Numerical Simulation Of Coseismic Response Of Huize Well Water Level To Ludian Earthquake

The coseismic static stress generated by the near-field earthquake will cause the change of the regional stress-strain field,which will increase the pore pressure in the compression zone and decrease the pore pressure in the expansion zone.The reflection in the well bore will cause the water level to rise or fall(Continuously increasing or decreasing),this is a fluid-solid coupling process.It was difficult to solve this process by analytical methods in the past.This article focuses on the coseismic response process of the Huize Well to the Ludian earthquake on August 3,2014,and establishes a coseismic rupture model and aquifer pores for the Ludian earthquake using Okada dislocation theory,porolinear elastic theory,and Navier-Stokes equations.The coseismic response model of pressure and the water level response model of the well-aquifer system under pressure disturbance are used for numerical simulation calculation using three models pseudo-coupling,aiming to reveal the whole process of the coseismic response of well water level to near-field earthquakes.This paper uses the three numerical models established in this paper to conduct a preliminary quantitative analysis of the strain field distribution,pore pressure evolution law and well water level change process caused by the Ludian earthquake.To a certain extent,it restores the difference between the water level of the Huize Well and the Ludian earthquake.Earthquake response process,objectively analyze the relationship between near-field seismic activity and groundwater level change,provide a reference for other near-field earthquake-induced well water level changes research,and also for the future exploration of more complex fluid-solid-thermal-chemistry Multiphysics coupling co-seismic well water level research lays the foundation.This article has achieved the following results:(1)The coseismic rupture model of the Ludian earthquake was established by using geological and seismic data,and the coseismic static strain field distribution generated by the Ludian earthquake was simulated.The strain field caused by the Ludian earthquake was distributed in four quadrants along both sides of the fault.The extreme points are distributed on both sides of the northern section of the fault.The maximum strain in the compression zone is-6.56×10-4,and the maximum strain in the expansion zone is 6.99×10-4.The strain field value decreases gradually away from the fault.(2)Derive a fluid-solid coupling control equation set with pore pressure and strain as variables,establish a coseismic response numerical model for the pore pressure of the target aquifer,and convert the strain field simulated by the coseismic rupture model into the pore pressure field distribution as the initial condition,To simulate the coseismic evolution process of pore pressure in Ludian area and Huize well.The simulation results show that the initial pore pressure distribution pattern caused by the Ludian earthquake is consistent with the strain field distribution,the extreme value of excess pore water pressure is 3.5×105Pa,and the extreme value of negative pressure is-3.73×105Pa.The perturbation value of pore pressure in the study area caused by the earthquake returns to the stable value before the earthquake within50 days,and the diffusion time of pore pressure is affected by the permeability coefficient and the three-dimensional water storage rate.When the size of the study area is constant,the greater the permeability coefficient,The faster the pore pressure spreads;the smaller the three-dimensional water storage rate,the faster the pore pressure spreads.The Ludian earthquake caused an instantaneous increase of 2900 Pa in the pore pressure of the Huize Well,and within 50 days,the pore pressure of the Huize Well returned to its initial state in the form of a power exponent.(3)Use Darcy’s law and Navier-Stokes equation to establish the water level response model of the downhole-aquifer system under pressure disturbance,and convert the disturbance value of the aquifer pore pressure caused by the earthquake into the value of water level change in the wellbore.The simulation results show that the water level of the Huize Well was affected by the earthquake instantaneously rose by 0.52 m,and returned to the pre-earthquake water level within 50 days.The change trend of the water level is similar to the measured water level,and both recover slowly after a step rise,but the simulated water level rise amplitude is larger than the measured value.The possible reasons are:(1)The established model is more ideal and does not consider the heterogeneity of the aquifer;(2)Under actual conditions,there are many wells in the study area to discharge pressure,but when the simulation is carried out in this article,there is only one well in the study area,which may cause the simulated rise water level to be too large;(3)The occurrence of well damage during the actual water level rise will cause the actual measured water level to be more than simulated The water level is low.