Evolution characteristics of precursory anomalies before the M_S6.4 Menyuan，Qinghai，earthquake in 2016

By retrospectively analyzing and sorting out the anomalies before the 2016 Menyuan M_S6.4 earthquake, this paper discusses the spatio-temporal evolution characteristics of precursory anomalies before the earthquake. The results show that the anomalies are mainly concentrated in the region within 300 km around the epicenter. Among all kinds of the anomalies, deformation anomalies appeared first, followed by medium- and short-term fluid anomalies, and electromagnetic anomalies in the impending earthquake stage. The evolution of precursory anomalies appears as stage and migration characteristics in space-time. The variation of pre-earthquake anomalies can be divided into α, β, γ three stages. During the α stage, the precursory anomalies spread from the epicenter to the periphery in the far source field mainly 390−630 days before earthquakes. During the β stage, the precursory anomalies are widely distributed in 100−200 days before earthquakes. During the γ stage, the precursory anomalies of the near-field source spread outwards.