TITLE:
Electromagnetic Precursors to the 2016 Kumamoto Earthquakes
AUTHORS:
Alexander Schekotov, Jun Izutsu, Tomokazu Asano, Stelios Marcos Potirakis, Masashi Hayakawa
KEYWORDS:
Electromagnetic Precursors, The 2016 Kumamoto Earthquakes, ULF/ELF Radiation, VLF Propagation Anomaly, ULF Depression
JOURNAL NAME:
Open Journal of Earthquake Research,
Vol.6 No.4,
September
30,
2017
ABSTRACT:
The Kumamoto area of Kyusyu Island was attacked by a series of large earthquakes
(EQs) in April, 2016. The first two foreshocks had the magnitudes of
6.5 and 6.4, and about 1 day later there was the main shock on 15 April (UT)
with magnitude 7.3. These are fault-type EQs, and so we would expect a variety
of electromagnetic precursors to these EQs because we had detected different
phenomena for the 1995 Kobe EQ, same fault-type EQ. As for the lithospheric
effect, the ULF data at Kanoya observatory (about 150 km from the
EQ epicenters) are used, but the simple statistical analysis could not provide
us with any clear evidence of ULF radiation from the lithosphere. However,
our conventional analyses indicated clear signatures in the atmosphere as
ULF/ELF impulsive emissions and also in the ionosphere as observed by
means of VLF propagation anomalies and ULF depression. ULF/ELF radiation
appeared on 8-11 April (in UT) (maximum on 10 and 11 April (UT)),
while ULF depression took place on 8 and 10 April (in UT), so that both atmospheric
radiation and ionospheric perturbation took place nearly during
the same time period.