[S-CG47] Crustal fluids and deformation

[SCG47-P02] Coseismic hot spring water changes at the observation stations in San-in region

*Tatsuya Noguchi¹, Yuichi Kitagawa², Takao Kagawa¹, Ryohei Nishida (1.Faculty of Engineering, Tottori University, 2.AIST)

Keywords:hot spring water, water temperature changes, water level changes, San-in region

The water temperature and water level of hot spring water at up to 15 points in the San'in region have been observed since 2002 after the 2000 Western Tottori prefecture earthquake, with an accuracy of 0.01 °C. The water level and temperature measurement interval is 10 seconds, and one-minute average values have been recorded. Water temperature and water level observations continue at three points (Tottori Onsen, Iwai Onsen, and Yutani Onsen) as of February 2024. Water temperature and water level changes have been observed after earthquakes of M6.5 class or greater, and particularly large changes were observed after the 2011 off the Pacific coast of Tohoku earthquake, the 2016 central Tottori earthquake, and the 2024 Noto Peninsula earthquake. The amplitudes of the seismic motions are found to be large in the period range of 1 to 20 seconds. However, in 2016 central Tottori earthquake, changes were observed even at points where no changes were observed in other earthquakes, indicating that strong ground motions (maximum intensity of 6 or higher) have a strong influence on the ground motions. The number of days between the coseismic change and the return to normal temperature corresponded to the magnitude of the temperature change. The water temperature change at Iwai Onsen was (1.7°C increase) 227 days for the 2011 off the Pacific coast of Tohoku earthquake and (1.34°C increase) 177 days for the 2016 earthquake in central Tottori.