Study On The Relationship Between Dynamic Changes Of Groundwater And Seismic Activity

Groundwater possesses the characteristics such as wide distribution, good fluidity and incompressible. It can play as a ‘sensitive manometer’ with the capacity of amplifying the stress fluctuation when the well is located in a confined aquifer system. It has been documented by years of observations and researches that part of observation wells in the epicentral area will significantly behave changes before the strong earthquakes. The changes were found to be related to tectonic deformation of rocks in the earthquake-pregnant process, moreover, the dynamic changes on or around fault are likely to be the sensitive signals of tectonic deformation or earthquakes. There are many detailed records of groundwater precursors and many scientists did a large amount of researches on them. The sampling frequency is enhanced by the development of observation technology, and data with such sampling frequency contain a wealth of structure information. However, not all groundwater level anomalies are associated with tectonic deformation; they are also affected by groundwater extraction, artificial water injection and etc. These human activities can cause not only the changes of groundwater but also the increase of seismic activities.In this study, the relationship between groundwater dynamic changes and earthquake activities was thoroughly analyzed from several aspects, for example, coseismic responses of groundwater caused by far-field earthquakes, changes of groundwater in the earthquake-pregnant process, the injection-induced earthquakes and the drop of groundwater level caused by excessive extraction. The main content includes three aspects:1) Co-seismic response of water level in Changping well caused by Mw9.0 earthquake in Japan was analyzed, and the understanding of permeability enhanced caused by seismic wave were proved.2) Characteristics of underground fluid precursor during earthquake preparation process were systematically summarized, and based on digital observation data and the probability density distribution method, high frequency abnormal information in North South seismic belt before the Wenchuan Ms8.0 Earthquake were analyzed. The correlation between anomaly and seismogenic process were discussed by combining with the regional tectonic stress field.3) Seismic activity induced by injection in oil field and salt mine area were analyzed by using the fluid diffusion coefficient method, and the regional water level decline caused by geothermal exploitation were also discussed by using a three dimensional groundwater flow model.We put forward the right analytical tools and methods based on different circumstances, discussed the dynamic characteristics of groundwater caused by earthquakes and the distribution of injection-induced earthquakes. The research achievements could provide theoretical basis and analytical tools for practical needs on the study of such fields as following: formation mechanism of groundwater, the correlation between groundwater changes and tectonic stress, the fault rupture mechanism caused by groundwater, and etc.