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Hayakawa等(1996)和Miyahara等(1999)利用距离震中67km处的磁力仪记录的1s间隔采样数据,通过极化分析(地磁场垂直分量与水平分量的比值)认定了1993年关岛Mw7.7级地震的前兆性超低频磁异常变化。为了检验他们的结果,我们将他们的数据(GAM)与取自日本柿冈观测台(KAK)的1s间隔数据以及全球地磁活动指数Kp进行了比较,并查看了由美国地质调查局在关岛地磁台的工作人员保存的日志记录。我们有以下发现:(1)Hayakawa等和Miyahara等的数据分析过程都存在问题;(2)GAM地磁台数据、KAK观测台数据和Kp数据之间显著相关;(3)这次地震之前不存在可识别的局部异常信号。我们在极化分析中发现的所谓异常变化只是正常的全球地磁活动的一部分,与这次地震并不相关。
Hayakawa et al. (1996) and Miyahara et al. (1999) used 1s interval sampling data recorded by a magnetometer at a distance of 67km from the epicenter to determine the 1993 Kwangtung Mw7.7 level by polarization analysis (the ratio of the vertical component to the horizontal component of the geomagnetic field) Seismic precursory ultra-low frequency magnetic anomalies. To test their results, we compared their data (GAM) with the 1s interval data from the Kakogawa Observatory (KAK) in Japan and the global geomagnetic activity index, Kp, and reviewed the geomagnetic data obtained by the United States Geological Survey Taiwan staff save the log records. We have the following findings: (1) There are problems with the data analysis process such as Hayakawa et al. And Miyahara et al. (2) There is a significant correlation between GAM geomagnetic station data, KAK observatory data and Kp data. (3) Local anomaly signal that can be identified. The so-called anomaly changes we find in the polarization analysis are only part of the normal global geomagnetic activity and are not related to this earthquake.