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地震精定位及其震源机制可以说明断裂的大陆边缘形变的分布和模式。加利福尼亚湾(GoC)内的太平洋—北美(Pa-NA)板块边界由于北部的大陆扩张到南部转变成海底扩张而提供了研究断裂演化和运动学的极好机会。从2005年10月至2006年10月,作为科特斯海海底台阵(SCOOBA)试验的一部分,在加利福尼亚湾布设的8个四分量海底地震计的台阵记录了地震活动。通过将这次记录数据与自动记录地震(NARS)-Baja台阵陆上台网的观测资料相结合,我们主要沿勾画出板块边界的北西—南东走向的转换断层观测并定位了约700个地震(MW2.2~6.6)。对于在长周期(10~20s)频带具有高信噪比的36个地震事件(MW3.5~6.6),我们通过区域地震波形反演确定了偏矩张量和有关的双力偶震源机制。很多震源机制与沿太平洋—北美转换断层系的右旋走滑断层作用一致,说明这些转换断层主要调节着该海湾内的地震形变。另外,我们在下加利福尼亚上沿右旋北西—南东走向的拉斯比沃拉斯—埃尔阿苏夫雷断层捕捉到可能与该半岛内正在进行的地热活动和火山形变有关的地震群。高分辨率的地震定位与震源机制相结合,提高了我们对加利福尼亚湾南部更大扩张区内地震形变分布的了解。
The precise location of the earthquake and its source mechanism can explain the distribution and pattern of the continental margin deformation at fault. The Pacific-North American (Pa-NA) plate boundaries within the GoC provide an excellent opportunity to study the evolution and kinematics of faults due to the expansion of the northern mainland to the southern transition to a seabed expansion. From October 2005 to October 2006, the array of eight four-component seabed seismometers deployed in the Gulf of California recorded seismicity as part of the Cotez Sea SCOOBA experiment. By combining this recorded data with observations from the NARS-Baja Terrestrial Network, we trace and locate about 700 earthquakes along the Northwest-South Eastward transitional fault line that delineates the plate boundaries (MW 2.2 ~ 6.6). For the 36 seismic events (MW 3.5 ~ 6.6) with high signal-to-noise ratio in the long-period (10 ~ 20s) band, we determined the moment tensor and the related dual-dipole source mechanism by regional seismic waveform inversion. Many focal mechanisms are consistent with the dextral strike-slip faults along the Pacific-North American transformational fault system, indicating that these transformation faults mainly regulate the seismic deformation in this bay. In addition, we trace a north-west-southbound Laspeverlaas-El-Assur fault along Baja California to capture seismic groups that may be associated with ongoing geothermal activity and volcanic deformation in the peninsula. The combination of high-resolution seismic location and focal mechanisms increases our understanding of the seismic deformation distribution over a larger expansion in the southern Gulf of California.