Earthquake Research in ChinaVolume 25, Number 1, 2011Tidally Induced WaterTemperature Change inArtesian Wells'Ma Yuchuan' ,Liu Yaowei?) ,Ren Hongwei2) , and Sun Xiaolong21) China Earthquake Networks Center . China Earthquake Adninistration, Bejng 00045 ,China2) Institute of Crustal Dynamics , China Earthquake Administration，Beijing 100085 ,ChinaW ater temperature observation in wells , as a precursor observation project in China, aimsto capture stress-strain information during the preparation of earthquakes. The study ofthe water temperature tidal effct has important significance , for water temperature tidaleffect is both a reflection of stress-strain in crust and an interference factor of precursorobservations. With a view of thermal conditions in artesian wells , the paper holds that thereare two mechanisms for interpreting tidally induced water temperature changes in artesianwells. Namely, thermal conduction mechanisms and thermal convection mechanism. Thepaper then derives the quantitative relationship between water temperature and tidalvolumetric strain changes in an ideal artesian well. Finally, the water temperature tidaleffect in the Benxi artesian well is analyzed. The results show that the water temperaturetidal effect in Benxi well is the result of joint action of thermal conduction mechanism andthermal convection mechanism, in which thermal conduction mechanism plays a leadingrole.Key words: Artesian well; Water temperature; Earth tide; Thermal conduction ; Thermalconvection; Benxi areaINTRODUCTIONThe relationship between groundwater temperature micro-dynamic and crustal stress-strain oreven earthquakes has been an impotent scientifie issue for years. Groundwater temperature changespreceding earthquakes were reported in many studies ( Shimamura et al. , 1984; Fu Zizhong,1988; Mogi et al. ,1989; Che Yongtai et al. ,1996; Che Yongtai et al. ,2008). How the changesas earthquake precursors are confirmed is the key to solving the issue. Tidal effect has a closerelationship with crustal stress-strain, and is useful for earthquake precursor recognition. Studying中國煤化工Received on November 15, 2010; and revised on January:CCHCNMH Gjonsored by the“Subsurface Fluid Observational Specification Research Program"48Earthquake Research in Chinathe mechanisms of groundwater temperature tidal effct is meaningful because it helps usunderstand thermal condition changes and thermal transfer modes of certain ground areas understress loadings ( Cermak et al. ,2008 , 2009). It also provides better appreciation of how aquifersrespond to earth tides ( Rosaev et al. ,2003; Esipko et al. ,2007 ), and clarifies the ability ofgroundwater temperature responses to crustal stress-strains ( Furuya et al. ,1988 ;Kitagawa et al.，1996). As the groundwater temperature tidal effect is influenced by many factors , quantitativeanalysis on it is significant , thus becoming a research hotspot in recent years.From the mid-1980s , China started to construct groundwater temperature observation networksfor earthquake monitoring and prediction. There are currently hundreds of water temperatureobservation wells. According to existing data, we find that over 30 wells have obvious watertemperature tidal effects. These wells and their data lay the foundation for further study. We alsofind that water temperature is more sensitive to earth tides in artesian wells rather than in non-artesian ones. Based on the review of relevant studies of water temperature tidal effects in artesianwells , Furuya et al( 1988 ) and Zhang Zhaodong et al. (2002 ) believe that the effect relates withgroundwater flow changes caused by earth tides. Koizumi( 1990 ) analyzed the relationship betweengroundwater flow and temperature changes in an artesian well in Japan , and deduced theirquantitative relationship. Zhang Yongxian et al. ( 1991) obtained the same results in their study.However , the quantitative analysis of water temperature tidal effects in artesian wells is still rare inliterature. In this paper，we quantitatively analyze the mechanism of water temperature tidal effectsin artesian wells. We then use the results to interpret the water temperature tidal effect in theBenxi artesian well.1 THERMAL STATE IN ARTESIAN WELLSBefore analyzing the mechanisms of water temperature tidal effects in artesian wells , thethermal state in artesian wells need to be analyzed. The water in artesian wells outflow constantlyfrom discharge outlets and the wells have heat exchange with the outside environment from thewater surface. The thermal state in artesian wells may therefore be affected by many factors. Thefactors that influence long-term dynamics of water temperature include climate , rainfall, surfacewater infiltration, different aquifer water mixing and so on. The factors that influence micro-dynamics of artesian water may include three factors as follows:(1) When water outflows from an artesian well, there will be a temperature differencebetween the well water and surrounding rock , which arouses thermal conduction. The basic thermalconduction equation of well water and its surrounding rock is ( Che Yongtai et al. ,2008) ，aTa2r. a7g'T. g2T\(1)aar2rar r aφ0z'where T is the temperature,t is the time of thermal conduction,r is the radial distance from thewell wall to the outside in cylindrical coordinates,中 is the angle in cylindrical coordinates,k isthermal conductivity.