New moment magnitude scale, evidence of stress drop magnitude scaling and stochastic ground motion model for the French West Indies

Abstract

International audienceIn this study we analyse records from the 'Les Saintes' seismic sequence following the Mw= 6.3 earthquake of 2004 November 11, which occurred close to Guadeloupe (French West Indies). 485 earthquakes with magnitudes from 2 to 6, recorded at distances between 5 and 150 km are used. S-waves Fourier spectra are analysed to simultaneously determine source, path and site terms. The results show that the duration magnitude routinely estimated for the events that occurred in the region underestimate moment magnitude by 0.5 magnitude units over the whole magnitude range. From the inverted seismic moments and corner frequencies, we compute Brune's stress drops. We show that stress drops increase with increasing magnitude. The same pattern is observed on apparent stresses (i.e. the seismic energy-to-moment ratio). However, the rate of increase diminishes at high magnitudes, which is consistent with a constant stress drop model for large events. Using the results of the inversions, we perform ground motion simulations for the entire data set using the SMSIM stochastic simulation tool. The results show that a good fit (σ= 0.25) with observed data is achieved when the source is properly described by its moment magnitude and stress drop, and when site effects are taken into account. Although the magnitude-dependent stress drop model is giving better results than the constant stress drop model, the interevent variability remains high, which could suggest that stress drop depends on other parameters such as the depth of the hypocentre. In any case, the overall variability is of the same order of magnitude as usually observed in empirical ground motion prediction equations

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

“…(2011), Drouet et al (2011), and the observation shown in our study. The station classification is done according to the angle between the strike of the main-shock fault orientation, as given by Feuillet et al (2011), and the source-tostation direction.…”

“…The recent study of Drouet et al (2011) provided updated regional attenuation relationships and amplification factors of the accelerometric stations in this area. Through this new information, we have been able to analyze the corrected source spectra of the Les Saintes earthquake sequence and to evaluate how the source affects control of the observed spectra.…”

“…Red stations, <30°(western Guadeloupe Island); green stations, from 30°to 75°(eastern Guadeloupe Island); yellow stations, azimuth perpendicular to the strike; blue stations, located in the anti-strike direction (Martinique Island). Modified from Drouet et al (2011) andFeuillet et al (2011) In the log domain, Eq.…”

“…The spectra were smoothed using the Konno and Ohmachi (1998) smoothing procedure, following Drouet et al (2011). Then, we applied the correction described in Eq.…”

Spectral models for ground motion prediction in the L'Aquila region (central Italy): evidence for stress-drop dependence on magnitude and depth

“…(1) can be performed either following a parametric approach, where the unknown functions related to source and propagation are expressed in terms of standard models (e.g. Kawase 2006;Tsuda et al 2006Tsuda et al , 2010Salazar et al 2007;Drouet et al 2008Drouet et al , 2011, or following a non-parametric inversion scheme (e.g. Castro et al 1990;Parolai et al 2000Parolai et al , 2004Oth et al 2008Oth et al , 2009.…”