2013年岷县6.6级地震前天水台磁通门秒数据异常提取分析

Extraction and Analysis of Anomalies of the Second Data from GM4 Fluxgate Magnetometer at Tianshui Station before the 2013 Minxian M_S6.6 Earthquake

基于GM4磁通门磁力仪秒数据,分析研究了2008—2014年天水地磁台的地磁极化值和转换函数变化,结果表明在2013年岷县6.6级地震前天水台地磁极化值和转换函数存在不同程度的异常：（1）转换函数A和B在震前均出现了下降-转折-上升的异常变化,在上升至最高点时发生了岷县6.6级地震;（2）较短的周期转折上升变化更明显,幅度也更大,如｜A｜的20～80s和B的20～110s;（3）3.20s、50s和80s周期的帕金森矢量方位角在震前出现转向并指向震中的现象;（4）4.5～100s周期的极化值Yzh在震前3个月出现2次超3倍均方差的高值异常。

On July 22,2013,an earthquake occurred in Minxian County,Gansu Province,whose epicenter was located 154 km from the Tianshui seismic station.Geomagnetic three-component second sample observations at Tianshui station were initiated in 2007 through a GM4 fluxgate magnetometer.Here,we analyze the change of the geomagnetic polarization value and the transform function at Tianshui station from 2008 to 2014based on the second data of GM4 fluxgate magnetometer.The results indicate that the geomagnetic polarization value and the transform function show different degrees of anomaly before the Minxian M_S6.6earthquake.（1）The transform function exhibited down turning recovery before the earthquake.In fact,the earthquake occurred just as the transform function reached the maximum.（2）The short-term increase was more obvious than the long-term trend,and the rising amplitude was larger.（3）Before the earthquake,the Parkinson vector azimuth in the periods of 20 s,50s,and 80 swas rotated and directed to the epicenter.（4）In April 2013,three months before the earthquake,the geomagnetic polarization at Tianshui station showed two anomalies of high values exceeding three times the mean square deviation.