(2) As temperature gradient and water movement exists in an artesian well, it will producethermal convection. It includes two cases. One is that the well water has heat exchange with theoutside environment , so the water in the well has different temperature to the water in the aquifer.The temperature gradient then exists in the horizontal direction , which is why thermal convectionoccurs when water moves between the well and the aquifer, The other, is that the well water hasheat exchange with the surrounding rock , with the te中國煤化工in the verticaldirection , and when water moves in the well , it will also!YHC N M H Gtion. The basicthermal convection equation in well-aquifer and in well'is (Che Yongtai et al. ,2008) ，Volume 25, Number 149三(v,pC,T) =ρC。af(2)axwhere x; is the migration distance of the water flow ,0; is the water velocity, ρ is the water density;C。is the heat capacity of water,T is the temperature and t is the time of thermal convection. .(3) If the temperature difference exists between the water and atmosphere at the watersurface of the well, there will be thermal diffusion. The impact of thermal diffusion is limited,usually no more than tens of meters. The basic thermal diffusion equation between the well waterand atmosphere is ( Che Yongtai et al. , 2008 ) ,q=a(T。-T.).(3)where q is the heat flux value,T. is the interface water temperature,T。is the interface atmospheretemperature ,a is the interface thermal diffusion coefficient.For an artesian well, the dynamics of water temperature at a certain depth has closerelationship with the condition of the aquifer, water temperature gradient , temperature probeposition and so on. Therefore, when analyzing the temperature-related phenomenon and itsmechanism in artesian wells, all factors need to be reasonably considered.2 TIDAL EFFECT ON WATER TEMPERATURE IN ARTESIAN WELLS2.1 Mechanisms of Tidal Effect on Water TemperatureAccording to the thermal state in artesian wells , we hold that there exists two mechanisms forinterpreting the tidal effect on water temperature.One is the thermal conduction mechanism. It can be interpreted as follows. Tidal volumestrain excites the pore pressure fluctuations in the aquifer. The fluctuations then drive the aquiferwater to flows between the aquifer and the well , which leads to the change of well water flow rate.In the process of water outflow from the well , because of thermal conduction between well waterand surrounding rock ，the well water temperature will change. The well water temperature changeis directly related with the changes of the well water flow. That is , if the well water temperature ishigher than the surrounding rock temperature, when well water flow becomes smaller, thesurrounding rock will receive more heat from the well water , and water temperature will reduce.When welll water flow becomes larger, the surrounding rock will draw less heat from the wellwater , and water temperature will rise. Tidal volume strain causes pore pressure fluctuation , thusleading to well water flow change. That is, the well water flow changes with the change of wellwater temperature.The other is the thermal convection mechanism. It can be interpreted as follows. Tidal volumestrain excites the pore pressure fluctuation in the aquifer. The fuctuations then force aquifer waterto flow between the aquifer and the well , making the flow velocity change. The change of velocitywill lead to thermal convection change both in the well-aquifer and in the well. The well watertemperature will change when thermal convection changes. The well water temperature change isdirectly related with the change of the flow velocity. That is,if well water temperature is higherthan the surrounding rock temperature, when flow velocity becomes smaller, thermal convectionwill become weaker in the well-aquifer and in the well , and water temperature will reduce. Whenflow velocity becomes lager, thermal convection will become stronger and water temperature willrise. Tidal volume strain causes fluctuation of pore pressu中國煤化工flow velocity.Flow velocity changes will cause well water temperatYHCNMHGe well walertemperature changes with the change of tidal volume strauuBoth of the mechanisms can explain the water temperature tidal effect in artesian wells.50Earthquake Research in ChinaConsidering the following reasons, only the thermal conduction mechanism is quantitativelyanalyzed in this paper. First , the thermal state is complex in artesian wells , and may be different atdifferent depths in a well. As the constitutive relation is relatively clear in the thermal conductionmechanism than that in thermal convection ，quantitative analysis on the thermal conductionmechanism is an effective method. Another reason is that we hold