| The earthquake is defined as the stress-strain of rock accumulates and enhances unceasingly, when it surpasses the max bursting-strength of rock mass, it will burst suddenly, in diastrophism process. Observations and studies indicate that subsurface fluid precursor objectively exists. The confined water level precursor is most persuasive, because it can almostly reflect the change of crustal stress-strain, and the change can be quantitatively calculated. Although it has not been able to understand completely about each kind of the groundwater level's abnormal mechanism coming with seismic, but the earthquake prediction has potential social economy value, with the researching more deep and the recognizing level more progressive, using groundwater water level precursor to forecast earthquake is meaningful.The paper based on the analysis of influencing factors of groundwater level micro-dynamic and the characteristics of groundwater level micro-dynamic responding to stress , using the theory of water coupling with rock in rock mechanics, then established the model of the groundwater level responding to tide force and the model of the groundwater level responding to atmospheric pressure combine with tide force, and took the Luguhu Well, the Qionglai Chuan-22 Well and so on 6 observation wells for examples, Quantitatively studied the relationship of the groundwater level responding to tide force and responding to atmospheric pressure combine with tide force, have cleared about characteristics of groundwater level responding to non-tectonic stress factors such as tide force, atmospheric pressure and so on, have confirmed the rule of the groundwater level responding to non-tectonic stress in the period when there is no earthquake and without disturbance. These research-based, took the groundwater level of 8 observation wells on the North-South seismic belt as the object of study before the WenChuan Ms8.0 earthquake happened, qualitatively researched groundwater level dynamics change of single-well before the earthquake, identified anomalous characteristics of groundwater level before the earthquake. Through the research and preliminary understanded the anomaly characteristics and mechanism of the groundwater level change during the pre-earthquake, provided a basis for the utilization of groundwater level to predict earthquake.Achieved the following results:(1) The relationship of groundwater level micro-dynamic responding to tide force. Through studying the characteristics of groundwater level micro-dynamic responding to the tide force, combine with linear elastic theory, establish the model of the groundwater level responding to tide force, obtain the regression coefficient ( Bt z) of groundwater level change ( ?h )responding to the tide force change ( ?g z) which has physics significance. Quantitatively study the relationship of groundwater level responding to tide force in Luguhu Well among the 4 observation wells, the calculation results show that the 4 observation wells'groundwater level are close to the tide force, groundwater level change is mainly caused by the tide force during non-earthquake period.Divide the groundwater level responding tide force into two parts, first part is 3 days before lunation to 3 days after lunation, and second part is 3 days before half moon to 3 days after half moon. By analyzing two parts of the groundwater level of 4 wells including Luguhu Well, have the following conclusion, The related coefficient(R) of groundwater level responding to tide force in the first part is greater than the second part , It shows that groundwater level micro-dynamic of the first part is better responding to tide force than the second part. This conclusion doesn't mean distortion of the regression coefficient ( Bt z) of groundwater level responding to tide force. The cause of the conclusion is the groundwater level change a little following the little change of tide force in half moon and the precision of observation instrument is not accurate enough to record the little change of groundwater level. So when we use the regression coefficient ( Bt z) to decide the change of aquifer's characteristic, need to choose suitable time for analyzing.(2) The relationship of groundwater level micro-dynamic responding to atmospheric pressure combine with tide force.Through the analysis of groundwater level datum reveal that some of the observation wells'groundwater level micro-dynamic change following atmospheric pressure at the same time with the combined effect of the tidal force generally, the groundwater level responds to individual effects of tidal force or atmospheric pressure is not obvious, but the combined effect is significant, therefore, groundwater level observation wells for such study need to be considered both as a combination of factors. When the aquifer and overlying strata deform as linear elastic deformation, the atmospheric pressure and tide force change on the groundwater level can be considered as linear superposition, according to the combined effect of atmospheric pressure and tide force under the pore pressure equilibrium conditions inside and outside of wall, establish the model of groundwater level micro-dynamic responding to atmospheric pressure combine with tide force. Quantitatively study the relationship of groundwater level responding to atmospheric pressure combine with tide force in Qionglai Chuan-22 Well and Naxi Chuan-12 Well.Analyze the relationship of groundwater level responding to atmospheric pressure combine with tide force in Qionglai Chuan-22 Well by the model of the various time intervals average significance. The results show that, the regression coefficients of groundwater level responding to atmospheric pressure and tide force are increasing gradually with the increase of the time increment, and finally become constant, explain that the aquifer and wells have water exchange, and the exchange has completed in 30 minutes, when using hour datum to calculate, it can be ignored the value of the lag effect of groundwater level change in wells. Multiple correlation coefficient (R) is also increasing rapidly with the increase of the time increment, reflect that using the time interval mean value can effectively eliminate the observational error , this method can be used for the minute value of the observation wells'groundwater level datum pre-processing, eliminate the observation error effectively, improve the fitting precision.Analyze the relationship of groundwater level responding to atmospheric pressure combine with tide force in Nanxi Chuan-12 Well by the model. Obtain the result of groundwater level change responding to atmospheric pressure and vertical tide force is the duplicate correlation coefficient R=0.986, the regression coefficient of groundwater level responding to atmospheric pressure BP =-4.378, the regression coefficient of groundwater level responding to tide force Bt z=0.118. Explain that the Nanxi Chuan-12 Well's groundwater level is close to the synthesis response of atmospheric pressure and tide force, the groundwater level's variation is mainly caused by atmospheric pressure and tide force. (3) Identification of groundwater level anomaly of pre-earthquake.By analyzing the groundwater level of 8 wells on the North-South seismic belt before the WenChuan Earthquake happened, obtain the following conclusion:Firstly, have not found any long-medium-term or short-term anomalies in Luguhu Well, Nanxi Chuan-12 Well, Qionglai Chuan-22 Well and Jiangyou Chuan-10 Well, the long-medium-term anomaly of Jiangyou Chuan-10 Well need more information of its groundwater level any years before to judge.Secondly, there are anomalies in Beichuan Well, Deyang Chuan-08 Well, Pujiang Chuan-11 Well and Luzhou Chuan-13 Well. Beichuan Well shows short-term anomaly about 1 to 5 months before the WenChuan Earthquake happened and imminent anomaly in the month of the WenChuan Earthquake happened. Deyang Chuan-08 Well shows imminent anomaly in the month of the WenChuan Earthquake happened. Pujiang Chuan-11 Well shows medium-term anomaly about 6 to 12 months before the WenChuan Earthquake happened. Luzhou Chuan-13 Well shows medium-term anomaly about 1 to 6 months before the WenChuan Earthquake happened and imminent anomaly in the month of the WenChuan Earthquake happened.Each well shows different kind of anomaly, the anomalies have no rule; the developing process of anomalies is not synchronous and complicated with the time of earthquake happened. The earthquake-reflecting capacities of each well have to do with many factors such as the mechanical characters and hydrogeological parameters of aquifer media, the environment of groundwater storage, and so on.
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