The Velocity Structure And Structural Feature Of Crust In The Northern Hainan Region

Seismic method has its unique advantages to get the characteristics of the depthstructure, it has a wide range of applications on the research of deep tectonic setting,Seismogenic dynamics, territorial resources exploration, and so on,the artificial seismicsounding method is the most effective method for get the fine structure of the earth crustand mantle.The northern Hainan has a complex geological structure and active seismicactivities.In this paper, the comparative analysis of artificial seismic sounding profilewhich is the length of200km in northern Hainan is made, in view of the differentcharacteristics of seismic phase, analyzes the datas with the method of basal refractionwave travel time inversion,the reflected wave inversion, one-dimensional travel timeinversion, two-dimensional dynamic ray tracing and so on, to get the structural feature ofthe earth crust and the upper mantle in the north of Hainan. The result shows that the earthcrust of this area is divided into the upper crust, the middle crust and the lower crust, thethickness of the upper crust is11.5-14.5km, the thickness of the middle crust is5.6-8.5km,the thickness of the lower crust is6.0-8.2km. The form fluctuation of C1interface arerelatively obvious, the range of variation of depth is11.5-14.5km, the depth of the C2interface is18.0-21.7km, the depth of Moho interface is26.0-29.5km, the velocity of thetop of upper mantle is8.00-8.15km/s, the velocity increases with the increase of the depth,it’s8.38-8.56km/s when the depth is40.0km.The results of crust-mantle structure show that the middle and lower crust have lowvelocity region which is north-west trend, it moves northward in the upper mantle,concentrated at the north of Qiongbei volcanic zone and Qiongzhou Strait, the middle andlower crust in volcanic zone still have comparatively active thermal motion, maybe thethermal materials come from the northern Qiongzhou strait. Therefore, it can infer that the magmas which once act on detection area should be derived from the mantle of northernseismic survey line. At the same time, understanding the crust-mantle structural feature andgeodynamic processes in the Leiqiong area is significant to the Leiqiong area (especially inHaikou and its neighboring region).