Study on the Relationship between Water Level in Fengxiang Well,Regional Stress Field Change and Seismic Activity in Shaanxi
The northern section of the Longxian-Baoji fault zone has a strong degree of loc-king,but the locking degree of its southern section is less studied.The observation well of a confined aquifer is considered a sensitive"volumetric strain gauge",and the rise or fall of the well water level often reflects the state of regional stress in tension or compression.Fengxiang Well in Shaanxi is located in the central and southern section of the Longxian-Baoji Fault.Based on the analysis of the variation trend of the water level in Fengxiang Well from 2013 to 2023,the porosity of the aquifer,the volume compression coefficient of the solid skeleton,and the volume compression coefficient of the water were calculated for the aquifer of the well,under un-drained conditions,by using sliding fits such as the baro-metric pressure coefficient and the M2-wave tidal factor.The temporal characteristics of the tectonic stress field around the well were quantitatively analyzed by using the relation-ship between the water level variation of the well and the vertical stress variation of the aq-uifer.Based on the GNSS baseline and surface strain variation characteristics within the region,as well as the seismic activity characteristics since 2013,a comprehensive analysis suggests that the stress field variation characteristics in the region can be divided into two stages:① From 2013 to 2017,the water level of Fengxiang well decreased,and the verti-cal stress weakened,showing a tensile environment with low seismic frequency.② From 2017 to 2023,the water level of Fengxiang well tended to stabilize,and the vertical stress fluctuated around zero.The tension weakened and gradually transformed into a stage of stress accumulation and enhancement,with a significant increase in the number of earth-quakes.Based on the analysis of the water level,vertical stress,GNSS baseline and sur-face strain,as well as seismic activity characteristics in the Fengxiang well over the past decade,it can be concluded that the central and southern sections of the Longxian Baoji fault zone is in a relatively stable state with weak stress accumlation and small deforma-tion.
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