Dynamic variation of the gravity field in the Sichuan-Yunnan region and its implication for seismic risk

Using the gravity remeasurement data from 2011 to 2014 in the Sichuan-Yunnan region, We have systematically analyzed the spatial-temporal variations of the regional gravity field and their relation to the occurrence of the Yiliang M(S)5. 7 earthquake in 2012, Lushan M(S)7.0 earthquake in 2013, Ludian M(S)6. 5 earthquake and Kangding M(S)6. 3 earthquake in 2014. Combined with GPS data and leveling observations and regional geologic structure, the time-space distribution of the gravity field and its mechanism were further studied, and its implication for seismic risk is discussed. The interannual variation of gravity dynamic change in the Sichuan-Yunnan region during 2011 to 2012, 2012 to 2013, 2013 to 2014 and the accumulation change during 2011 to 2014 are analyzed. And we have discussed the evolution characters of the gravity field. Combined with regional gravity field variation and seismic activity, and with GPS data during 2011 to 2014, and leveling data during 1971 to 2011, we have found the relationship between strong earthquake and gravity variation in recent years. And on this basis, combined with regional geology structure, we further assess the seismic risk in the Sichuan-Yunnan region in the future. The results show that gravity variation is closely linked with the fault activity in the Sichuan-Yunnan region. It is caused by material migration accompanying active faulting and crustal tectonic motion. The gravity data from the survey area since 2012 have obvious response to four major earthquakes (M-S>5. 7). Regional gravity anomalies and a gravity gradient change may be a seismic precursor. Dynamic evolution characteristics of the gravitational field roughly reflects the dynamic effects of the moving material of the Tibetan plateau which spread toward east and the Longmenshan fault zone by the crust uplift, where compression rates and gravity change are most significant. The spatial distribution of the gravity field and its changes over time and vertical and horizontal crustal movement and tectonic activity observations have certain corresponding relationships. To utilize the remeasurement data to regional gravity change, we have researched its relationship with seismic activity. Gravity dynamic variation has important implications for location prediction of earthquakes, providing experience and reference for medium-term forecast. Earthquakes are easy to occur in four quadrant distribution centers of gravity change or high gradient belts of positive and negative anomalies. Some areas of gravity anomalies have medium-long term seismic risk.