Studies on Mechanisms of Coseismic Sustained Groundwater-level Changes
Date Issued
2010
Date
2010
Author(s)
Wang, Pei-Ling
Abstract
Base on high sampling rate records of three monitoring wells in Taiwan, we analyze the relation between coseismic water-level change and earthquake magnitude, hypocentral distance and distribution, and compare the calculated volumetric strain change with observed coseismic water-level change, in order to discuss possible mechanisms to sustained water-level change. Between 2004 and 2009, the Hualien, Zhuagnwei-2 and Chishan-3 wells recorded 280, 97, 47 oscillatory water-level changes, and 18, 25, 5 sustained water-level changes, respectively. Those earthquakes, which caused sustained water-level change, were located near the Hualien well. While the Zhuangwei-2 well recorded earthquakes as far as the 2008 Wenchuan earthquake 1935 km away from the well. And the Chishan-3 well recorded earthquakes located in the southern and eastern Taiwan. Geology and structure as well as hypocentral distance and earthquake magnitude affect coseismic water-level changes. There are earthquakes that induced large water level oscillations with no sustained water-level change, but some earthquakes induced small water level oscillations with induced sustained water-level change. To the Hualien, Zhuangwei-2 and Chishan-3 wells, the square correlation coefficient between sustained water-level change and oscillation range are 0.51, 0.53 and 0.48, respectively. Therefore, seismic shaking may not account for sustained water-level change. Liquefaction can account for coseismic rises. However, only 17% of sustained water-level changes at the Hualien well, 16% at the Zhuangwei-2 well, and 0% at the Chishan-3 well showed coseismic rises. Enhanced permeability may not account for the coseismic changes in the three wells, because it can’t apply to the Hualien and Zhuangwei-2 well that recorded coseismic rises and falls, and the different rates in sustained water-level changes at the Chishan-3 well. Static strain change can account for 83% of coseismic changes at the Hualien well, 60% at the Zhuangwei-2 well, and 80% at the Chishan-3 well. The inconsistency between calculated strains and observations could be caused by different physical properties of aquifers and the complexity of stress redistribution. Therefore, coseismic sustained water-level changes at the three wells may due to static strain changes, but a simple dislocation model may be insufficient to predict pore pressure change at a specific site.
Subjects
groundwater
coseismic
sustained change
the Hualien well
the Zhuangwei well
the Chishan well
Type
thesis
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