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Because only a small near-field coseismic gravity change signal remains after removal of noise from the accuracy of observations and the time and spatial resolution of the earth's surface gravity observation system, it is difficult to verify simulations of dislocation theory. In this study, it is shown that the GS15 gravimeter, located 99. 5 km from the epicenter of the Ms7. 0 Lushan earthquake on April 20, 2013 at 08 : 04 UTC+8, showed the influence of the earthquake from 2013-04-16 to 2013-04-26 after a time calibration, tide corrections, drift correction, period correction and relaxation correction were applied to its data. The post-seismic relaxation process of the spring in the gravimeter took approximately 430 minutes and showed a 2. 5×10−8 ms−2 gravity change. After correcting for the relaxation process, it is shown that a coseismic gravity change of approximately +0. 59±0. 4×10–8 ms–2 was observed by the GS15 gravimeter; this agrees with the simulated gravity change of approximately 0. 31×10–8 ms–2. The rate of the coseismic gravity change and the coseismic vertical displacement, as measured by one-second and one-day sampling interval GPS units, is also consistent with the theoretical rate of change. Therefore, the GS15 gravimeter at the Pixian Station observed a coseismic gravity change after the Ms7. 0 Lushan earthquake. This and similar measurements could be applied to test and confirm the theory used for these simulations.

Using plane dislocation theory and the seismic-wave inversion results from the Institute of Geophysics, China Earthquake Administration and the Institute of Geodesy and Geophysics, Chinese Academy of Sciences models, the surface coseismic deformation and gravity changes caused by the 2013 Ms7.0 Lushan earthquake are simulated. The simulations of coseismic gravity change and deformation indicate that the dislocation has dip-slip characteristics. The results also show that the coseismic deformation exhibits a symmetrical, positive-and-negative distribution, with the deformation usually being less than 10 mm in the farfield but up to 140 mm in the near-field. The gravity changes are concentrated on the fault-projection area, which is greatly affected by the vertical surface deformation. The gravity change and vertical deformation in the far field are usually less than and 5 mm, respectively, but reach and 330 mm, respectively, in the near field. The simulated results agree well with the measured results, which suggests a theoretical basis for the observed change in gravity before and after this earthquake.

The pattern evolution and dynamic mechanism of the dynamic changes of regional gravity fields occurring before and after the Wenchuan Ms8.0 earthquake are analyzed, based on five epochs of 1998–2007 mobile gravity data from the middle-south section of the north–south seismic belt, and two epochs of field research data collected after the 2008 Wenchuan earthquake in combination with GPS data, leveling observations, and geotectonic environment data. The regional dynamic gravity changes demonstrate the effects of the eastward flow of solid matter in the Qinghai-Tibetan plateau and the preparation of the 2008 Wenchuan earthquake (2–10 yr). The two most meaningful gravity indicators of the Wenchuan earthquake preparation are the positive (increasing) gravity changes occurring over many years in the southwest epicenter and the large-scale gradient zone of gravity variation, with the cumulative difference between the two sides of the gradient zone of gravity exceeding 200 μGal. The positive gravity changes may facilitate a constant energy accumulation and the gradient belt may support seismic shear breakage. Overall, the gravity changes associated with the earthquake preparation indicate a pattern of accelerating increase-decelerating increase-earthquake occurrence. The Songpan-Ganzi block generally displays a negative gravity change, providing evidence for a local upwarping of the deep crust-mantle and an interior expansion of the deep crust attributable to high temperatures. The viewpoint is consistent with the dilatant mechanism for earthquake preparation.

A gravity survey was conducted one month after the 2010 Yushu earthquake in the epicenter area. The cross-fault survey line was 500 km long, from Langqian county to Qingshuihe county, in a transition zone between Bayan Har block and Qiangtang block, in an area of high elevation, large undulating terrain, and complex geological features. An interpretation of the data was carried out together with other kinds of data, such as seismic exploration and magnetic exploration. The result shows that gravity is sensitive to fault boundary; the geologic structure of the region is complex at middle and upper depths, and the density profile reveals an eastward-pushing fault movement.

Based on the data of the repeated gravity observation network in Chinese mainland since 1998, we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7. 3 earthquake. The result shows some mid-to-long term (two to ten years) changes during the earthquake’s preparation. Notable features are a gravity increase lasting several years and a relatively large-scaled gradient zone of gravity change, the former indicating a continuous energy accumulation and the latter a possible location of seismic rupture. These gravity changes showed a trend of increase-accelerated increase-decelerated increase, similar to that of the Tangshan Ms7. 8 earthquake in 1976. The maximum accumulated gravity change related to the earthquake reached 200×10 −8 ms−2.

Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-reflection result. Based on the data of complete Bouguer gravity anomaly and seismic reflection, we obtained a layered interface structure in deep crust down to Moho. Our study showed that the inversion could reveal the interfaces of strata along the survey profile and the directions of regional faults in two-dimension. From the characteristics of the observed topography of the Moho basement, we tentatively confirmed that the uplift of eastern edge of Qinghai-Tibet plateau was caused by the subduction of the Indian plate.

Using the PSGRN/PSCMP software and the fault model offered by USGS and on the basis of finite rectangular dislocation theory and the local layered wave velocity structures of the crust-upper-mantle, the influences of crustal layering and thickness on co-seismic gravity changes and deformation of Wenchuan earthquake have been simulated. The results indicate that; the influences have a relationship with the attitude of faults and the relative position between calculated points and fault. The difference distribution form of simulated results between the two models is similar to that of co-seismic effect. For the per centum distribution, it’s restricted by the zero line of the co-seismic effects obviously. Its positive is far away from the zero line. For the crustal thickness, the effect is about 10% – 20%. The negative and the effect over 30% focus around the zero line. The average influences of crustal layering and thickness for the E-W displacement, N-S displacement, vertical displacement and gravity changes are 18.4%,18.0%, 15.8% and 16.2% respectively, When the crustal thickness is 40 km, they are 4.6%, 5.3%, 3.8% and 3.8%. Then the crustal thickness is 70 km, the average influences are 3.5%, 4.6%, 3.0% and 2.5% respectively.