Time: 10:00a.m.-11:30a.m. 3rd September (Monday)
Venue: Lecture Hall 221, ISESS (Building No. 16), Tianjin University
Speaker: Yuji Sano Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan.
Abstract: Geochemical monitoring of groundwater and soil gas emission pointed out precursor and/or coseismic anomalies of noble gases associated with earthquakes, but there was lack of plausible physico-chemical basis. A laboratory experiment of rock fracturing and noble gas emission was conducted, but there is no quantitative connection between the laboratory results and observation in field. We have reported deep groundwater helium anomalies related to the 2016 Kumamoto earthquake (M7.4), which was an inland crustal earthquake with a strike-slip fault and a shallow hypocenter (10 km depth) close to highly populated areas in Southwest Japan. The observed helium isotope changes, soon after the earthquake, were quantitatively coupled with volumetric strain changes estimated from a fault model. That can be explained by experimental studies of helium degassing during compressional loading of rock samples. Similar changes of helium isotopes were observed at the 2016 Tottori earthquake (M6.6) in Southwest Japan, which was also shallow inland earthquake. Groundwater helium is considered as an effective strain gauge. At the Tottori earthquake, significant oxygen isotopic anomaly relative to the local background measured in groundwater was observed a few months before the M 6.6 earthquake. Samples were deep groundwater located 5 km west of the epicenter, packed in bottles and distributed as drinking water between September 2015 and July 2017, a time frame which covers the pre- and post-event. Small but substantial increase of 0.07‰ was observed soon after the earthquake. Laboratory crushing experiments of aquifer rock aimed to simulating rock deformation under strain and tensile stresses were carried out. Measured helium degassing from the rock and 18O-shift suggest that the co-seismic oxygen anoma
