Groundwater Level Changes Induced by Teleseismic Earthquakes in Taiwan
Date Issued
2007
Date
2007
Author(s)
Lin, Keng-Yi
DOI
zh-TW
Abstract
Numerous mechanisms and models have been proposed to explain groundwater level fluctuations induced by distant earthquakes. Cooper et al. found that the responses of the groundwater level to earthquakes are frequency dependent and derived a solution for the amplification of the aquifer pore pressure due to the harmonic motion of the well water level. This study uses available seismic and monitor well data in Taiwan to analyze coseismic water level changes triggered by teleseismic surface waves. The water level data are obtained from six monitor wells: Hualien, Naba, Liujar, Tungwei, Chishan, Donher with sampling intervals of 1 second. Together with vertical ground velocities recorded at nearby BATS (the Broadband Array in Taiwan for Seismology) stations, the water level amplification is calculated based on the coherence between each seismogram and hydrograph of 44 distant earthquakes with magnitude M≧6.5 during the period from December, 2004 to June, 2006. For the events with M>7.0 and epicentral distances less than 5000 km, the seismically-induced water level fluctuations are clearly visible and the corresponding amplification values generally agree well with those predicted by the Cooper’s theory. The obtained best-fit values of transmissivity for six wells are similar, ranging from 1.26×10-5 to 3.16×10-5 m2/s. Furthermore, the threshold values of volumetric strains for the water level in response to seismic waves are estimated, and the sensibility of each well for monitoring oscillatory water level changes is inferred. The six wells are therefore classified into 4 classes: Donher and Chishan are the most sensitive and the earthquakes with strain > 10-9 are detectable; Naba is the next best (detectable for strain >10-8) ; Hualien and Tungwei are less sensitive (detectable for strain >10-7) and Liujar is imperceptible. These results can be used as references for further studies on monitoring earthquake induced groundwater level changes.
Subjects
地震
水位變化
水位振幅放大率
導水係數
體積應變
earthquake
water level changes
water level amplification
transmissivity
volumetric strains
Type
thesis
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