Diapositive 1

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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 Mw, focal
mechanism, slip distribution B. Delouis, J.
Charlety, and M. Vallée Géosciences Azur CNRS/IRD
Université de Nice Sophia Antipolis
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Overview and objectives
Step 2
Step 1
Step 3
All this using near source records
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Where are we in the time scale of Seismic Warning
?
Earthquake origin time
Global CMT solutions gt 1 hour
TIME
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Step 1 Fast Moment Magnitude Mw
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Classical way to determine Mw from the far-field
body waves
Far field (distance gtgt 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)
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A new approach Using synthetic displacement
spectra generated for extended sources in the
near-field domain
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Validation with 22 earthquakes worldwide with Mw
ranging from 3.9 to 7.7
Using a time window of 80 sec after origin time
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Step 2 Fast Focal Mechanism using a line source
model
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If magnitude lt 5.5 ? point source
Parameters to be inverted for Fault strike, dip,
rake and
If magnitude gt 5.5 ? finite line source
5.5 lt M lt 6
6 lt M lt 7
7 lt M lt 7.5
M gt 7.5
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Example 1 1999 Chi-Chi earthquake Mw 7.6
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Example 2 1999 Izmit Mw 7.6
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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
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Step 3 Fast Slip Inversion
(under development and validation)
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hypocenter
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1999 Chi-Chi earthquake Mw 7.6
Test of standardized slip inversion
East-dipping rupture plane
NNE
SSW
hypocenter
NNE
SSW
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Conclusions

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