Waveform observation of pre-earthquake electromagnetic radiation in LF band using capacitive circular flat plate antennas

There have been many reports on pre-earthquake electromagnetic radiation in LF band. However, they are mostly investigated in the intensity of narrow band pulses and there are less discussion on source location. Therefore, we are developing an LF broadband interferometer capable to waveform and spatio-temporal estimation of electromagnetic radiation sources using capacitive circular flat plate antennas. In this paper, preliminary results in waveform analysis, a case study on relationship between unusual waveform and local moderate earthquakes, and performance of interferometer are demonstrated. Analysis of the waveform data observed by the interferometer elements showed that the system successfully recorded LF/VLF waveform signals caused by cloud-to-ground discharges. LF band signals different from the above waveforms were also detected. Although it is possible that these signals were caused by intracloud discharges, we found that we cannot dismiss the possibility that these signals were related to earthquakes.