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过去对Spitak,Loma Prieta和Guam地震的研究表明,大地震发生之前都会有相应的磁场异常。为了确认这一事实并详细研究超低频(ULF)现象,日本建立了一个超低频磁力仪的监测网络,开展了包括小型台阵在内的网络观测工作。文中同时介绍了在Matsukawa台站观测到的与Iwateken Nairiku Hokubu地震(震级M6.1级,发生在1998年9月3日,震源深度为10 km)相关的地磁资料。分析了4.5年的资料,并对获得的结果进行了讨论。在地震前两个星期,水平和垂直分量之间的谱密度比的(极化)变化表现出异常情况。这是在相当长的数据分析中发现的一次独特的变化,它暗示了这种异常变化可能是大地震孕育期间的一个信号。
Past studies on the Spitak, Loma Prieta and Guam earthquakes show that there was a corresponding magnetic field anomaly prior to the earthquake. In order to confirm this fact and study ULF phenomena in detail, Japan established a monitoring network for the ultra-low frequency magnetometer and conducted network observation work including small arrays. In the meantime, the geomagnetic data related to the Iwateken Nairiku Hokubu earthquake (magnitude M6.1, occurred on September 3, 1998, with a focal depth of 10 km) at Matsukawa station are also presented. Analyzed 4.5 years of data and discussed the results obtained. Two weeks before the earthquake, the changes in spectral density ratio (horizontal polarization) between horizontal and vertical components show anomalies. This is a unique change found in the relatively long data analysis, which suggests that this anomalous change may be a sign of a large earthquake.