CAJ | 학술논문

提取了汶川地震前后成都台、木里台和西昌台地磁观测的 Z 分量数据，分3个时段对采样率为每秒一个点的观测数据每小时计算一个最大谱质心、平均谱质心和谱质心标准差。不同台站和不同时段谱质心的结果比较表明，三个参数在汶川地震前这一时段，成都台地磁 Z 分量显示较大的变化幅度，并存在震前逐渐升高的变化趋势，而其它台站和其它时段没有显示如此明显的特征。对比分析表明，成都台地磁 Z 分量显示出的谱质心变化是一个与汶川地震有关联的特征信息，且这一特征的出现与台站和震中的距离有关。对这一问题的深入研究，对于研究震磁关系、大地震的孕震机理，大地震的预测及大震发生位置的推测具有积极意义。
제취료문천지진전후성도태、목리태화서창태지자관측적 Z 분량수거，분3개시단대채양솔위매초일개점적관측수거매소시계산일개최대보질심、평균보질심화보질심표준차。불동태참화불동시단보질심적결과비교표명，삼개삼수재문천지진전저일시단，성도태지자 Z 분량현시교대적변화폭도，병존재진전축점승고적변화추세，이기타태참화기타시단몰유현시여차명현적특정。대비분석표명，성도태지자 Z 분량현시출적보질심변화시일개여문천지진유관련적특정신식，차저일특정적출현여태참화진중적거리유관。대저일문제적심입연구，대우연구진자관계、대지진적잉진궤리，대지진적예측급대진발생위치적추측구유적겁의의。
Research on the seismo-geomagnetic effect goes back more than 100 years,but the use of modern methods and experimentation began in the middle of the last century.Some geomagnet-ically abnormal changes have been reported before large earthquakes,e.g.,the Alaska earthquake (March 27,1964),the Loma Prieta earthquake (M7.1,Oct,17,1989),and the Iwateken Nairku Hokubu earthquake(M6.1,Sep.3,1998).The Wenchuan earthquake was the largest one after the Tangshan earthquake in China.It is important to explore the mechanism of great earthquakes when studying the Wenchuan earthquake.In this paper,we study vertical component (compo-nent) geomagnetic data observed by three stations (Chengdu station (CDP ),MuLi station (MUL),and XiChang station(XIC))in Sichuan Province,with a data sampling rate of one point per second.The maximum spectral centroid,the average spectral centroid,and the spectral cen-troid standard deviation were calculated hourly over three time segments (May 1,2008 to May 12, 2008,May 1,2009 to May 12,2009,and May 1,2010 to May 12,2010).The purpose of this time segment division is,first,to reduce seasonal disturbance,and,second,to avoid interference in the calculated results due to the data length.The results show that among the maximum spectral cen-troid,the average spectral centroid,and the centroid standard deviation,the spectral centroid vari-ability of CDP is greater than the others in the same time period before the Wenchuan earth-quake,and it rises gradually before the earthquake.Other stations did not show these characteris-tics in the same time segments.So we believe there are significant changes in the geomagnetic Z component spectral centroid at CDP,which is information characteristically associated with a great earthquake.This characteristic is also related to the distance from the station to the earthquake position.The distance is 35 km from the epicenter to CDP,357 km from the epicenter to XIC and 400 km from the epicenter to MUL.Our results suggest that these geomagnetically abnormal changes occur in the preseismic period,and can only be measured by a nearby station.Many theo-ries or hypotheses have been put forth to explain the seismo-magnetic phenomena.Generally, earthquake preparation is considered to be a process of the accumulation of stress.When the stress accumulation is more than the elastic limitations of the rock,the rock suddenly dislocates or rup-tures and an earthquake occurs.When media is in the process of stress accumulation,the stress re-distributes spatially,so the media’s elastic deformation changes into nonelastic deformation.Frac-ture morphology and occurrence in space is also changed.A new crack generates,expands and ex-periences fluid infiltration.Rock swelling may be produced that has pressure-magnetic effects,in-duced magnetic effects,rheological-magnetic effects,electric-magnetic effects,thermal-magnetic effects,etc.The existence of abnormal activity before an earthquake is an important issue in the study of great earthquakes.Our intent is not to focus on a discussion of the occurrence mechanism of seismo-magnetic phenomena,but on how to extract anomalous information about an earthquake from the geomagnetic data from a nearby station.Our results show that this type of study can provide important reference data for research on seismo-magnetic effects,earthquake mechanisms, earthquake predictions,and position estimations of future earthquakes.Furthermore,our results indicate that the spectrum centroid may provide a reasonable and suitable source of information prior to an earthquake.