3D P wave velocity structures of crust and their relationship with earthquakes in the Shandong area

Abstract

A high-resolution 3D P-wave velocity structure of the crust in Shandong area was imaged by inverting 13781 arrival times from 1369 local events recorded by Shandong seismic network from 1975 to January 2014. Tomographic results reveal that the P-wave velocity structure of the crust of Shandong area has significant heterougeneities. The blocks on both sides of the Tanlu fault zone show different velocity structures, implying that the Tanlu fault may be a boundary fault. Our results also show that large-scale low velocity anomalies related to the Luxi large-scale detachment structure of Eocene exists below 20 km depth in the Luxi area, which was possibly associated with the westwards subduction of the Pacific plate that made the hot mantle material ascend along the Tanlu fault zone. The distribution of major earthquakes, most of which are of strike-slip type, spatially coincides with the transition zone between the low-velocity zone and high velocity zone, accompanied by the deep fault zone. These low-velocity anomalies may be related to the enriched fluid, which may weaken the lithospheric strength and make the tectonic stresses easier to accumulate there. The boundaries between the low-velocity and high-velocity anomalies may act as an elastic boundary along which tectonic stresses easily accumulate and transfer to the shallow depth of the crust and generate earthquakes.