Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan.
Institute for Geothermal Sciences, Kyoto University, Beppu, Oita 874-0903, Japan.
Sci Rep. 2016 Nov 29;6:37939. doi: 10.1038/srep37939.
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 report here deep groundwater helium anomalies related to the 2016 Kumamoto earthquake, which is 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, are quantitatively coupled with volumetric strain changes estimated from a fault model, which can be explained by experimental studies of helium degassing during compressional loading of rock samples. Groundwater helium is considered as an effective strain gauge. This suggests the first quantitative linkage between geochemical and seismological observations and may open the possibility to develop a new monitoring system to detect a possible strain change prior to a hazardous earthquake in regions where conventional borehole strain meter is not available.
地下水和土壤气体排放的地球化学监测指出了与地震相关的稀有气体的前兆和/或同震异常，但缺乏合理的物理化学依据。我们进行了岩石破裂和稀有气体排放的实验室实验，但实验室结果与野外观测之间没有定量联系。我们在这里报告了与 2016 年熊本地震相关的深部地下水氦异常，这是一次内陆地壳地震，具有走滑断层和浅震源（10 公里深度），靠近日本西南部人口密集地区。地震后不久观察到的氦同位素变化与从断层模型估计的体积应变变化定量耦合，这可以通过压缩加载岩石样品过程中氦释放的实验研究来解释。地下水氦被认为是一种有效的应变计。这表明地球化学和地震观测之间的第一个定量联系，并可能开辟一种新的监测系统的可能性，以在常规钻孔应变计不可用的地区检测危险地震前的可能应变变化。
