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日本地质调查所在近畿及其周边地区设立了一个为地震预测研究服务的地下水观测网,它主要由沿活断层分布的21个观测点组成,分布区域为北纬34°～35.5°,东经134.5°～136.7°。这些观测井是由日本地质调查所在1995年兵库县南部地震(阪神地震)后重新设立的,所有观测井从1998年开始连续观测。2001年3月24日的芸予地震(M6.7)就发生在该观测网以西近海,震源深度51 km,震中离最近的观测井约170 km,最远的约380 km。尽管许多观测井都观测到了地下水位和地壳应变的同震或震后的变化,但都没有明显的震前变化。分析观测结果显示,这些同震和/或震后的变化,可通过由断层模型估计的同震体应变变化得到很好的解释。通常同震和/或震后的地下水位改变由两个因素引起,一个是同震应变变化,另一个是强地面运动,强地面运动使含水层产生裂纹,有时还会发生液化。当发生的地震相对较深并远离观测网时,那么在观测网范围内的地面运动将会很小。因此推断,由应变引起的同震和/或震后地下水位变化比其他因素引起的水位变化大。
The Japan Institute of Geological Survey established a groundwater observation network for earthquake prediction research in and around Kinki, which is mainly composed of 21 observation points distributed along the active fault. The distribution area is 34 ° ~ 35.5 ° N and longitude 134.5 ° ~ 136.7 °. These wells were re-established by the Japan Geological Survey after the 1995 Southern Hyogo Earthquake (Hanshin Earthquake), and all wells were observed continuously since 1998. The Yunyu earthquake (M6.7) occurred on March 24, 2001, just west of the network. The focal depth was 51 km. The epicenter was about 170 km away from the nearest observation well and the farthest distance was about 380 km. Although many observations have observed either coseismic or post-seismic changes in groundwater level and crustal strain, there are no significant pre-seismic variations. Analysis of the observations shows that these co-seismic and / or post-earthquake changes can be well explained by the changes in the coseismic body mass estimated from the fault model. Normally, the co-seismic and / or post-earthquake groundwater level changes are caused by two factors, one is the coseismic strain change and the other is strong ground motion. Strong ground motion causes the aquifer to crack and sometimes liquefy. When the earthquakes that occur relatively deep and away from the observation network, then the movement within the scope of the observatory will be very small. Therefore, it is inferred that the change of coseismic and / or post-earthquake groundwater level caused by the strain is larger than that of other factors.