11:45 AM - 12:00 PM
[SGD01-05] A study of crustal property changes after the northern Osaka earthquake by evaluating the correlation between surface displacements and groundwater level changes
Keywords:the 2018 northern Osaka earthquake, groundwater level displacements, PSInSAR analysis
Interferometric Synthetic Aperture Radar (InSAR) analysis is a rapidly advancing geodetic observation technique that can be used to obtain wide-area and time-series ground surface displacement data. In recent years, InSAR analysis has been widely used as an application for groundwater level monitoring. Previous research results on surface displacements and groundwater level changes have shown that there are correlations between them. There are two types of correlation patterns: seasonal and linear. The famous example of linear correlation is the rapid rise of groundwater level after an earthquake, and the ground surface rises accordingly. On the other hand, many studies have been conducted on the seasonal pattern. Previous studies suggest that the correlation depends on pore water pressure and water mass loading. However, there are few examples of studies on such positive and negative correlation mechanisms of seasonality, so the mechanisms need to be clarified. For example, the characteristics of aquifers (confined or unconfined aquifer) and groundwater extraction conditions are not considered. And there are still no examples of studies that examine how seasonal correlation changes with earthquakes.
In this study, we examine the correlation between surface displacements and groundwater level changes, and evaluate the changes in correlation before and after an earthquake in the Keihan area, which is the area affected by the Mj 6.1 northern Osaka earthquake on June 18, 2018. The surface displacement data was estimated by PSInSAR analysis using Sentinel-1 data of the European Space Agency. Groundwater level observation data from January 1, 2017 to December 31, 2020 at a total of 21 groundwater level monitoring stations published by the Ministry of Land, Infrastructure, Transport and Tourism's Water Quality Database were used. Cross-correlation coefficients were calculated to quantitatively evaluate the correlation.
As a result of PSInSAR analysis, seasonal surface displacement was estimated and high seasonal correlation with groundwater level change was found at many groundwater level stations. The seasonal correlation patterns can be divided into (i) positive correlation, (ii) negative correlation, and (iii) non-correlation, with two groundwater level stations showing positive correlation and 16 groundwater level stations showing negative correlation. The peaks of the correlations, including both positive and negative correlations, appeared approximately every 365 days, and the seasonality of the correlations could be evaluated correctly. No relationship was found between the confined or unconfined aquifer and the seasonal correlation. The positive correlation was observed in the area where groundwater extraction was conducted, suggesting that the connectivity of each aquifer in the ground is related to the positive and negative correlation.
Next, we recalculated the correlations at the groundwater level observation locations before and after the earthquake, and found that the negative correlations increased widely after the earthquake. This may be due to the increase in groundwater volume caused by the increase in permeability and porosity of the ground. In order to test the hypothesis of crustal property change caused by the earthquake, we compared the measured data with the groundwater level model according to the time series of precipitation, and compared the pseudoelastic constants before and after the earthquake using the data of surface displacement and groundwater level change. The results of our study indicate that the northern Osaka earthquake increased the sensitivity to the water mass loading in a wide area due to an increase in the permeability and porosity, which could suggest the mechanism for increasing the negative correlation. As earthquakes in the Mw6.0 class occur frequently worldwide, similar phenomena may have occurred in areas with abundant groundwater resources.
In this study, we examine the correlation between surface displacements and groundwater level changes, and evaluate the changes in correlation before and after an earthquake in the Keihan area, which is the area affected by the Mj 6.1 northern Osaka earthquake on June 18, 2018. The surface displacement data was estimated by PSInSAR analysis using Sentinel-1 data of the European Space Agency. Groundwater level observation data from January 1, 2017 to December 31, 2020 at a total of 21 groundwater level monitoring stations published by the Ministry of Land, Infrastructure, Transport and Tourism's Water Quality Database were used. Cross-correlation coefficients were calculated to quantitatively evaluate the correlation.
As a result of PSInSAR analysis, seasonal surface displacement was estimated and high seasonal correlation with groundwater level change was found at many groundwater level stations. The seasonal correlation patterns can be divided into (i) positive correlation, (ii) negative correlation, and (iii) non-correlation, with two groundwater level stations showing positive correlation and 16 groundwater level stations showing negative correlation. The peaks of the correlations, including both positive and negative correlations, appeared approximately every 365 days, and the seasonality of the correlations could be evaluated correctly. No relationship was found between the confined or unconfined aquifer and the seasonal correlation. The positive correlation was observed in the area where groundwater extraction was conducted, suggesting that the connectivity of each aquifer in the ground is related to the positive and negative correlation.
Next, we recalculated the correlations at the groundwater level observation locations before and after the earthquake, and found that the negative correlations increased widely after the earthquake. This may be due to the increase in groundwater volume caused by the increase in permeability and porosity of the ground. In order to test the hypothesis of crustal property change caused by the earthquake, we compared the measured data with the groundwater level model according to the time series of precipitation, and compared the pseudoelastic constants before and after the earthquake using the data of surface displacement and groundwater level change. The results of our study indicate that the northern Osaka earthquake increased the sensitivity to the water mass loading in a wide area due to an increase in the permeability and porosity, which could suggest the mechanism for increasing the negative correlation. As earthquakes in the Mw6.0 class occur frequently worldwide, similar phenomena may have occurred in areas with abundant groundwater resources.