【摘要】 本文提出了将主成分分析方法和地磁日变分析方法相结合以从较强干扰背景中提取相对较弱地震地磁信息的一种新思路.具体以1 998年日本岩手县北部6.1级地震为例,选用三个地磁观测台资料进行研究.利用调和分析方法得到了各台基于多次谐波拟合的地磁日变曲线,在此基础上对各台的地磁日变形态进行了研究,发现距震中最近地磁台的日变形态在地震前大约两周出现了明显的异常,而其他两个距离震中相对较远的观测台日变形态基本正常.最后,将主成分分析方法应用于上述拟合地磁日变结果,得到了各主成分及其所占能量比的时间变化,结果表明在地震前两周左右第二主成分所占能量比显著增加,而且距离震中最近的台站的上述变化明显高于另两个较远的台站.上二述结果表明地震前两周左右检测到的地磁日变异常可能与震中附近地下电阻率的变化或孕震过程中产生的电磁信号存在一定关系,相关研究结果有助于加深对地震电磁现象的认识和理解.更多还原

【Abstract】 This study provides a new seismomagnetic data processing method by combining principal component analysis （PCA） and geomagnetic diurnal variation analysis.As a case study, we investigated the geomagnetic data observed at Matsukawa,Kakioka,and Memambetsu stations and discussed their relationship with the M6.1 Iwate-ken Nairiku Hokubu earthquake occurred in 1998.The results showed that there is a clear anomaly of the geomagnetic diurnal variations about two weeks before the mainshock at Matsukawa station,which is only 15 km away from the epicenter.After applying the PCA method to the geomagnetic diurnal data,we investigated the temporal variations of the contribution of each principal component.The results indicated that the contribution of the 2^nd principal components,which may relate with the local underground conductivity structure and/or the local electromagnetic disturbance possibly due to the local seismogenic process,increased significantly about two weeks before the earthquake. These results are consistent with those obtained independently from the previous case studies by using polarization analysis method.This study may strengthen the understanding of seismoelectromagnetic phenomena.更多还原