EGM2008 Model And Ground Gravity Data Fusion And Crustal Density Structure Inversion In The Western Sichuan Region

The western Sichuan region is a complex,earthquake-prone area,it is the main research direction of gravity measurement data applied to seismology by using gravitational data to analyze gravity isostasy,crustal density structure,vertical tectonic stress and its relationship with earthquakes.The vertical tectonic stress is a new method proposed to study the tectonic stress in the vertical direction by using gravity data.Using good gravity data and reliable crustal density structure,studying the vertical tectonic stress of the layered crustal structure will be a good angle and cut point for studying earthquakes.Gravity data is the basis of gravity research,commonly used gravity data from satellite and ground measurements.Measurement technology differences lead to the limitations of both data with spatial resolution and accuracy,the combination of the advantages of the two data will be very good complementarity,providing a good basis for gravitational research.In this study,we will study the regional gravity isostasy,the crustal density structure and the vertical tectonic stress by using the satellite gravity data and the measurement data in western Sichuan,and discuss the relationship between the vertical tectonic stress and the seismic distribution,which provides the basis for the study of crustal tectonics and earthquake prediction in western Sichuan.First,the least squares collocation method of 'erasure-restoration' is used to fuse the gravity data of EGM2008 and ground measured gravity data in western Sichuan,And evaluate the suitability of the fusion method in plain,mountainous and hilly areas.Then,combined with the data of fusion and CRUST1.0 crustal structure model,and use the nonlinear least squares method to invert the crustal density structure of sedimentary layer,upper crust,middle crust and lower crust.Finally,we calculate the isostasy adjustment and the vertical tectonic stress field which considers the crustal structure,and discuss the relationship between the regional seismic distribution and the vertical tectonic stress field.Data fusion results show that satellite and ground measurement data fusion can significantly improve the overall accuracy of regional gravity data,through the data fusion,the accuracy of the gravity data in the western Sichuan region is increased from 20 mGal to about 5 mGal.The results of the crustal density structure obtained by the inversion of the gravity data after fusion are basically the same as those of the predecessor seismic wave results,the results show that the Longmenshan fault is a steep zone with crustal thickness on both sides.The results of vertical tectonic stress show that the vertical tectonic stress is higher in the middle and southern of Longmenshan and the northeastern of Sichuan Basin.The vertical tectonic stress is low in the HuaNan block,which is basically in the crustal equilibrium state.As a whole,in the western Sichuan region from the southeast to the northwest,the vertical tectonic stress presents 'negative-positive' alternately.By comparing the vertical tectonic stress and the earthquakes bigger Ms 3.0 since 1970,it is found that most of the earthquakes occur in the vertical stress range of-20?10 MPa,and all the Ms8.0 or bigger earthquakes occurred in the vertical tectonic stress positive place.The results also show that the seismic distribution is related to the vertical tectonic stress gradient,most of the earthquakes occur in the stress gradient high value area,it shows that the high gradient region is a region with high risk of earthquakes and should be focused.From the distribution of vertical tectonic stress field,it is found that the area of the vertical tectonic stress is high in the southern p of Ya'an,southwest of Songpan and southwest of Kangding,and the seismic hazard is large and should be paid attention to.