ANALYSIS OF THE MICROSEISMICITY (1996-2007) OF THE SANTA MONICA MOUNTAINS AND ASSOCIATED MALIBU COAST, SANTA MONICA-DUME, AND SANTA MONICA BAY FAULTS

The Santa Monica Mountains, in the western Transverse Ranges, are separated from Los Angeles and offshore Santa Monica sedimentary basins by the E-W, now predominantly left-lateral Raymond-Hollywood-Santa Monica-Dume fault system. The western ~80 km-long stretch of this fault system has been investigated by Sorlien et al (2006) using seismic reflection and earthquake data. Previous investigators proposed thrust slip on a low-angle blind fault beneath the Santa Monica-Dume fault to account for the Santa Monica anticlinorium. The onshore Malibu Coast fault (MCF) and the onshore Santa Monica fault are probably oblique left-reverse faults. The Malibu Coast fault shows evidence of reverse-oblique slip with a left-lateral strike-slip component along north-dipping strands ranging from 30-70 degrees. Though Holocene surface displacements have been officially recognized across only two strands of the MCF zone to date, the MCF is still considered active and capable of producing a magnitude 6.5 to 7.0 earthquake. The microseismicity (1996-2007; M=1-3, 307 events) for the region has been relocated using HYPOINVERSE 2000 and the SCEC/LARSEII crustal velocity structure. The results show seismicity (map view and cross-sections) associated with the Malibu Coast, Santa Monica-Dume, and Santa Monica Bay faults, as well as scattered events in the eastern region of the Santa Monica Mountains. The focal mechanisms show primarily reverse and some left-lateral slip faulting.