Study On The Temporal And Spatial Distribution Characteristics Of Gravity Field In The Strong Earthquake Region By Using Satellite Gravity Data

Satellite gravity measurement is a new effective method to measure gravity anomalyand temporal gravity variation in earthquake area, volcano area and tsunami area and hasbeen received extensive attention. The study of the gravity field distributioncharacteristics and gravity variation in the strong earthquake region can help us tocomprehend how and why the earthquake happens and the mechanism of the earthquake.The main contents of the dissertation are as follows:(1) The analytic expressions of the gravity variation caused by the point dislocationmodel (vertical tensile dislocation、horizontal tensile dislocation、vertical strike-slipdislocation and vertical dip-slip dislocation) in x and y direction are obtained for the firsttime. The simulated results show that gravity variation graphs in x and y direction aremore complex than the graph in the vertical direction. What’s more, the gravity variationof the vertical strike-slip dislocation in x and y direction present positive and negativealternate distribution in six quadrants. The gravity variation in x direction of the verticaldip-slip dislocation present positive, negative and positive distribution(2) The analytic expressions of gravity gradient variation caused by the pointdislocation in six directions （Txx,Tyy,Tzz,Txy,Txz,Tyz）are acquired for the first time. Thesimulated results show that the gravity gradient variation of the horizontal tensiledislocation in Txxdirection, the vertical dip-slip dislocation in Txzdirection and thevertical tensile dislocation in Tzzdirection all present positive, negative and positivedistribution. While the gravity gradient variation of the vertical strike-slip dislocation inTxydirection and the vertical tensile dislocation in Tyydirection present positive andnegative alternate distribution in eight quadrants. The numerical value of the gravityvariation is much bigger than the gravity gradient variation. The gravity variation andgravity gradient variation are both very small when the vertical position of the space pointis within1km. (3) The gravity gradient in China mainland is computed using GOCE gravity fieldmodel data for the first time. The results show that Tzzis the biggest gradient and Txzisthe smallest compared with the others in Local North Oriented Frame.T rris the biggestgradient andTθ λis the smallest compared with the others in Earth Fixed ReferenceFrame. Comparing with the result computed using GRACE data, the new result canreflect the detail characteristics of the topography and has good consistency with thedistribution characteristics of the geological tectonics.(4) The high precision and high spatial resolution global gravity anomaly, globalgeoid are computed using GOCE data for the first time. The relationship among thegravity anomaly, geological tectonics and partial epicenter in China mainland and Japanstrong earthquake region are analyzed in detail. The result shows that the gravity anomalycomputed by GOCE data has good consistency with the geological tectonics and canreflect the distribution characteristics of the tectonics. The earthquake usually occurred inthe deep gradient zone.(5) The crustal thickness in China’s mainland is inversed by GOCE gravity fieldmodel for the first time. The result shows good consistency with the acknowledgedresearch results.(6) Global gravity anomaly variations are computed using GRACE gravity filedmodel data. The gravity variation characteristics of the Wenchuan (Ms8.0)、Japan(Ms9.0)、Yindu (Ms6.8) are mainly investigated. Take Yindu earthquake as an example,the gravity anomaly of the epicenter (Sikkim) changed6×10-8ms-2approximately. Thephenomenon may be relevant to accumulation of the crustal stress. In order to analyze thecharacteristics of gravity variation before and after the earthquake, the GRACE temporalgravity gradient data are used. The simulating graph shows that the Tzz direction (radialdirection) is more sentive than the other directions.