It has been found that groundwater levels may function as a sensor for detecting crustal strain. Kyoto University and Kumamoto University analyzed long-term observation data of groundwater levels before and after the Kumamoto Earthquake (April 2016) and clarified this.
The Kumamoto region uses abundant groundwater as its water source, so there are many observation wells that continuously record data on water levels and water quality. This research group hypothesized that fluctuations in groundwater levels (residual components) after removing the effects of precipitation, atmospheric pressure, and global tides are related to crustal strain. The data were analyzed.
The results showed that while the residual component of groundwater levels continued to decline after the Tohoku Pacific Coast Earthquake in March 2011, it began to rise from around 3 until the Kumamoto Earthquake. This decrease is interpreted to be due to stress release, and the increase is interpreted to be due to increased crustal strain. It was also found that the fluctuation pattern of the groundwater level residual component is consistent with the crustal deformation pattern based on observation data from the Global Navigation Satellite System (GNSS).
In addition, the wells that showed a residual component that was particularly clearly related to crustal strain were found to have groundwater inlets (strainers) located in the Togawa lava, which is porous and has high permeability and is the main aquifer. I also learned that. Therefore, it is thought that groundwater levels in porous and highly permeable aquifers respond more sensitively to crustal strain.
The results of this study can be said to demonstrate the possibility of understanding changes in crustal strain through detailed observation of groundwater level fluctuations in porous and highly permeable aquifers. In the future, we will improve accuracy through comprehensive interpretation that combines groundwater level fluctuations, geochemical observations such as water quality and gases originating from deep in the earth's crust, and geophysical observations such as satellite navigation systems (GNSS) and microseismic activity. It is expected that research will develop into the evaluation of crustal deformation.
Paper information:[Scientific Reports] Detecting groundwater level changes related to the 2016 Kumamoto Earthquake
