High-frequency directivity effects: Evidence from analysis of the Les Saintes records

Abstract

The main-shock (Mw, 6.3) and the aftershocks of the 'Les Saintes' earthquake sequence (French Indies) were analyzed to quantify high-frequency directivity effects. A correction method was applied to isolate source spectra within a large frequency range (0.5 to 25 Hz). Most of the aftershocks source spectra are fully consistent with a Brune spectrum point-source shape and do not show any azimuthal dependence. The main-shock (Mw, 6.3) and the two largest aftershocks (Mw, 5.8, 5.3) show, however, a clear azimuthal dependence that indicates significant directivity effect. The discrepancy of the radiated spectral energy and the change in the corner frequencies introduced by directivity effects show that such an effect is significant at high frequency (from 1 to 25 Hz). Our data suggest that the amplitudes in the main-shock Fourier spectrum at directive sites are around a factor of 2.5 higher with respect to anti-directive sites. © 2014 The Author(s).