Study On The Features Of Tectonic Activities Of North China Based On Isostatic Gravity Anomaly

Isostatic gravity anomaly can be acquired by applying latitude correction，fee-airreduction, bouguer reduction and isostatic reduction to the observed value of gravityat a point. It reflects abundant geophysical information, can be used to study massdistribution and equilibrium situation of the crust. Scientists have done manyresearches on the correlation of isostatic anomaly and tectonic movement since1940s,and the results indicated that isostatic gravity anomaly is closely related to tectonicmovement.The north China area (107°～125°E，29°～42°N) is a densely populated,economically developed as well as earthquake-prone area. Earthquakes have caused ahuge loss both of life and wealth in this area for a long time. Research of theequilibrium situation and its correlation to tectonic movement can be useful foridentifying the laws of earthquake activities and studying the earthquake trend in thisarea. High-resolution isostatic gravity anomaly map of the north China area can becalculated with the releasing of precise earth gravity model (EGM) and digitalelevation model (DEM). Against this background, the main works and conclusions ofthis paper are summarized as follows:1) Introduced the origination, development and content of isostasy. Discussed thecalculation and geophysical meaning of isostatic gravity anomaly;2) Analyzed current computation methods, provided an appropriate method tocompute isostatic anomaly from EGM2008and ETOPO1and realized the method byprogramming. Obtained the free-air anomaly map, bouguer anomaly map and isostaticanomaly map of the north China area with a resolution of5′×5′;3) Collected geophysical information of the north China area. Discussed thetectonic structures, neotectonic movement characteristic and tectonic movementcharacteristic of north China area;4) Combining with the geological structure characteristic, discussed the free-airanomaly characteristic, bouguer anomaly characteristic and equilibrium situation ofnorth China area and the emphasis is on the correlation of isostatic anomaly andtectonic movement.Research shows that it’s feasible to get isostatic anomaly from EGM2008andETOPO1, the isostatic anomaly map can reflect the equilibrium situation of northChina area. Results indicate that isostatic equilibrium has generally been achieved inNorth China area, with some unequilibrium local areas. The equilibrium situationgenerally reflects the neotectonic characteristics. There is some connections betweenisostatic anomaly and tectonic movement in north China area, earthquakes tend tooccur in the unequilibrium area and steep gradient belt of isostatic anomaly, and theseareas should be paid more attention.