that thermal conduction may bedominant in some artesian wells with large water flow，which is unanimous with some researchers'studies ( Zhang Yongxian et al. , 1991; Koizumi,1990; Mogi et al. , 1989).2.2 Analysis of Thermal Conduction MechanismAssuming that tidal volumetric strain change causes pore pressure change ，then the pressurechange causes water flow change, and the water flow change induces water temperature change.The paper derives the quantitative relationship between the tidal volumetric strain change andwater temperature change in an ideal artesian well. The amount of water temperature change bythermal conduction mechanism can be obtained based on this.The paper adopts an ideal physical model of artesian well water temperature observation(Fig. 1) , with the assumptions that: ①groundwater micro-dynamic is relatively stable, and thegroundwater temperature in the recharging aquifer remains unchanged. The tide-inducedgroundwater discharge changes slowly, and the process is quasi-static; ②ground temperature isconstant in the horizontal direction and increases uniformly in the vertical direction; ③thechange of well water temperature with water flow is caused by thermal conduction of well waterwhen flowing through between well casing and surrounding rock; and ④the current in the wells issteady-state ideal fluid. Based on these assumptions , the quantitative relationship between the tidalvolumetric strain change and water temperature change can be derived as follows.Well mouthWater surfaceDischarge mouthGround surfaceWaterSurrounding rockTemperature probe十k .............Aquifer --777777777777777Fig. 1An ideal physical model of an artesign well中國煤化工。Volume strain change causes expansion and contrahus fluctuatingthe pore pressure of aquifer media. The pore pressureTYHCNMHGvolumestrainchange (As) can be expressed ( Bredehoeft,1967) as,Volume 25, Number 151OP =- EAe,(4)Where ,p is the density of water ,g is the acceleration due to gravity,S, is the specific storativity ofaquifer , the negative sign indicates the decrease of pore pressure with the expansion of the aquifermedium and the increase of pore pressure with the contraction of the aquifer medium.According to hydro-dynamic theory, the pore pressure at the top of the aquifer can beexpressed asP =pg(h +hg)+→pu'+ P.(5)where h is the distance between the water surface and the discharge outlet, and is also the waterlevel of artesian wells in the Chinese water level observation network. ho is the distance betweenthe centre line of the discharge outlet and the top of the aquifer; u is the flow velocity at thedischarge outlet ,and P。is the barometric pressure at the water surface.The water flow Q at the discharge outlet can be expressed asQ=Au(6)where A is the cross sectional area of the discharge outlet.Assuming the well water as steady-stale ideal fluid , the relationship between h and v is,(7)From equation(5) ~ (7)we get,P=ef +pgh。+P.(8)Assuming that the well water temperature change with flow rate is caused by heat conductionof well water when flowing between surrounding rock and the well casing , the relationship betweenwater temperature and water flow is ( Koizumi, 1990) ,T(z) =To-y+E(1-exp(-長2)(9)where z is the distance between the temperature probe and the top of the aquifer,T(z) is the watertemperature at depth z, T。is the temperature of the recharging aquifer, γ is the geothermal2πakgradient,Q1 is the well water flow,E=oa ,a is the internal radius of the well,h is the thermalpedconductivity of the well casing,c is the heat capacity of the groundwater, and d is the thickness ofthe well casing.In the artesian well (Fig. 1), the well water flow changes caused by tidal volume strainchanges consist of flow changes in the dischargie outlet and the water level changes Sh. The paperassumes that the water flow at the discharge outlet is equal to the well water flow when the wellwater flow is relatively large. From equation (4),(8) and (9), we can obtain the relationshipbetween AT and As in quasi-static process as follows ,γyA'g0T=-20.s6:(1-exp(-品。)0。(10)Where, Q。is the average value of the water flow at the discharge outlet. The first negative sign inthe right side of formula indicates that the water temperature decreases when the aquifer mediumexpands , and the water temperature increases when the中國煤化工Equation (10) shows that the ability of water tempYH.CNMH G; tides is mainlyrelated with the specific storativity of the aquifer , geotheumrau g auncit, wCl waiciflow , radius ofthe well and temperature probe position. In particular, the ability of the water temperature in52Earthquake Research in Chinaresponse to earth tides will be strong if the distance between the temperature probe and theobserving aquifer is great and the radius of the well is small.3 TIDAL EFFECT ON WATER TEMPPERATURE IN THE BENXI ANTESIAN WELLBased on the analysis in section 2 , the paper takes the Benxi artesian well as an example todiscuss the mechanisms of tidal effect on water temperature. First, based on the analysis of thethermal conduction mechanism, we compute the ratio of water temperature changes OT to tidalvolume strain changes Aε , using the Benxi well data. Then , another ratio of OT to△ε is gainedfrom the harmonic analysis of Benxi well's water temperature observation data. Finally, themechanisms of water temperature tidal effect are discussed after comparing the two results.The Benxi well locates in Taigou village ，Qiaotou town, Benxi city , Liaoning Province,P. R.China. The location is at 123. 