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Fast determination of earthquake source parameters from strong motion records:

Fast determination of earthquake source parameters from strong motion records: Mw, focal mechanism, slip distribution B. Delouis, J. Charlety, and M. Vallée Géosciences Azur CNRS/IRD Université de Nice – Sophia Antipolis. EGU General Assembly 13-18 April 2008 Vienna Austria.

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Fast determination of earthquake source parameters from strong motion records:

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  1. Fast determination of earthquake source parameters from strong motion records: Mw, focal mechanism, slip distribution B. Delouis, J. Charlety, and M. Vallée Géosciences Azur CNRS/IRD Université de Nice – Sophia Antipolis EGU General Assembly 13-18 April 2008 Vienna Austria

  2. Fast determination of earthquake source parameters fromstrong motion records: Mw, focal mechanism, slip distribution B. Delouis, J. Charlety, and M. Vallée Géosciences Azur CNRS/IRD Université de Nice – Sophia Antipolis

  3. Overview and objectives: Step 2 Step 1 Step 3 All this using near source records

  4. Earthquake detection and localisation Early warning "Early P-wave magnitude" A few seconds Step 1 Moment magnitude Mw 2 minutes Rapid source parameters Step 2 15 minutes Focal mechanism Step 3 40 minutes Slip distribution Where are we in the time scale of Seismic Warning ? Earthquake origin time Global CMT solutions: > 1 hour TIME

  5. Step 1: Fast Moment Magnitude Mw

  6. 4 p ra3 r W0 M0 = ——————— Rp cor_free_surf Classical way to determine Mw from the far-field body waves Far field (distance >> rupture dimension) W0 = spectral level at low frequency Valid for separated far-field waves (P and S) only. This simple relation cannot be used when P, S, and near-field waves are intermixed as it is the case near the source for large earthquakes. (Kanamori 1977)

  7. A new approach: Using synthetic displacement spectra generated for extended sources in the near-field domain

  8. virtual stations

  9. Validation with 22 earthquakes worldwide with Mw ranging from 3.9 to 7.7 Using a time window of 80 sec after origin time

  10. Step 2: Fast Focal Mechanism using a line source model

  11. If magnitude < 5.5  point source Parameters to be inverted for: Fault strike, dip, rake and … If magnitude > 5.5  finite line source 5.5 < M < 6 6 < M < 7 7 < M < 7.5 M > 7.5

  12. N 100 km Example 1: 1999 Chi-Chi earthquake Mw 7.6

  13. 100 km Example 2: 1999 Izmit Mw 7.6

  14. 50 km Example 3: 2000 Tottori earthquake Mw 6.7 N The method has been validated for 19 earthquakes worldwide of moment magnitude 3.6 to 8.0

  15. Step 3: Fast Slip Inversion (under development and validation)

  16. : hypocenter

  17. 1999 Chi-Chi earthquake Mw 7.6 Test of standardized slip inversion NNE East-dipping rupture plane SSW : hypocenter NNE SSW

  18. Conclusions • It is possible to determine a moment magnitude Mw from near source stations at distance < 100 km with an acceptable degree of accuracy (+/- 0.2), over a very wide range of magnitude (4 to 8). Expected time scale: < 2 min after origin time • The focal mechanism can be retrieved in the same conditions using a simple line source model. Expected time scale: < 15 min after origin time • A fast and automated slip inversion is feasible (presently under development and validation). Expected time scale: < 45 min after origin time

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