HR: 1330h
AN: S42E-0212    [PDF]
TI: Source Characteristics of the Loreto, Mexico Earthquake of March 12, 2003 (Mw=6.4) that occurred in a transform fault in the Gulf of California.
AU: * Lopez-Pineda, L
EM: leolopez@cicese.mx
AF: Centro de Investigaci¢n Cient¡fica y Educaci¢n Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Rebollar, C J
EM: rebollar@cicese.mx
AF: Centro de Investigaci¢n Cient¡fica y Educaci¢n Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Perez-Vertti, A
EM: aperez@cices.mx
AF: Centro de Investigaci¢n Cient¡fica y Educaci¢n Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Mendoza, J A
EM: antonio@cicese.mx
AF: Centro de Investigaci¢n Cient¡fica y Educaci¢n Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AB: We analyzed the Loreto earthquake of March 12, 2003 (Mw=6.4) that occurred in the transform fault that joins the Guaymas and Carmen Basins in the middle of the Gulf of California, Mexico. This event was recorded by two networks of autonomous continuous recording broad-band seismographs (the NARS-Baja network of Utrecht University and the RESBAN network of CICESE). These seismic networks are located along the Baja California Peninsula, and the Sonora and Sinaloa provinces of Mexico. The main event was located at $26.5\deg$N and $111.05\deg$W at a depth of $5.0\pm 2$ km. One foreshock and 40 aftershocks were located southeast of the main shock over a fault of approximately 60 km of length. A statistical analysis of the aftershock sequence gives a b value of 0.68. Focal depth and fault geometry were estimated from body-wave form modeling of S-waves. Synthetic seismograms were calculated using the computer codes developed by Herrmann (1987). We used a triangular source time function of 6 seconds, as inferred from the record at station NE77, located 72 km from the epicenter. The best match between syntetics and recorde S-Waves were obtained with a fault geometry given by a strike of $117\deg \pm 4\deg$, a dip of $79\deg \pm 2\deg$ and a slip of $168\deg \pm 2\deg$. This fault geometry agrees with the solution reported by NEIC. S-wave spectra (uncorrected for seismic attenuation) at station NE77, shows an omega-square decay at high frequencies. We calculated, from the spectral analysis of S-waves, a seismic moment of $4.6x10^{18}$ N-m, a source radius of 9.7 km and a static stress drop that may vary in the range from 13 to 23 bars, assuming a circular source model.
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2003 Fall Meeting