关键词: gPhone重力仪, DF地脉动信号异常, 2021年德保M_S4.8地震, 预报效能评估

Abstract: Following the 2019 Jingxi M_S5.2 earthquake in Guangxi, the Debao M_S4.8 earthquake occurred in western Guangxi on August 4, 2021. To investigate the enhancement of seismicity in western Guangxi and determine whether there were any abnormal changes related to the earthquake before it occurred. In this paper, the R-value scoring method is used to analyze the abnormal characteristics and evaluate the prediction efficiency of the vertical displacement of the DF microseism signals and the absolute value of the monthly extreme rate at Pingxiang station. The results show that earthquakes with magnitudes greater than M_S4.0 within a 400 km radius of the Pingxiang station are more likely to occur during periods of high vertical displacement, which frequently coincide with typhoon seasons. These earthquakes are also likely to occur during the transition from low to high vertical displacement values. The 2021 Debao M_S4.8 earthquake occurred during a period when vertical displacement gradually increased from a low value of 0.1×10^-6 m to 0.15×10^-6 m. The results of annual scale prediction efficiency show that, with a monthly rate threshold (S₀) of 0.00039×10^-6 m per month, the optimal value (R_M) was 0.29. The duration of anomalies before the 2021 Debao earthquake lasted 8 months, comparable to the optimal prediction duration of 6 months as determined by the R-value evaluation method. When discussing the accumulation pattern of the R-value with the accumulation of seismic cases, it was found that new seismic cases can improve the optimal prediction strategy, with the threshold gradually converging to 0.00039×10^-6 m per month~0.00031×10^-6 m per month, the optimal forecast duration gradually converging to 6~10 months, and the R-value gradually converging to 0.29~0.31. Comparing with other gPhone gravity stations in Guangxi, it was found that during the 2021 Debao M_S4.8 earthquake, the short-term increase in vertical displacement at Pingxiang station before the earthquake was related to the enhancement of DF pulsation signals excited by the typhoon. The possibility of earthquakes was high when the typhoon path was orthogonal to the coastline of China. This study provides empirical insights and references for predicting the occurrence period of M_S4.0 and above earthquakes in western Guangxi in the future.

Key words: gPhone gravimeter, Anomalies of the DF microseism signals, The 2021 Debao M_S4.8 earthquake, Prediction effectiveness evaluation