Research On Precursory Anomalies And Co-seismic Response Of Groundwater Associated With Wenchuan Earthquake

Water is widely distributing on the earth, just like the blood existing in thehuman body. Groundwater level will appear anomalous changes before and after anearthquake. Groundwater plays vital role in the forming of the earthquake.Researchers pay lots of attentions on the relationship between groundwater andearthquake.Taking Wenchuan earthquake as an example, groundwater exceptions in wellsare studied in this dissertation, then tidal analysis is done to get the tidal factor. So thechanging of tidal factor can be studied. After that, we studied the phenomena of cutoffflow in well QL based on the field survey. And the relationship between co-seismicwater-level changes and dislocation mode are also learned. Finally, we studied theco-seismic water-level changes in Three Gorges well-network. With these studies, weget the following conclusions:(1) 5 of the 16 wells in Sichuan province appeared long-term,middle-term orshort-term anomalous. The number of anomalies increased with the time approachingthe earthquake. These anomalies are mainly distributed along the Longmenshan andHuayingshan faults which have a strike of North-East. And it seems that theanomalies shift from the outside region into the source region, this phenomenon mayimport for the predicting of seismogenic time and the epicenter of the futureearthquakes.(2) Both M2and O1waves of the groundwater appear some anomalous before theearthquake. The number of anomalous wells increase with the time closer to theearthquake happenning. This phenomenon appears more clearly in O1wave. Thecharacteristic of spatial distribution is more complex than the anomalies in thegroundwater level.(3) The abnormal interruption of water flow in Qionglai well is an obviousmiddle-short anomalous which have an apparently mechanics basis. It was not causedby the drought or pumping nearly.(4) In the Sichuan region, the mechanic characteristic of strain inferred from theco-seismic water-level and strain inferred from the dislocation model are not allconsistent. 2/3 of them are same, and the rest are opposite with each other. The valueof strain inferred from the co-seismic water-level changes are one or two order biggerthan strain inferred form the dislocation model.(5) In the Three Gorges region, the strain get from the two methods are nearly inthe same order, but the characteristic of co-seismic water-level of the 8 wells are notsame. The response ability and characteristic are mainly determined by the location ofgeological condition, hydrogeology properties( such as transmissivity). What's more,the residual step changes in groundwater level may reflect the impact on the stressstate of the fault induced by the strong quake.