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Two M5 earthquakes in Corinth Gulf, January 2010

Two M5 earthquakes in Corinth Gulf, January 2010. J. Janský, O. Novotný, J. Zahradník - Prague E. Sokos - Patras. Outline. Records Hypocenter Centroid and moment tensor Finite source Faults ?. Sta tions and records. acceleration. velocity. peak accel. 1.7 m/s 2 Intensity 6 to 7.

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Two M5 earthquakes in Corinth Gulf, January 2010

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  1. Two M5 earthquakes in Corinth Gulf, January 2010 J. Janský, O. Novotný, J. Zahradník - Prague E. Sokos - Patras

  2. Outline • Records • Hypocenter • Centroid and moment tensor • Finite source • Faults ?

  3. Stations and records

  4. acceleration velocity peak accel. 1.7 m/s2 Intensity 6 to 7 displacement the near-field ramp

  5. Pre-shock

  6. Possible signal from hypocenter (P) before signal from asperity (P’). This is not the anti-alias filter effect !

  7. This is the filter effect.

  8. Zooming the first arrival.

  9. S? S? The near-field ramp. Where is S ?

  10. Stations and records – a summary: Clipping of CMG-3T, double P arrival (P, P’?), unclear S onset, a clear near-field ramp at SER (thanks to CMG-5T)…

  11. Location

  12. One event located by many methods.

  13. Grid-search location.

  14. Grid search combined with station-differences; trade off between depth and origin time is eliminated.

  15. One event located by many methods, agencies included. Jan 18

  16. One event located by many methods Jan 22

  17. The two events slightly shifted one to another. Independently supported by a relative location of Jan 22 with respect to Jan 18.

  18. Location - summary: Conjugate gradients, grid search, relative location, all providing a stable epicenter location. Two events close to each other. Depth ~10 km.

  19. Centroid and moment tensor

  20. Distances < 100 km

  21. Specific role of the nearest station. Excluded from inversion. Jan 18 Frequency < 0.2 Hz

  22. Jan 22 strike, dip, rake Jan 18: Plane 1: 108 57 -74 Plane 2: 260 37 -113 Jan 22: Plane 1: 76 38 -108 Plane 2: 279 54 -76

  23. Centroidal depth ~ 3-5 km, independent of crustal models. (Lat 38.4250, Lon 21.9187, model ON)

  24. Uncertainty of the centroid position

  25. Centroid and moment tensor - summary Two normal events, slightly different positions and mechanisms, small centroid depths (~ 4 km).

  26. Fault plane

  27. Jan 18: H-C consistency; fault dipping to South

  28. Jan 18 Yes ! No

  29. Jan 18, Jan 22 Jan 18 ?? Yes ! No

  30. Jan 22: H-C consistency achieved when C shifted by 0.02° to North.

  31. If the H depths are 8 km, both H’s are in the same plane determined by the strike and dip of Jan 22.

  32. Caution: These are the two likely fault planes, not the conjugate nodal planes !

  33. Fault plane - summary Jan 18 fault plane dipping to South, Jan 22 a bit more problematic (a Northward 0.02° shift of C would be needed, but allowed within the uncertainty limits). Relation to surface faults is unclear.

  34. Fault plane – additional data ?

  35. Preliminary location of the sequence (Patras Univ.)

  36. Finite-fault modeling (forward simulation for SER) 25 43 Finite-source effects are evident, but no simple preference can be made.

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