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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 J. Janský, O. Novotný, J. Zahradník - Prague E. Sokos - Patras
Outline • Records • Hypocenter • Centroid and moment tensor • Finite source • Faults ?
acceleration velocity peak accel. 1.7 m/s2 Intensity 6 to 7 displacement the near-field ramp
Possible signal from hypocenter (P) before signal from asperity (P’). This is not the anti-alias filter effect !
This is the filter effect.
S? S? The near-field ramp. Where is S ?
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)…
Grid search combined with station-differences; trade off between depth and origin time is eliminated.
One event located by many methods, agencies included. Jan 18
The two events slightly shifted one to another. Independently supported by a relative location of Jan 22 with respect to Jan 18.
Location - summary: Conjugate gradients, grid search, relative location, all providing a stable epicenter location. Two events close to each other. Depth ~10 km.
Specific role of the nearest station. Excluded from inversion. Jan 18 Frequency < 0.2 Hz
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
Centroidal depth ~ 3-5 km, independent of crustal models. (Lat 38.4250, Lon 21.9187, model ON)
Uncertainty of the centroid position
Centroid and moment tensor - summary Two normal events, slightly different positions and mechanisms, small centroid depths (~ 4 km).
Jan 18 Yes ! No
Jan 18, Jan 22 Jan 18 ?? Yes ! No
Jan 22: H-C consistency achieved when C shifted by 0.02° to North.
If the H depths are 8 km, both H’s are in the same plane determined by the strike and dip of Jan 22.
Caution: These are the two likely fault planes, not the conjugate nodal planes !
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.
Finite-fault modeling (forward simulation for SER) 25 43 Finite-source effects are evident, but no simple preference can be made.