Abstract
Infrasound waves can be defined as the sound waves with frequency range
from 0.003 to 20 Hz. Kochi University of Technology (KUT) Infrasound
Sensor Network contains 30 infrasound sensors which are distributed all
over Japan, a large number of sensors are located in Shikoku Island, all
infrasound stations installed with accelerometers to measure the peak
ground acceleration (PGA) which can be a good detector for infrasound
sources occur on or under the ground like earthquakes. Many earthquakes
detected by our network after establishing of the network since 2016. In
this study we will focus on all the possibilities for infrasound
detection from earthquakes using KUT sensor network and International
Monitoring system (IMS) stations for the earthquakes which were detected
in southern of Japan during 2019. The selected events for this study are
recorded in different international databases; Reviewed Event Bulletin
(REB) database of International Data Center (IDC) , Japan Meteorological
Agency (JMA) and United States Geological Survey (USGS). There are
different scenarios for infrasound coupling from earthquakes one of
these scenarios is the conversion of seismic waves to acoustic from the
generated T-phases of oceanic earthquakes. On 09 of May 2019, at
23:48:00 UTC an earthquake with magnitude 6.0 mb happened in west of
Kyushu Island and infrasound sensors recorded a clear P-waves, However
station K53 and I30JP recorded infrasound waves at distances ranges
between 850 to 870 km, In addition to T-phases well-recorded from the
earthquake in H11N station near Wake island at 3750 km from the event.
Progressive multi-channel cross correlation method applied on both
infrasound and hydroacoustic data to identify the arrival phases and the
back-azimuth of the waves from station to the source. Moreover,
infrasound propagation simulation applied to the event to confirm the
infrasound arrivals. Ground to Space Model (AVO-G2S) used with HWM-14
and NRL-MSISE to construct the atmospheric profile for higher altitudes
up to 180 km over the event area, furthermore the 3d ray tracing process
and the calculation of the transmission loss equation by normal modes
and parabolic equation methods applied. In conclusion this study shows
the earthquake detectability from infrasound waves using local
infrasound sensors for the largest earthquakes occurred in southern of
Japan during 2019. Many parameters control the generation of infrasound
from earthquakes; magnitude, depth, mechanism and the topographic
features. In addition to the T-phases generation through the SOFAR layer
can be an evidence of seismic conversion to sound for the oceanic
earthquakes as occurred on the earthquake of 09 May 2019, after applying
the propagation simulation with (AVO-G2S) model on this earthquake the
tropospheric arrivals confirmed and the calculated celerities
well-correlated with the real detected data .