河北赤城井水温对远场大震的响应特征研究

About the response feature of Chicheng wells’ temperature to the far-field large earthquakes in Hebei Province

在河北赤城井井下30 m、53 m、58 m处分别安装了3个温度传感器,进行水温微动态观测。通过对2004年12月以来全球发生的22次M_S≥8.0地震时赤城井不同深度水温观测数据的变化进行研究发现,井下30 m处水温均无明显同震变化;而7次大震时53 m、58 m处水温有明显的同震变化,53 m处水温同震初始变化形态均为上升,58 m处均为下降。同时,对水温变化机理进行探讨发现,井下30 m处水温日变幅度偏大是记录不到地震的主要原因;水温同震初始变化是由井孔水体对流引起的,53 m处水温同震初始变化形态均为上升是由于该处位于负温度梯度带,井孔中水体受震荡激发而加速对流与掺混是导致58 m处水温同震初始下降的主要原因,赤城井水温同震初始变化的后效恢复过程为热传导作用的结果。

Three temperature sensors were installed at depth of 30 m,53 m and 58 m underground wells for making microdynamic observations of water temperature in Chicheng well,Hebei Province.Based on the observation data of water temperature at different depths of Chicheng well and 22 times above M 8.0 earthquakes around the world since December 2004,we found that the water temperature at 30m underground performed no obvious co-seismic change,and the water temperature at 53 and 58 meters appeared obvious co-seismic changes in 7 times of great earthquakes,among which the initial change of water temperature was upward at the depth of 53 meter for the same earthquake,but the initial change of water temperature presented downward for the same earthquake at the depths of 58 meter.Meanwhile,when in the discussion of the mechanism of water temperature change,the main reason of the rising diurnal variation of water temperature did not record the earthquakes at the depth of 30 meters and the initial co-seismic change of water temperature is caused by the convection of the borehole water.In the depth of 53 meters the upward variation of initial changes of water temperature is located in the negative temperature gradient zone.Accelerated convection and mixing induced by oscillation in the water body of the well bore are the main reasons for the initial drop of water temperature at the depth of 58m due to co-seismic.The recovery process after initial co-seismic change of water temperature was caused by heat conduction in Chicheng well.