HR: 0830h
AN: H31D-0497    [PDF]
TI: Temporal change in groundwater level following the 1999 Chi-Chi (Mw = 7.5) earthquake, Taiwan
AU: * Wang, C
EM: chiyuen@seismo.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720 United States
AU: Wang, C
EM: chwang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Nankang, TWN 11111 China
AU: Kuo, C
EM: chwang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Nankang, TWN 11111 China
AB: We analyze the post-seismic changes in the groundwater level after the 1999 Chi-Chi (Mw = 7.5) earthquake, Taiwan, as recorded by a network of 70 evenly distributed hydrological stations over a large alluvial fan near the epicenter of the earthquake. Two types of post-seismic responses may be distinguished: In type I, the groundwater level returned gradually towards the pre-seismic level. In type II, the post-seismic groundwater level remained nearly at the coseismic level or even departed further from the pre-seismic level for a period of time. In the type I post-seismic changes, two sub-groups may be identified: one with a characteristic time of ~105 s for wells located in deformed rocks near the ruptured Chelungpu fault, the other with a characteristic time of ~106 s for wells located in unconsolidated and undeformed sediments over the Choshui River fan. A model of subhorizontal aquifers with coseismic recharge and local discharge may explain the type I post-seismic changes. It predicts a characteristic length of 1500 - 5000 m for the confined aquifers, and of 150 - 500 m for the unconfined aquifers. Most type II post-seismic responses occurred along the coast and along the Peikang Stream, where the groundwater level is many meters below the surface water level. A model of sustained recharge of the aquifers from the surface water, due perhaps to enhanced vertical permeability from coseismic formation of fractures and cracks, may explain these type-II post-seismic changes. On the other hand, a model of sustained loss of groundwater, that outpaced the surface recharge, is needed to explain the continued lowering of groundwater level at the Liyu station near the ruptured Chelungpu fault.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
DE: 8105 Continental margins and sedimentary basins
SC: Hydrology [H]
MN: 2003 Fall Meeting