Six wells were continuously monitored in Hokkaido, northern Japan, to relate groundwater level changes to regional seismic activity. Groundwater level changes following the 2018 Hokkaido Eastern Iburi earthquake were detected in three of the six wells, even though they are located hundreds of kilometers from the epicenter. The groundwater level changes are qualitatively consistent with the volumetric strain induced by the earthquake. We analyzed groundwater level responses to the M 2 tidal constituent before and after the earthquake, but related changes in amplitude and phase shifts remained within the usual variation. Observed coseismic change was explained by the response to the M 2 tidal constituent component and the calculated volumetric strain for one of the wells, where groundwater level decreased. The observed change in the other two was found to be much greater than the corresponding estimates of the volumetric strain.

中文翻译：

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2018 年北海道伊布里东部地震期间地下水位的同震变化

在日本北部北海道连续监测六口井，将地下水位变化与区域地震活动联系起来。在 6 口井中的 3 口井中检测到 2018 年北海道东伊武里地震后的地下水位变化，尽管它们距离震中数百公里。地下水位变化与地震引起的体积应变在性质上是一致的。我们分析了地震前后地下水位对 M 2 潮汐成分的响应，但幅度和相移的相关变化保持在通常的变化范围内。观察到的同震变化可以通过对 M 2 潮汐组成成分的响应和计算的其中一口井的体积应变来解释，其中地下水位下降。