.83 a strongly dominant single point source, strike/dip/rake = 246°, 52°, 75°, DC>90% grid search: °N, °E; no depth resolution

Part 3 – major subevent (decreasing period to reveal possible source complexity) Seven Turkish strong-motion stations epic. distances ~ km periods seconds ISOLA software (Sokos and Zahradnik, 2008) News in our talk tomorrow, Aug. 21 ORAL, DAP1+4 O24 14:45-15:00

Six CMG-5TD’s, while 6503 was equipped with an old SigSa smach accelerograph. But, as shown above, we need 6503… Excellent data availability from TR-KYH

Instrumental parameters for Smach (6503) were provided by GeoSig:

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: °N, °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: °N, °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, km unresolved).

Alternatively, we calculated the DC-constrained solution (by Lagrange multipliers) and found the same position of the major subevent at °N, °E, with strike/dip/rake= 238°, 55°, 63°.

Note asymmetry of the correlation isolines due to limited azimuthal coverage.

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, °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]. How to constrain the fault plane?

MPS (multiple point source) Radii of circles proportional to moment. Color refers to rupture time. Software: New ISOLA. scale: Our talk tomorrow, Aug. 21 DAP1+4 O24 14:45-15:00

Two source contributions are dominant. scale: 1 2

Two source contributions are dominant. Nevertheless, the nearest station 6503 required at least one or two (smaller) subevents. scale: 3 4

Note that ‘the earliest’ subevent (#3) is close to epicenter (star). scale: 3 4

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 Perturbation = forcing subevent #1 to be in a prescribed trial position e.g. 17, 18,

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 km 3.2 km

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

Comparison with satellite interferometry by Elisa Trasatti INGV-Rome.

Comparison of ISOLA (green) with TSVD slip 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 ( 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 ( 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 Rake => Směr šipek určen mechanismem (možná kromě MURA), délka pak rozložením skluzu; u L’Aquily pro stanice nad zlomem složitější!

Nebezpečné artefakty !

Směr šíření trhliny Filtr: (zrychlení)

Source Model: USGS, from teleseismic data Simulace silných pohybů pomocí našeho hybridního integrálně-kompozitního modelu provedl G. Ameri M0=5.2e19Nm

Filtr: !

bez kanálu f< 0.1 Hz

s kanálem f< 0.1 Hz

UNCERTAINTY OF THE LOCATION AND MULTIPLE-POINT SOURCE MODEL OF M 7.1 VAN EARTHQUAKE, TURKEY, 2011 J. Zahradnik 1, E. Sokos 2, J. Jansky 1, V. Plicka 1 1) Charles University in Prague, Czech Republic 2) University of Patras, Greece

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 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 e e e e e e e e

Do we have any method providing the uncertainty estimate including ‘data errors’ and ‘modeling (crustal structure) errors’? Yes, we believe that such a method is the Source Scanning Algorithm (Kao et al. with our modification) See our POSTER !