Evaluation of faults stability due to passing seismic waves: Study case of groundwater level changes induced by the 2011 Tohoku earthquake in Central Japan

IF 3.1 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Pierre Jeanne , Yves Guglielmi , Jonny Rutqvist , Takanori Kunimaru , Hiroyuki Umeki
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Abstract

In the study, we analyze changes in groundwater pressure observed in several boreholes drilled in and around the Mizunami Underground Research Laboratory (MIU) induced by the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0). The aim of this project is a development of methodology to evaluate systematic fault activity by numerical analysis. To reach this goal we investigate the behavior of the fault zones present in the area during the passing of seismic waves. We built a simplified hydrogeological model of the MIU site and performed a series of fluid flow simulations with TOUGH2 flow numerical code. We investigate how changes in permeability along three faults present in the study area: the Tsukiyoshi Fault, the Hiyoshi Fault and the Main-Shaft Fault may have influence the groundwater level monitored in boreholes intervals. We also test the influence of the cone of depression at the MIU site and the hydraulic connectivity between the sedimentary cover and the granite aquifers. Our results suggest that two main mechanisms are responsible for the observed changes in groundwater pressure: (1) crustal dilation induced by the Tohoku earthquake causing a groundwater recharge from the sedimentary aquifers to the Toki granite aquifer where the sedimentary cover is thick; and (2) permeability increase along faults critically oriented for shear reactivation and oriented in the direction of the passing seismic wave. In this case, the seismic wave increases the shear stress acting on the fault promoting slip and a change in permeability through a mechanism of slip-induced dilation. Faults not critically stressed and faults critically oriented for shear reactivation but oriented perpendicular to the passing seismic wave are not reactivated.

地震波通过对断层稳定性的评估——以2011年日本中部东北地震引起的地下水位变化为例
在这项研究中,我们分析了2011年太平洋沿岸东北地震(Mw 9.0)引起的水南地下研究实验室(MIU)及其周围的几个钻孔所观测到的地下水压力变化。该项目的目的是通过数值分析来评估系统断层活动的方法的发展。为了达到这一目标,我们研究了地震波通过时该地区存在的断裂带的行为。建立了MIU场址的简化水文地质模型,并利用TOUGH2流动数值程序进行了一系列流体流动模拟。我们研究了研究区内三条断层(筑吉断层、日吉断层和主井断层)的渗透率变化对井段监测的地下水位的影响。我们还测试了MIU站点的凹陷锥的影响以及沉积盖层与花岗岩含水层之间的水力连通性。研究结果表明,地下水压力变化的机制主要有两种:(1)东北地震引起的地壳扩张导致地下水从沉积含水层向沉积覆盖较厚的Toki花岗岩含水层补给;(2)渗透率沿断层沿剪切再激活的临界方向和地震波通过方向增加。在这种情况下,地震波通过滑移诱发扩张机制,增加作用在断层上的剪应力,促进断层滑动和渗透率的变化。不具有临界应力的断层和面向剪切再激活但垂直于地震波的断层不会再激活。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Hydrology X
Journal of Hydrology X Environmental Science-Water Science and Technology
CiteScore
7.00
自引率
2.50%
发文量
20
审稿时长
25 weeks
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