We collected all of the well-water level data and bore-hole volume strain data with step-like changes induced by the 2008 Wenchuan Earthquake, and then compared the two kinds of data simultaneously obtained from one-well and obtained from two monitoring network, based on earth tide standardization within poro-elastic theory. The results are as follows: a) from the one-well data, the amplitude of standardized well water level is closely related to the standardized bore hole volume strain, the correlated coefficient is more than 98%; b) from the monitoring network data, the standardized amplitude of well water level changes is in the same order with the standardized amplitude of bore-hole volume strain changes. We inferred that the well water level can be as an approach to measure earthquake induced volume strain changes on site under the frame of poro-elasticity.
Seismic induced strain/stress changes are useful for evaluating the risk of following earthquakes after a large earthquake occurred. While measuring the strain/stress changes on site is not easy and cheap. Scientists keep trying to find approaches. Decades years ago scientists declaimed that confined wellaquifer system can be considered as strain meter according to the observation of water level oscillation changes induced by seismic waves and earth tide based on poroelastic theory (Blanchard and Byerly, 1935; Bovarson, 1970; Kano, 2005). Poro-elastic theory gives the relationship between water level and the volume strain changes. That suggests that we can get volume strain changes from well water level. While according to the water level steps induced by earthquakes, the results are controversial because some cases of the steps in a well kept decreasing or increasing regardless the compression or extension static stress/strain changes simulated from different earthquakes based on dislocation model (Wakita, 1975; Roeloffs, 1998; Matsumoto, 2002; Brodsky, 2002).
