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《Seismology and Geology》 2008-02
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STUDIES ON STRATUM DENSITY CHANGES INVERSION IN XI'AN AREA WITH GENETIC FINITE ELEMENT METHOD

ZHU Gui-zhi1,2)SHI Yao-lin2)ZHU Yi-qing1)WANG Qing-liang1)1)No.2 Monitoring Center,China Earthquake Administration,Xi'an 710054,China2)Laboratory of Computational Geodynamics of Graduate School of the Chinese Academy of Sciences,Beijing 100049,China  
Gravity changes are the comprehensive reflection of density changes and deformation in Earth's medium.Gravity gradient changes reflect the change of gravity anomaly,with a resolution higher than the gravity anomaly changes.In this paper,using the gravity anomaly data during 1992—1994 and leveling data during 1988—1991,we compute the gravity anomaly caused by stratum density changes by eliminating Bouguer anomaly with Bouguer correction formula,then inverse the stratum density changes by using genetic finite element method.The gravity gradient changes are also computed in order to analyze the main contribution to the gravity change in the Xi'an area.The results show that the excessive extraction of confined groundwater has led to the confined water level drop,much water was lost and clay layer was compacted,and the resulting land subsidence is the main reason for gravity change.Densification of clay layer in most parts of the aquifer system can generate surplus stratum density,but for several local areas,such as Xiaozhai and Tielumiao areas,excessive extraction of ground water has lowered the groundwater level,resulting in water loss but not densification of clay layer.This is the major cause for some negative gravity changes.But we cannot rule out the contribution of possible activities of fissures in this area.
【Fund】: 地震科学联合基金青年基金(C07053)资助
【CateGory Index】: P631.14
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