鸟取M_(JMA)7.3级地震震源区地震层析成像研究

Seismic Tomographic Imaging for the Source Area of the Tottori Earthquake

采用2000年日本鸟取MJMA7.3级地震的907个余震及其地方震的24 756个P波和22 547个S波到时,确定鸟取地震震源区的P波、S波和泊松比的三维结构.在震源区地震波速变化幅度达4%,泊松比变化幅度达9%.在11 km深度发现高波速和低泊松比异常,表明这一部位为刚性的粗糙断层面,形成断裂带的锁定结构,它的破裂产生鸟取地震的主震.低波速和高泊松比异常在震源区之下的地壳中出现,这与菲律宾板块俯冲带的脱水过程和岩浆活动有关,导致Daisen弧后火山的形成.流体运动和岩浆活动,对鸟取地震的成核和破裂过程有重大的影响.

Investigating material properties in the source areas of large earthquakes is very important for understanding the seismogenic behavior. Using 24 756 P wave and 22 547 S wave arrival times from 907 aftershocks and other local earthquakes, the authors determined the 3-D P and S wave velocity and Poisson＇s ratio structures in the Tottori epicentral area. Significant variations of up to 4 % for seismic velocity and 9 % for Poisson＇s ratio are revealed in the source area. High velocity and low Poisson＇s ratio anoma- lies are detected down to 11 km depth, which are interpreted as a strong and brittle asperity in the Tottori fault zone that ruptured during the mainshock. Low velocity and high Poisson＇s ratio anomalies that detect- ed in the lower crust are considered to associate with the dehydration process of the subducting Philippine Sea slab, leading to the formation of the arc volcano, Mt. Daisen. The fluid transportation and magmatic activity have great influence to the nucleation and rupture process of the Tottori earthquake.