[S-VC30] 火山の熱水系

[SVC30-P03] Passive Seismic Survey for Geothermal Exploration in Kirishima Volcanic Complex

*Ehsan Jamali Hondori¹、Guillaume Doudou Faye¹、Muhlash Hada¹、Takuya Yamato²、Yoshihiro Maruyama¹ (1.Geoscience Enterprise Inc. 、2.Geothermal Development and Investment Inc.)

キーワード：Geothermal, Passive Seismic, Fault, Fracture

Geothermal energy is one of the reliable resources with a promising role in reducing CO₂ emission by energy transition toward renewables. There is a high potential of such resources all over Japan, however, geoscientific surveys are required to investigate the subsurface structures and delineate the optimal development plans. Kirishima volcanic complex, located in southwest Japan, is a favorable site for geothermal exploration as previous studies have shown evidence of hydrothermal activities such as mineral alterations and high-temperature fluid observations in several wells. We have installed a seismic network composed of 10 stations to continuously observe the seismic activity around a major fault in the vicinity of the volcanic complex. The objective of the passive seismic survey is to monitor the background seismicity of the area, and also to identify the subsurface fracture network which could be exploited as hydrothermal fluid conduits. The seismic events are extracted from the continuous waveforms by using an automatic triggering approach. P- and S-wave arrival times are picked manually, and source location of the events are calculated using a collapsing grid search method. A layered seismic velocity model approximately inferred from tomographic inversion of Hi-net data (Matsubara et. al, 2019) and an active seismic survey (Tomatsu et al., 2001) is used to build a travel time lookup table of the seismic rays. The resulting hypocenter location of the events clearly show the fault in the NW-SE direction. Additionally, another faulting pattern with a NE-SW trend is identified by the seismic events. Both faulting regimes have been confirmed by geological field surveys. We believe these faults play a key role in the hydrothermal fluid circulation in the subsurface. Our future work is to continuously monitor the faults and fracture network activity.
Keywords: Geothermal, Passive Seismic, Fault, Fracture
References:
Matsubara et. al, 2019, Seismic velocity structure in and around the Japanese Island arc derived from seismic tomography including NIED MOWLAS Hi-net and S-net data, Probing Earth System, IntechOpen, 1-19, doi:10.5772/intechopen.86936

Tomatsu et al., 2001, Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, southern Japan, based on finite difference calculations of complex traveltimes, Geophys. J. Int. 146, 781–794.