Using the gravity observation data of Mulanshan short gravity baseline field in 2018 and 2022,we established a high-precision short gravity baseline field of Mulanshan based on the relative gravity joint measurement method under the control of absolute gravity.We also analyzed and discussed the accurate calibration of the monomial coefficient of the relative gravimeter during the construction of the gravity short baseline field,the distribution of gravity values in the gravity baseline field of Mulanshan and the contribution of various environmental factors in the gravity variation results,these results show that:（1） Maximum gravity segment difference of Mulanshan calibration baseline is 102.176mGal from G01 to G03 stations,and the average accuracy of gravity value of each measuring station reaches4.8μGal.The geological structure of the Mulanshan baseline is stable,and the gravity change of measuring stations is not obvious.From 2018 to 2022,the gravity variation range of measuring stations was 5.9～12.8μGal,with an average of 9.5μGal,and the average uncertainty was±5.7μGal.The gravity field mainly showed a positive change.The variation range of gravity in each measurement section is-4.8～6.9μGal,with an average of （1.8±8.6）μGal.The change of the surrounding environment has a certain impact on the gravity field,and the contribution of the new buildings near the G01 and G02 to the gravity change is 3.6μGal and-0.51μGal,respectively.These gravity changes of measuring stations in the IOS and Mulanshan baseline caused by vertical surface movement are（2.17±0.44）μGal and （1.67±0.45）μGal.The gravity effect caused by the change of surface water storage is（1.07±0.84）μGal,which cannot be ignored.Compared with observation results,the gravity change of each measuring station and section after correction is reduced,and the average gravity change values are reduced by 38.2%and 50.8%,respectively.The corrected gravity change results are more accurate.Due to the cumulative effect of errors in the correction process,the uncertainty of gravity change results after correction increases accordingly,and the uncertainty of gravity change results of measuring station and measuring section increases by 2.5%and 2.8%compared with observation results,respectively.Combined with the gravity change results of the measuring station and the measuring section,we can effectively extract abnormal information in gravity dynamic change results.（2） There are differences in monomial coefficients of different gravity sections of the relative gravimeter.The results of CG-6 and CG-5 relative gravimeters are relatively consistent,and there is no systematic deviation between the two gravimeters.The difference in the monomial coefficient between the Wuhan-Yichang section（sub-section） and the Wuhan-Lücongpo section（total section） is4.809‰，which has a great influence on the gravity observation results.The monomial coefficient needs to be accurately measured.The difference of the monomial coefficient in the sub-section is negatively correlated with the proportion of the gravity segment difference in the sub-section to the total section;the monomial coefficient of the total section is a weighted average result of each subsection,and the proportion of gravity segment difference in sub-section to total section is the corresponding weight factor.Accurate calibration of the monomial coefficient of the relative gravimeter is a technical guarantee to obtaining high-precision gravity observation results.The gravity segment difference of sub-segments cannot cover the gravity range of the measurement area due to smaller segment difference,which will lead to the extrapolation of the monomial coefficient,so it cannot effectively calibrate the monomial coefficient of the relative gravimeter applicable to the whole measurement area.The total section can cover the gravity range of the measurement area,and the monomial coefficient is the ratio between the segment difference measured by the relative gravimeter and the known segment difference,and its calibration accuracy is inversely proportional to the gravity segment difference,so when using the total section as a reference for calibration of the monomial coefficient of the relative gravimeter,accuracy of the calibration can be guaranteed and precision of the calibration can be improved,so calibration result of the monomial coefficient using the total section is more accurate.The existing widely used relative gravimeters （such as LCR,CG-5,BURRIS,CG-6,and so on） have time-varying characteristics of the monomial coefficient,weakening the errors caused by changes of the monomial coefficient is essential to improve the accuracy of observations,and corresponding calibration is required before each period of gravity observation.The monomial coefficient of the relative gravimeters needs to be calibrated using a large segment difference,and the segment difference（or the accumulated segment difference） should be greater than300mGal.

Sichuan-Yunnan and its adjacent area are the main places where the eastward material flow from the Tibet Plateau escapes and spins to SE-SSE with active geological formations and frequent seismic activity. The study of the crustal structure and material transport characteristics of this region is important to reveal the mechanism of earthquake occurrence here. It can also deepen the understanding of the tectonic activity mechanism of the southeastern margin of the Tibet Plateau. This paper summarizes recent achievements and important advances in the study of regional Bouguer gravity anomaly and crustal density structure in Sichuan-Yunnan and its adjacent areas. (1) Bouguer gravity anomaly information of eight gravity profiles was obtained by using gravity and GNSS positioning techniques, and the basic framework of crustal density structure of the southeastern margin of the Qinghai-Tibet Plateau and its adjacent areas was constructed by using gravity inversion techniques constrained by various geophysical observations. (2) New gravitational evidence of clockwise rotation of the Sichuan-Yunnan rhomboid massif was found through the separation and extraction of gravity signals by wavelet decomposition and normalized gradient. (3) Through the scientific research of the Yushu MS7.1, Lushan MS7.0 and Ludian MS6.5 earthquakes, we have deepened our understanding of the seismogenic tectonic environment in the southeastern margin of the Tibet Plateau. There are significant differences in density distribution on sides of the left-slip shear fault zone (Ganzi-Yushu, Xianshuihe and Xiaojiang) and the large thrust nappe structure (Longmen Shan), both of which are regional seismicity-controlled faults. The seismicity of the Ludian earthquake zone may be related to the eastward migration of the Xiaojiang fault zone. The nappe characteristics and detachment structure of the Longmenshan fault zone may be an important factor in the occurrence of the Lushan earthquake at the Houshan fault.

为研究三河-平谷地震区浅层构造背景、地震孕育机理及地震与构造的关系，利用高精度重力异常数据，采用基于块体生长模式的重力三维反演算法对地震区浅层三维密度结构进行反演，并通过模拟试算验证基于块体生长模式反演方法的有效性和稳定性。高精度布格重力异常显示，三河-平谷8.0级地震位于大兴重力局部高、三河-马坊重力局部高与大厂重力低之间的交汇过渡低值区域。研究区浅层三维密度结构反演结果表明，1679年三河-平谷M8.0地震明显受NE向夏垫断裂控制，断裂两侧密度差异明显且向下延伸约10 km，推测发震部位深约10 km。