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EMSC

Cythera M6.7 earthquake (January 8, 2006) in southern Aegean: uneasy retrieval of the upward rupture propagation J. Zahradnik, J. Jansky, V. Plicka, E. Sokos Charles University in Prague University of Patras. EMSC. Diverse centroid position Unclear aftershock pattern

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EMSC

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  1. Cythera M6.7 earthquake (January 8, 2006) in southern Aegean: uneasy retrieval of the upward rupture propagationJ. Zahradnik, J. Jansky, V. Plicka, E. Sokos Charles University in Prague University of Patras

  2. EMSC • Diverse centroid • position • Unclear aftershock • pattern • Unclear fault • Low DC%: • ETH 60%, Mednet 56%

  3. Inconsistent hypocenter and centroid moment solution nodal planes, and centroid in the middle

  4. Teleseismic recordsKikuchi-Kanamori method • pP: depth • P: complexity P pP

  5. Bottom trace = synthetics (K & K) simple event and complex event

  6. Regional records and EGF method apparent source time functions prove complexity ... Neighborhood Algorithm provides two slip patches (similar to M. Vallée) plane 2 strike ~70° plane 1 strike ~200°

  7. Lower misfit identifies the fault plane: strike ~70°

  8. Relocation • 30 teleseismic stations, pP-P: depth 90 km • 21 regional stations (Greece + Italy), P and S • Wadati diagram: Vp/Vs=1.75 • Optimization of RMS: Vp/Vs=1.75 • Relocation of regional data with first approximation of depth = 90 km and Vp/Vs=1.75 with various azimuthal and epic.distance weighting schemes

  9. Free depth: This is uncertainty of mainshock location, not the aftershocks !

  10. First approximation of depth 90 km:

  11. Optimized Vp/Vs ratio:

  12. hypo1 EMSC this study We relocated hypocenter 15 km South, 10 km East and 25 km below EMSC.

  13. ISOLA code (Fortran & Matlab) multiple point-source moment tensors Full waveform modeling of regional records Free on web:

  14. Iterative deconvolution (Kikuchi and Kanamori) modified for regional recordsMoment tensor (deviatoric, or DC-constrained)at each trial space-time position by minimization of the L2 waveform misfit(least squares)Optimum space-time positionof subevents by maximization of the waveform correlation (grid search)

  15. Free BB waveformdata(Internet) Our LTK station soon on Orfeus, too.

  16. Waveform modeling for f<0.1 Hz enables the source study

  17. Hierarchic grid search of centroid f < 0.1 Hz EMSC EMSC epic. is just the coordinate origin search 1  search 2, etc.

  18. Accurate centroid location needed for usable DC% search 1 search 2

  19. Getting more accurate centroid makes DC% to converge search 2 search 3… DC% 10-30 only !

  20. We found centroid25 km East of EMSC epicenterand the DC% has convergedto 10-30%.Does it imply that the source is actually strongly non-DC ?Not !

  21. DC-constrained solution is an equivalent model deviatoric DC-constrained M EMSC and Mednet M Note different optimal source position.

  22. Can we better justify our centroid position and MT ?Remember the inconsistency for Mednet centroid and EMSC hypocenter:

  23. Our CMT is fully consistent with our relocation. Far from being trivial!5 … and it identifies the fault plane as the “red” nodal plane, strike ~ 80°

  24. The EMSC hypocenter is also in the fault plane o5

  25. The BB first-motion polarities are consistent with the CMT solutiono5 Red: this study Black: others

  26. Where’s complexity found in EGF analysis and teleseismic modeling ? For f < 0.1 Hz, in addition to stable subevent 1 (1.1e19 Nm) the waveforms clearly indicate subevent 2, 6-sec later, comparable size ! (1.1e19 Nm) Sub 1 ? Sub 2 ? M Solution for sub2 is not unique.

  27. Seeking sub 2 in the fault plane of sub 1: DC-constrainedpo5 X 1 depth 60 km 2 X depth 85 km depth 72 km X…EMSC X…this study

  28. A double-event interpretation: • Subevent 1: 1.10e19 Nm strike, dip, rake: (84, 64, 121)=(209 40 43) • Subevent 2(6 sec later): 0.87e19 Nm strike, dip, rake: (61, 86, 52)=(326, 38, 174) Depths Sub 1: 60 km Sub 2: 76 km Hyp.: 85 km EMSC 1 2 this study

  29. Possible explanation of the apparently large non-DC: Summing up MT of these two 100% DC events provides a non-DC solution strike, dip, rake: (82, 70, 94) 1.6e19 Nm, DC%=57 near to long-period Mednet CMT strike, dip, rake: (81, 67, 139) 1.4e19 Nm, DC%=56 But Mednet centroid is too far… 1 2 M

  30. Can we identify fault plane of subevent 2 ? + 1 x 2

  31. Can we identify fault plane of subevent 2 ? 5 1 1 2 2 strike 61° strike 326° Nodal plane with strike 326° passes through the hypoc. !

  32. Nodal plane with strike 326° passes through the hypoc. ! hypo5

  33. hypo5 1 2 2 1 common hypoc. Depths Sub 1: 60 km Sub 2: 76 km Hyp.: 85 km Hypothesis: both patches (on different fault planes) nucleated close to the same point, and ruptured upward, sub 2 being delayed with respect to sub 1.

  34. Another possibility:fixed DC focal mechanism (that of sub 1).It moves sub 2 close to sub 1. X 1 2 Depth 60 km depth 69 km X depth 72 km X…EMSC X…this study

  35. Another possibility:fixed DC focal mechanism (that of sub 1)moves sub 2 close to sub 1 1 2 now we do not need the left segment depth 60 km depth 69 km … but how to explain low DC % and why the 6-sec delay ?

  36. strike, dip, rake: 84° 64°, 121° (for both) Interpretation I: Fixed mechanism Varred= 52% 69 and 60 km x hypocenter depth 85 km (this study) 84°, 64°, 121° Interpretation II: DC-constrained Varred=64% !! 329°, 36°, 179° 60 km x 72 km 85 km

  37. Methodical lesson and Cythera model • Relocation and CMT inversion in same model enabled identification of the fault plane (strike ~80°) of the main patch. • Hierarchic space-time grid search lead to convergence of the DC% to a low value. • 100% DC-constrained solution provided a double-event model and explained the low DC% as only apparent non-DC. • Rupture started at depth 85 km. Most stable slip patch was centered 35 km apart, at depth 60 km. • Second large patch was delayed by 6 sec. Position and mechanism not unique. Possibly on a different fault plane. http://geo.mff.cuni.cz

  38. The most important essence is visions and dreams http://geo.mff.cuni.cz

  39. „Blind“ experiment on slip inversion from synthetic data (EC projekt SPICE) Data = synthetics for a „secret“ slip distribution

  40. New BB satellite network Patras Univ. green= Trillium and CMG = status May 21

  41. ITSAK-GR 2006-2009 starts right these days = a new EC Marie Curie RTN accelerographs near Cythera available ! Ch. Papaioannou

  42. The fault plane is needed for correct identification of the slip patches apparent source time functions from EGF method ... and slip patches by NA algorithm

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