Joint adjustment of strain rate fields and its application in shallow seismicity forecast in the Sichuan-Yunnan region, China

Calculation methods for large-scale strain rate fields from GNSS horizontal velocity can be divided into two types, namely mathematical and physical methods, which reflect different characteristics of the strain rate field. Therefore, it is necessary to combine these two types of methods to obtain a more reasonable strain rate field. In this study, strain rate fields made from the least-squares collocation (mathematical method) and fault model (physical method) were jointly processed by using Helmert variance component estimation, and the reliability of the joint results was analyzed based on the simulated and measured GNSS velocity. Then, the effect of station density on the strain rate field in the Sichuan-Yunnan region was analyzed, and the results show that the mathematical method was influenced by station density significantly. Based on the joint strain rate field in the Sichuan-Yunnan region, shallow seismicity forecast rates was calculated in conjunction with the Global Centroid-Moment-Tensor Earthquake Catalogue from 1976 to 2021. The results indicate that the shallow seismicity forecast rates of the Sichuan-Yunnan region is high, with 3 Mw ≥ 7.0 earthquakes may occur every 100 years.