Advances in research on earthquake fluids hydrogeology in China:a review

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 last 40 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 major earthquakes 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.

Coseismic effects recorded by Fujian subsurface fluid network and its meaning to earthquake prediction

Based on analyses of the spatio-temporal evolutionary characteristics of teleseismic response recorded by Fujian subsurface fluid network and in combination with earthquakes happened in Fujian province during the same period, this paper points out that the step-like rising of water level after distant earthquakes may include some regional stress field information, and the area where water level step-like rises could be the position that the stress concentrated on and where the future earthquakes would occur. If combined with other impending precursors, the location of the events may be predicted to a certain degree.

Numerical simulation of spatial-temporal evolution characteristics of subsurface fluid based on strong body seismogenic model$$$$

Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we Studied the char acteristics of 'field precursors' and 'focus precursors' of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ② dilatancy emerges and anomalyfocus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③ anomalies spreed continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large scale dilatancy.

The subsurface fluid anomaly field and its genesis of Zhangbei-Shangyi earthquake

The paper presents a brief account of typical subsurface fluid anomalies of Zhangbei-Shangyi earthquake before itsoccurrence on January 10 of 1998. Based on which the fundamental characteristics of the anomaly field and itsformation and evolution are analyzed and discussed. The research results show that the middle-long, middle andshort term anomaly fields were mainly dominated by the structure activities, and the imminent and earihquaketime anomaly fields were controlled by the earthquake source. Therefore, the authors put forward that the way ofscientific search for earthquake prediction should probably be adjusted to the monitoring and grasping of fieldregime from the tracing process of sources, and realize the limited prediction.