Anomaly detection of environmental electromagnetic wave based on time fluctuation and cross-correlation in magnetic field azimuth

Anomalous radiation of environmental electromagnetic waves is reported as a portent of earthquakes. Then, we are observing environmental electromagnetic waves of the ELF range all over Japan. We have been regarding the high amplitude in the observed signal as anomalous radiation. However, the observed signal contains a lot of low amplitude anomalies hidden by background noise. These anomalies also have the possibility with significant information of a portent of an earthquake. In this paper, we propose the method of detecting anomalous radiation using time fluctuation in magnetic field azimuth which doesn´t depend on the amplitude level. Moreover, we show that an anomalous radiation is the portent of earthquakes by calculating an azimuthal cross-correlation among two or more observation sites.