Mining for seismomagnetic information of geomagnetic Z component based on Copula theory

In this paper, we selected geomagnetic data of five seismographic stations in Tianjin, analyzed and calculated geomagnetic Z component data from 1986 to 2013 based on Copula theory. After comparison of Kendall and Spearman coefficients in a variety of models, the optimal model was got, and then Kendall coefficient timing curves were analyzed in different cycles. The calculated results show that Kendall coefficient timing curve is in the disordered phase before the M_S≥5.0 earthquake, and its consistency turns better rapidly after the earthquake. That is because the accumulated seismic stress causes the underground electrical structure to change, and the stress is released after the earthquake, magnetic field data returns to normal. It is more predominant that Kendall coefficient of the Qingguang seismographic station (it has the smallest distance from the epicenter) dropped sharply before the Wen’an M_S5.1 earthquake in 2006, which is different from that of other stations; while Kendall coefficient of the Ninghe seismographic station (it has the smallest distance from the epicenter) rose marginally before the Tangshan M_S4.8 earthquake in 2012.