Basic study for electromagnetic phenomena preceded by earthquakes in and around Tokai and Kanto regions

我们在东海和关东地区及其周边地区持续运营着条件良好的电磁监测站。关于地壳形变观测，我们在研究期间部署了大约60个GPS站，这些站由不同的预算支持，以监测东海慢滑事件。此外，我们继续进行了电磁ACROSS的基础实验，这被认为是一种很有前途的方法来监测地下的时间变化。在距离440Am偶极矩信号源40km的远距离观测站，通过两周的数据叠加，成功地探测到了440Am的信号。关于电磁场的水下实时监测，我们与JAMSTEC合作，在Hatsushima岛沿海部署了三分量磁力计和二分量电场计。此时，我们成功地以高采样率（8Hz）进行了一年多的监测，清晰地探测到了同震电磁变化。通过观测，我们认为三分量磁强计是目前最有希望检测直流超低频范围变化的仪器。日本岛，特别是日本中部和东京地区，以直流列车泄漏电流为主的大量人为噪声占主导地位。因此，很难获得高质量的数据。通过对观测数据的分析，我们开发了一些降噪方法（主成分分析、PCA、独立成分分析、伊卡、维纳滤波技术、去趋势波动分析等），针对数据的公开，我们开发了一些初步的分析程序，可以在网站上运行。此时，通过使用IP地址系统来控制一些观察点。

We continuously operate electromagnetic monitoring stations in and around Tokai and Kanto regions with good conditions. Concerning crustal deformation observations, we deployed about sixty GPS stations during the research period, which were supported by a different budget to monitor the Tokai slow slip event. Furthermore, we continued fundamental experiment of electromagnetic ACROSS, which is considered to be a promising method to monitor the temporal change of the underground. In this experiment, we succeeded to detect the signal by data stacking of two weeks in a remote station which was 40km away from the signal source of 440Am with the dipole moment. Concerning the underwater realtime monitoring of the electromagnetic fields, we deployed the three-component magnetometer and two-component electric field meter off the coast of Hatsushima Island in cooperation with JAMSTEC. At this moment, we succeeded to monitor more than one year with high-sampling rate (8Hz) and detected co-seismic electromagnetic changes clearly. Through the observation, we now conclude that the most promising device to detect the precursory changes in DC-ULF ranges is three-component magnetometer.Japanese Island, especially central Japan and the Tokyo areas, it is dominant that a lot of artificial noises mainly on the leakage current from DC-driven trains. Therefore, it is very difficult to obtain good quality of data. Through the observation periods, we developed some noise reduction methods (Principal Component Analysis ; PCA, Independent Component Analysis ; ICA, Weiner filter technique, Detrend Fluctuation Analysis and so on. Concerning the data disclosure, we developed a lot of preliminary analyzing programs which can operate on the website. At this moment, some observation points are controlled by using IP address system.