Distribution Of The Crust And Upper Mantle Density By Joint Inversion Of Gravity And Seismic Data

Joint inversion of gravity and seismic has many advantages compared to a singlegeophysical inversion method. This dissertation studies the gravity inversion methodbase on the constraint of the seismic inversion results. Seismic inversion uses seismictomography and gravity inversion uses the ART algorithm.In this dissertation, the processes of the gravity data processing is as follows.Bouguer gravity anomaly data minus the gravity anomaly caused by the fluctuation ofthe deposited layer and the Moho. And then it minus the gravity anomaly caused bythe deep layer source. As a result, residual gravity anomaly which is the base of thegravity inversion will be got. Seismic inversion data from seismic tomography is thepercent of the P-wave velocity perturbation and is converted to density according tothe empirical relation of speed-density which is the density inversion constraint.Finally, we can get the remaining density distribution by the inverse calculation.During the inversion calculation we use the ART algorithm, which can significantlysave the computer’s memory and improve the computing speed.In this dissertation, we calculate the actual data of Northeast China and the wholecountry and the surrounding area. The resolutions of seismic tomography in the twoareas are different. But the results are good. What’s more, we also analysis the resultsaccording to the known geological data and geophysical data. The results show that:gravity-earthquake joint inversion is an effective method. If seismic data is enough,the joint inversion can improve seismic inversion results and reliability. If the area hasless seismic data, the resolution seismic inversion can be greatly enhanced. Theinversion results also show that the density anomaly has strong correlation with thesubsurface structure. Changbai Mountain and Jingbo Lake which are famous volcanoin Northeast China. The shallow layers under them show low density abnormalcharacteristics, but the deep layers show abnormal characteristics of high density,which indicates that the subduction of the Pacific plate. The shallow layers under theQinghai-Tibet Plateau show abnormal low density, and deep layers shows high density anomalies, which suggests the subduction of the Indian plate caused the upliftof the Qinghai-Tibet Plateau.