It has been known that the preseismic VLF pulse-like electromagnetic signals sometimes increases a few days before the sizable earthquakes especially inland earthquakes. More than two decades ago, the Tokai University group developed a digital recording system and published remarkable results. However, at the time, due to the limitation of personal computer’s data storage and CPU power, they quitted the observation. Therefore, we re-started the research by using the current technology. Fortunately, the “Japanese National Earthquake Prediction Research Project” by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) decided to support our proposal. This is a preliminary report of the development of the new observation system and preliminary results. In this paper, we introduce an electromagnetic wave arrival discrimination algorithm that combines the autoregressive (AR) model and the Akaike Information Criterion (AIC), which are commonly used for automatic waveform reading in seismology, to obtain more detailed arrival times of electromagnetic waves. Then, the source decision was tried using arrival time difference (TDOA - Time Difference of Arrival) of the electromagnetic wave. As a result, several electromagnetic pulses near the epicenter were observed 2 days before the largest inland earthquake (M = 5.6) occurred near the observation network during the observation period. At the present time, these pulses cannot be definitively identified as precursory phenomena, but they are the encouraging result of future observations.

中文翻译：

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VLF波段电磁波观测系统的开发和初步分析-证明短期地震先兆现象

众所周知，地震前的VLF脉冲状电磁信号有时会在大地震特别是内陆地震发生前几天增加。二十多年前，东海大学小组开发了一种数字记录系统，并发表了引人注目的成果。但是，当时由于个人计算机的数据存储和CPU功能的限制，他们退出了观察。因此，我们使用当前技术重新开始了研究。幸运的是，教育，文化，体育，科学和技术部（MEXT）提出的“日本国家地震预报研究项目”决定支持我们的建议。这是有关新观测系统发展的初步报告和初步结果。在本文中，我们介绍了一种电磁波到达识别算法，该算法结合了自回归（AR）模型和Akaike信息准则（AIC）（通常用于地震学中的自动波形读取），以获得更详细的电磁波到达时间。然后，使用电磁波的到达时间差（TDOA-到达时间差）尝试进行源决策。结果，在观测期内在观测网络附近最大的内陆地震（M = 5.6）发生之前2天，震中附近观测到了几个电磁脉冲。目前，这些脉冲尚不能确定地识别为先驱现象，但它们是未来观察的令人鼓舞的结果。