The Research On Relationship Between Seismic Strain And Oscillation Of Groundwater In Wells-Aquifer System

Earthquakes are the results of rocks' stress-strain accumulation and release in the crustal movement. The change process of crustal strain is the most direct factors of seismic activity. As the most active components of the Earth's crust, the groundwater is universal, liquidity and difficult compression. Wells-aquifer system equivalent to a high sensitivity Volume strain gauge in closed good confined aquifer. Groundwater micro dynamic change, is the clue to understand underground stress state, current tectonic movement and seismic activity, is also the important information to explore earthquake precursors.North China block is the strongest earthquake activity area, is also the key area for earthquake monitoring. Ms6.2 earthquake occurred on January 10, 1998, 11 50 points in ZhangbeiXian, Hebei province. The earthquake occurred in the area which seismic activity level is not high in history and current, is a strong earthquake in weak region. Throughout the zhangbei Ms6.2 quake research history, research on the regional caused by earthquake, and relationship between strain and groundwater level anomalies is still less.This paper collected 11 wells observation data of groundwater level on the hour in the North China region. Using polynomial fitting method and digital filtering method to process the observation data, and extract tidal components of water level. We can compute tides factor through the harmonic analysis, and inversion calculate aquifer Volume strain according to the relationship between groundwater level and aquifer Volume strain. Then we will simulate Seismic strain field within the region using dislocation model, calculate the strain value in the earth's crust, and comparative analysis the simulated results and the computational result.The results showed that groundwater tidal effect mainly comes from the influence of M2 wave. Along fault zones different direction, changes of strain orders of magnitude show bigger difference. The strain is four quadrant distribution in the area, strain in tensile area is one order of magnitude larger than strain in compressive area. Strain value calculated by using the two methods can be consistent with each other, it shows that the method is feasible inversion calculating aquifer volume strain according to groundwater tidal effect, and calculation result have credibility.