Abnormal characteristics and effectiveness evaluation of the micro-seismic signal before the Debao MS4.8 earthquake

The Debao M_S4.8 earthquake occurred in western Guangxi on August 5, 2021, near where the Jingxi M_S5.2 earthquake occurred in 2019. To study the increasing seismicity in western Guangxi, it is necessary to determine whether there was an anomaly related to the earthquake source near the Pingxiang gravity station, which is located approximately 100 km from the epicenter of the Debao M_S4.8 earthquake. In this study, the R-value scoring method was used to analyze the anomaly and evaluate the prediction efficiency of the double frequency (DF) micro-seismic signal vertical displacement (referred to as vertical displacement, VD) and the absolute value of monthly extreme rate (referred to as the monthly rate). Results show that earthquakes larger than M_S4.0 in the 350 km range from the Pingxiang station tend to coincide with yearly typhoons, and the VD of micro-seismic signals correspondingly changes from low to high. The Debao M_S4.8 earthquake occurred during a gradual VD increase from 0.05 × 10⁻⁶ to 0.10 × 10⁻⁶ m. When discussing the relationships among R, the rate threshold, and the effective duration of prediction, the rate threshold of the micro-seismic signal converges from 0.00039 × 10⁻⁶ to 0.00031 × 10⁻⁶ m/month, the effective duration of prediction is approximately 6–10 months, and R also converges from 0.29 to 0.31. By comparing the results of three gPhone gravity stations in Guangxi, we found that the increase of short-term VD before the Debao earthquake was related to the enhancement of the DF micro-seismic signal excited by the typhoon. When the typhoon track was perpendicular to the coastline of China, the possibility of an earthquake occurring was increased. This study provides evidence and reference for the future occurrence period of earthquakes above M_S4.0 in western Guangxi.