Groundwater Flow Anomalies Related to the Luding M6.8 Earthquake Identified by the Empirical Mode Decomposition

Groundwater flow is one of the seismic observation items sensitive to seismic reflection. Based on the Luding M6.8 earthquake at 12:52 am on September 5, 2022, this paper analyzes and processes the flow data of Xichang, Zhaojue and Yanyuan stations by empirical mode decomposition (EMD) method. It is found that the occurrence time of anomalies at the three stations is concentrated in the short imminent stage about 4 to 5 days before the earthquake, and the abnormal variation forms are of the "up-down-up" type. The abnormal flow frequency bands of Xichang, Zhaojue and Yanyuan stations are 3.5×10⁻⁷ Hz～3.8×10⁻⁶ Hz, 3.5×10⁻⁷ Hz～3.5×10⁻⁶ Hz and 3.8×10⁻⁷ Hz～3.4×10⁻⁶ Hz. The results show that the EMD method can effectively improve the capability to obtain the abnormal flow information before the earthquake, so it has a good application prospect in the field of groundwater flow anomaly feature identification and signal analysis.