Monitoring of subsurface fluid(underground fluid)is an important part of efforts for earthquake prediction in China.The nationwide network,which monitors groundwater level,water temperature,and radon and mercury in groundwater,has been constructed in the last decades.Large amounts of abnormal fluid changes before and after major earthquakes have been recorded,providing precious data for research in earthquake sciences.Many studies have been done in earthquake fluid hydrogeology in order to probe the nature of the earthquake.Much progress in earthquake fluid hydrogeology has been made in the last decades.The paper provides a review of the advances in research on earthquake fluid hydrogeology over the last40 years in China.It deals with the following five aspects:(1)an introduction to the development history of monitoring networks construction;(2)cases of different subsurface fluid changes recorded before some majorearthquakes which occurred in the last decades;(3)characteristics of subsurface fluid changes following major earthquakes;(4)mechanism of subsurface fluid changes before and following earthquakes;(5)application of earthquake fluids in the hydrogeology field.
Changes in barometric pressure can affect the micro-dynamic state of groundwater level.The groundwater level data carry a lot of important information of tectonic activity and earthquakes.It is very significant to eliminate the barometric pressure effects from the groundwater level data in order to recognize seismic anomalies effectively.With the analysis of the main influential constituents of barometric pressure and their changes,we can have a better understanding of the changes of the aquifer medium,which can provide useful information for earthquake prediction.Taking the May 12,2008 Wenchuan earthquake as an example,this paper deals with the influence of barometric pressure on groundwater level based on observational data from Nanxi,Qionglai and Chaohu wells.The methods of the linear regression and the deconvolution regression were employed to remove the barometric pressure from the groundwater level data.The harmonic analysis and the spectral analysis were used to recognize the main influential waves of barometric pressure effect.A comparison was conducted on the main influential waves before and after the earthquake.The results showed that the main influential waves of barometric pressure effect changed and the amplitudes of all constituents also changed.This phenomenon may result from the characteristics of the influential constituents of pressure,or from the changes of the aquifer medium,which were caused by the earthquake.
