title: Horizontal sliding of kilometre-scale hot spring area during the 2016 Kumamoto earthquake.
abstract: We report horizontal sliding of the kilometre-scale geologic block under the Aso hot springs (Uchinomaki area) caused by vibrations from the 2016 Kumamoto earthquake (Mw 7.0). Direct borehole observations demonstrate the sliding along the horizontal geological formation at ~50 m depth, which is where the shallowest hydrothermal reservoir developed. Owing to >1 m northwest movement of the geologic block, as shown by differential interferometric synthetic aperture radar (DInSAR), extensional open fissures were generated at the southeastern edge of the horizontal sliding block, and compressional deformation and spontaneous fluid emission from wells were observed at the northwestern edge of the block. The temporal and spatial variation of the hot spring supply during the earthquake can be explained by the horizontal sliding and borehole failures. Because there was no strain accumulation around the hot spring area prior to the earthquake and gravitational instability could be ignored, the horizontal sliding along the low-frictional formation was likely caused by seismic forces from the remote earthquake. The insights derived from our field-scale observations may assist further research into geologic block sliding in horizontal geological formations.
authors.affiliation: International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.|Department of Earth Resources Engineering, Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tsuji
authors.affiliation: Faculty of Science, Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Jun'ichiro
authors.initials: J
authors.lastname: Ishibashi
authors.affiliation: Fukada Geological Institute 2-13-12 Komagome, Bunkyo-ku, Tokyo 113-0021, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Ishitsuka
authors.affiliation: Chiiki-Shigen-Kaihatsu 2-5-15 Tatsuta Jinnai, Kita-ku, Kumamoto 861-8005, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Kamata