Source parameters of the July 30, 2006 (Mw 5.5) Gulf of California earthquake and a comparison with other moderate earthquakes in the region

Abstract

On July 30, 2006 at 01:20:52.28 (UTC) an earthquake of Mw 5.5, occurred in central Gulf of California (GoC), 226 km from Topolobampo and north-west of the transform fault between Guaymas and El Carmen basins.
The earthquake was recorded on six broadband stations of the NARS-Baja seismic network (NE75, NE76, NE77, NE79, NE81 and NE82), and one broadband station of the RESBAN seismic network (TOPB). All stations were located within of epicentral distances of 70 to 220 km. From spectral analysis of SH-waveforms, the source dimensions, seismic moment, stress drop, source time and average displacement of this earthquake were obtained. The fault mechanism estimated by inversion of the seismic moment tensor yields a right lateral strike slip fault mechanism in agreement well with regional tectonics. Principal axes of the stress field (average azimuth 160º) matches the regional trend of the stress field of GoC (about 168º). We propose that the great majority of moderate magnitude earthquakes in this region, have right lateral strike-slip mechanism with principal stress oriented NW-SE. From the seismic history, the motion between plates can be described; moreover, plate motions along the Northwest-Southeast plate boundary between the Pacific and the North-America plates agree well with the regional seismic activity as obtained from the principal stress axes of moderate earthquakes in the region.