Deduction of meta-instability of the Yangbi Ms6.4 earthquake in May 2021

The meta-instability experiment provides a theoretical basis for the extraction of precursor information and the study of earthquake prediction. To study the precursor information of earthquakes, the apparent wave velocity ratio of earthquakes with a longitude of E98°–E102° and latitude of N24°–N28° before the Yangbi Ms6.4 earthquake on May 1 to 21, 2021, was calculated based on experiment results of the relationship between seismic wave velocity and stress. Regional gridding was achieved by interpolation, and the gradient of the apparent wave velocity ratio field and its divergence were analyzed. Energy was found to have been released at points (N26.10°, E99.59°) and (N25.73°, E99.87°) as the center, with a connecting line strike of 145°. Energy was absorbed at multiple points along the axis of the line connecting points (N25.81°, E99.59°) and (N26.58°, E100.26°), with a strike of 38°. Precursor information is a characteristic of meta-instability. According to the meta-instable theory, an earthquake will occur near points (N26.10°, E99.59°) or (N25.73°, E99.87°) or on the line connecting them within 0 to 5 days. The rupture length of the fault was about 49.8 km, which, when converted to Ms6.8, is ideal for comparison with the measured Ms6.4 earthquake that had occurred at point (N25.67°, E99.87°). It is believed that this method can provide a reference for the study of precursors of shallow strike-slip earthquakes with a certain number of foreshocks.