[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-P12] Attempt to detect pre-earthquake electromagnetic LF radiation by waveform analysis and pulse count survey

*Ota Yuichiro¹, Kenshin Miura², Chie Yoshino³, Katsumi Hattori^3,4,5, Noriyuki Imazumi⁶ (1.Graduate School of Science and Engineering, Chiba University, 2.Faculty of Science, Chiba University, 3.Graduate school of Science, Chiba University, 4.Center for Environmental Remote Sensing, Chiba University, 5.Research Institute of Disaster Medicine, Chiba University, 6.The Institution of Professional Engineers, Chiba Branch, Japan)

Recently, there have been reports of earthquake precursor phenomena related to the LF band. One example is the report by Yamada and Oike, 1996 of an increase in the number of LF pulses at the Uji station prior to the Hyogo-ken Nanbu earthquake. However, some of the increased pulses were later reported by Izutsu 2007 to be due to lightning activity. Discriminating LF-band electromagnetic emissions caused by lightning activity and earthquake-related is a challenge. On the other hand, the development of interferometer is possible nowadays because of the development of ICT and GPS technologies compared to those days. Therefore, we started to develop an LF-band broadband interferometer capable of spatio-temporal estimation of LF-band electromagnetic wave sources. A capacitive circular flat plate antenna (diameter 33 cm, made of aluminum, time constant 30 µs, lower frequency limit 5.3 kHz) was used as the interferometer element antenna. The circular flat-plate antenna has the advantage that it is less likely to generate corona discharges, which can be noisy for detailed waveform observation. The received signal passes through a 500 kHz low-pass filter and is converted to AD with a sampling frequency of 4 MHz and a resolution of 16 bits.
In this study, we investigated two things for weak amplitude pulses using one interferometer element. First, waveform analysis. This eliminated pulses that did not seem to be related to the earthquake. Second, pulse count survey. After waveform analysis, we investigated the relationship between "the pulse number variation of pulses that we assumed to be associated with earthquakes" and "earthquakes that occurred". The details will be given in the presentation.