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CRYSTALLINE BASEMENT STRUCTURE OF CHANGBAISHAN TIANCHI VOLCANIC AREA

The crystalline basement velocity structure of Changbaishan Tianchi volcanic area is established by using Three Dimensional Finite Difference method and Pg data from four wide angle reflection/refraction profiles and one three dimensional array which was deployed in Changbaishan Mountain area. This paper presents the characteristics of the velocity structure of crystalline basement and the interface with 5.9～6.0km/s P wave velocity in the crystalline basement. Inversion results reveal that the velocity of surface layer in the southern part is higher than that in the northern part of the studied area. In general, the depth of crystalline basement of the studied area is within the range of 2.0～3.0km, with the deepest of about 4.0km and the shallowest of about 1 5km near Songjiang. There are two low velocity areas in this region, one is beneath the Protection Station of Tianchi volcano, and the other is located beneath Erdaobaihe and Chixi Protection Station. In these two areas the depths of crystalline basement are about 4.0km. We found that the intense lateral variation of velocity and depth of crystalline basement in the seismic profile coincides well with the location of fault. Therefore, it is suggested that the intense lateral variation of velocity and the abrupt change of the depths of crystalline basement can be taken as an indication of the occurrence of fault.