Anomaly characteristics of Shanxi geomagnetic array data before Yuanping M4.2 earthquake

Shanxi Earthquake Agency and Institute of Geophysics, China Earthquake Administration cooperated to build a geomagnetic array by deploying five sets of GM4 fluxgate magnetometers to obtain the three components magnetic observation data of the regional site on both sides of the Hengshan fault zone in northern Shanxi from September 2014. The geomagnetic array had been operated normally during this period. The completeness and internal quality of recorded data meet the expected standards. On April 7, 2016, a M4.2 magnitude earthquake occurred in Yuanping, about 20 kilometers away from the nearest Daixian measuring point of the geomagnetic array. Through the analysis of the 12-month data from October 2015 to September 2016 by using three methods of correlation, load-unload response ratio and polarization, it is found that the data from each measuring point 3～6 months before the earthquake showed anomalies, among which the correlation of Daixian and Fansi measuring points is the worst. The load-unload response ratio (3.9) of Daixian measurement point exceeds the threshold of 3.5. The polarization value of each measuring point has a high value change two months before the earthquake, but only Daixian measuring point has a high value change one month before the earthquake. The abnormality is very obvious. In the author’s opinion, compared with the magnetic anomalies observed at a single station, this study of multiple observation points and multiple methods has improved the reliability, and provides a reference basis for the future multidisciplinary and multi-method joint earthquake prediction research.