【摘要】 深井水温观测在中国已经开展了20年,但目前对于水温响应机理的研究还不充分。在对2004年12月26日印尼苏门答腊MS8.7地震后,中国地下流体观测井网中121个观测井水位、水温同震响应特征的研究中,作者发现了具有规律性的一类变化类型:当某些观测井水位出现振荡的时候,其同井水温绝大多数会出现几十分钟到数小时的下降—恢复过程。为了对此现象进行验证,又收集了河北唐山矿井2001年数字化以来39次远场大震水位、水温的同震响应资料,发现其具有相同的规律。在对可能造成水温下降的影响因素研究分析的基础上,提出了同震水温下降的气体脱逸模式,给出了在气泡脱逸过程中造成水温下降的2种主要影响因素,并利用此模式对部分观测现象进行了较合理的解释。更多还原

【Abstract】 The observation of water temperature in deep well has been carried out for more than 20 years in China.However,the study on the mechanism of water temperature co-seismic response is inadequate at present.On December 26,2004,the great earthquake of MS 8.7 occurred in the northwest offshore of Sumatra,Indonesia.After the shock,most of the observation wells in China recorded the coseismic response of water level and temperature.We studied the co-seismic response characteristics of water level and temperature in 121 wells and found the regular response characteristics.When the water level in a well oscillates,its water temperature will drop at the same time.The process will continue from dozens of minutes to several hours,and the process of the water temperature drop corresponds to the process of the water level oscillation.Once the water level oscillation stops,it restores to the level before the earthquake immediately.But,the water temperature rises at a slow speed and will take several hours to attain its former level.In order to confirm the observed phenomenon of co-seismic response of water level and temperature to one earthquake in multiple wells,we collected water level and temperature data for 39 far-field strong earthquakes in the Tangshankuang well in Hebei province.The same pattern was observed.For these 39 far-field strong earthquakes,the four factors,viz.the maximum amplitude ΔH(unit:m)of water level oscillation,the maximum water temperature drop ΔT(unit:℃),the earthquake magnitude M and the distance from epicenter D(unit:km),all satisfy the following three formulae by regression analysis.ΔT=0.009 9ΔH0.3842(1)lgΔH=2.232 9M-1.252 7lgD-7.920 5(2)lgΔT=0.857 9M-0.481 3lgD-7.658 3(3)Based on the analysis of the influencing factors that may cause the water temperature drop,the authors bring forward the gas escape mechanism for co-seismic water temperature drop.When the seismic waves reach the well,the aquifer undergoes periodic elastic deformation.Under the interaction of the periodic external force,surface tension and differential gas-fluid pressure,the gas at pore tips would create air bubble.At the same time,the gas dissolved in the ground water also can escape in the high-frequency oscillation process.During the process of bubble rise,its volume increases,absorbing heat,doing work outward,which cause the groundwater temperature dropping.Moreover the bubble escaped to external air will lose its own heat,which can cause the water temperature dropping as well.After the earthquakes,thermal convection will cause the temperature to recover because the water temperature nearby the sensor is below the water temperature of the observation aquifer.Based on such model and comparison of observation wells,in which the co-seismic water level oscillation but no noticeable drop in water temperature appeared,the authors found that the daily water temperature variation all surpassed 10-2℃,far more exceeding the daily water temperature variation of 10-3℃ of the wells in which noticeable co-seismic water temperature drop had been observed.Thus we can explain it in this way,larger daily water temperature variation would suggest that the observed aquifer is easy to be affected by the outside and has poor sealing.Therefore,the bore-hole is not the only gas escape channel and the gas can escape from many channels including above overburdens.Larger daily water temperature variation also conceals the temperature drop,leading to the fact that the drop of water temperature nearby the sensor is not obvious.We can optimize the water temperature observation system by adjusting the position of sensor.更多还原