Sismicité sur la côte Ligure
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Séisme Sud-Sumatra
30 septembre 2009 - Magnitude 7.5

jeudi 1er octobre 2009 par Martin Vallée

Fast teleseismic body-wave source inversion

Martin Vallée (Géoazur, IRD, Nice, France, vallee@geoazur.unice.fr)
Jean Charléty (Géoazur, CNRS, Nice, France, charlety@geoazur.unice.fr)
Collaboration with LDG/CEA

 
Method

 We have deconvolved the compressive (P, PcP, PP) and transverse (SH,ScS) teleseismic waves recorded by FDSN-Geoscope stations to simultaneously retrieve the focal mechanism, moment magnitude and source time functions (Frequency band : 0.005Hz -0.33Hz).

 Remarks

 Intermediate-depth earthquake (depth close to 80km), with strike orthogonal to the Sumatra trench. Complex stress regime inside the slab should be responsible for this event.

. Impulsive rupture, with a main moment release lasting about 12s.

 

Figures

Figure 1 : Source parameters, uncertainties and RSTFs. (Top left) Optimal values of moment magnitude, depth and focal mechanism. (Bottom left) Uncertainty analysis : misfit and moment magnitude changes as a function of dip and depth variations around their optimal values. Optimal dip and depth are indicated by the white diamond (the best misfit value is also shown). The thick line is the iso-misfit contour (noted C1) joining points with misfit 10% larger than the best value. The four thin lines are the iso-misfit contours joining points with misfit 25%, 50%, 75% and 100% larger than the best value. Moment magnitude associated with each (dip-depth) couple is shown with the colorscale. Acceptable values of dip, depth and magnitude are those which are inside the C1 contour. (Right) Relative source time functions (RSTFs) for compressive and transverse waves. The values between parentheses are the absolute maxima (in N.m/s) of the RSTFs, respectively for compressive and transverse waves. For each RSTF, the name of the station, its azimuth and epicentral distance are shown.

 

 

 Figure 2 : High frequency RSTFs, in the time and frequency domains. (Top left) Optimal values of moment magnitude, depth and focal mechanism. (Bottom left) Spectrum of the high frequency RSTFs. The classical omega-2 slope is shown in the left part of the figure. (Right) High frequency RSTFs, in the time domain, for compressive waves. For each RSTF, the name of the station, its azimuth and epicentral distance are shown.