1. Main shock (27/02/2010)

2. "Aftershock" 11/03/2010

1. Fast teleseismic body-wave source inversion of the main shock
(SCARDEC method)

Martin Vallée (Géoazur, IRD, Nice, France, vallee@geoazur.unice.fr)
Jean Charléty (Géoazur, CNRS, Nice, France, charlety@geoazur.unice.fr)
Collaboration with A. Ferreira (UEA, Norwich,UK) and LDG/CEA (Paris, France)

 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 -0.17Hz).

 Remarks

 Giant subduction earthquake (Mw=8.7-8.8 ; Figure 1). The thrust focal mechanism and the depth (between 21km and 39km) confirms a major interplate event. Temporally, the earthquake is dominated by a relatively simple moment release, lasting about 2 minutes (Figure 2).

Directivity effects can be seen in the Relative Source Time Functions presented in Figure 2 (shorter durations in the Northern azimuths, longer durations in the Southern azimuths). It indicates that, unlike most subduction earthquakes known along the South-American margin, this earthquake has a significative part of its rupture propagation from South to North.

Figures

Figure 1 : Source parameters, uncertainties and agreement with teleseismic data. (Top left) Optimal values of moment magnitude, depth and focal mechanism. (Bottom left) Uncertainty analysis used to determine the acceptable values of dip, depth and magnitude (see values in the bottom). (Right) Agreement between data (black) and synthetics (red), both for compressive (i.e. P, PcP, PP) waves and transverse (i.e. S, ScS) waves (frequency band : 0.005-0.03Hz). Name of the station, azimuth, distance and maximum amplitude (in microns) are shown for each signal.

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

2. Aftershock : 11/03/2010, 14h39 :

(lat,lon =-34.18,-71.9 ; Mw= 6.9) 

 Comments : Impulsive shallow normal earthquake. Depth is found not deeper than 20km.