70 degrees east and 41. 29 degrees north. The elevation of thewellhead is 173. 34m, and the depth of the well is 1213. 46m. The area where the Benxi welllocates is in the junction between the east extension of E-W trending Y inshan tectonic belt and thesecond giant uplift of the Neocathaysian , belonging to the Taizihe depression zone. The observingaquifer water of Benxi well is fissure confined water. The well has two aquifers , one at 600m , theother locales between 952m ~ 957m. When the water from the two aquifers mixes and flows to thedischarge outlet , the water temperature is abouto 20 (Sun Xiaolong , 2009 ). The well adopts theSZW-1 A digital thermometer to measure the temperature , and the temperature probe is placed 37mbelow the ground surface. The thermometer's resolution is≤0. 0001 C , the observation accuracy is≤0. 05C，the short-term stability is≤0. 0001 C/d , the long-term stability is I≤0. 001 C/a andthe sampling rate is 1 time/ min ( CEA ,2001).According to the power spectrum estimation，diurnal and semidiurnal periodic variations existin the water temperature data of the Benxi well ( Fig.2 (a), ( b)), showing signifcant tidaleffects on water temperature of the Benxi well. Besides , the dynamics of the water level is similarto water temperature , showing significant tidal effects too (Fig.2 (c),(d)).3.1 Analysis of Thermal Conduction Mechanisms in the Benxi WellUsing the analysis results of thermal conduction mechanisms in section 2, we compute theratio of water temperature changes AT to tidal volume strain changes Aε as:0T_yA'g(11)- 250(1-omp(-川Based on the Benxi well data , the parameter values in equation (11 ) are as follows: Thermalconductivity k=0.3J/(s●cm●9C), internal radius of the well a = 8. 9cm, density of waterρ=1.0g/cm'，heat capacity of the groundwaterc= 4. 2J/(g. C ) , thickness of the well casingd=0.3cm, then E =; 2πak= 13.31cm'/s. Taking the section of the Benxi well that is underpcdthe depth of 600m a8 a big aquifer, then z=5.63 x 10* cm. The measured water flow of theBenxi well is Q。= 150cm'/s, which meets the requirement of relatively large water flow.According to the values ofz,E and Qo,exp( -一z) in equation (11) is equal to zero, thenQoequation (11 )can be simplified as，AT=.γAg中國煤化工(12)Aε= - 2ESs0In equation (12) , only the specific storativity of aqMYHCNMHGequation (6)~ (9) , we can obtainVolume 25，Number 153(舊)19.7019.65 |信19.60-昌19.55102034056Timeld50(6)25 t27.78b| 22.73h13.16h11.76h°h8.26h 7.81h-500.050.100.150.200.30Frequency/h-'2.52.4(C).日2.030SOTime/d5((d27.8h22.73h258.26h7.81h差-250.10 -0.25Frequency/h-1Fig.2(a) Water temperature data in the Benxi artesian well from December 2007 toJanuary 2008. ( b) Power spectrum of the water temperature data. (c) Water leveldata in the Benxiartesian well from December 2007 to January 2008.(d) Power spectrum of the water level dataP=2pgh+ρgh。+P.(13)If the ocean tide is not considered and barometric pressure influence is corrected , the waterlevel change is only caused by earth tides. From equation (13) and (4) , we can obtainAP =- QEOε = 2pgQh(14)Ss中國煤化工andh,TYHCNMHGSs = 1/(2(15)54Earthquake Research in ChinaWhere,Oh is the variation of water level.Harmonic analysis of the Benxi well's water level observation data can get the ratio of Oh toAε in equation (15). In the method of harmonic analysis , the theoretical value is tidal volumestrain value ( magnitude is 10-9 ). The results of harmonic analysis then represent water levelchanges caused by the theoretical unit of tidal volume strain that is Oh/ A8.The paper chooses the water level integral point data of the Benxi well from November 2007to April 2008. Harmonic analysis of the data after barometric pressure correction shows that themain waves with large amplitude have high precision,such as 0, and K diurnal waves, M2 andS2 semidiurnal waves. We take the average value of the main waves to denote Oh/ As , then△h/As =4. 4789mm/10-9 ,and we have Sg=1/(2雪) =1.1163 x 10~9/cm.In equation ( 12), the values of other parameters are as follows : Temperature gradientγ=0.20mC/cm, where mC = 1/1000C , and temperature gradient was gained when the Benxiwell was constructed. Cross sectional area of the discharge outlet A = 4. 91cm’, and theacceleration due to gravity g = 980cm/s2.Based on the mentioned parameters above , we can obtain from equation (12)AT = 1. 0762mC/10°3.2 Harmoric Analysis of Water Temperature Data of Benxi WellWe can obtain another OT/Aε ration by harmonic analysis of the Benxi well watertemperature data.On the principles of smooth , continuous, and less interference, we choose the data of theBenxi well from November 2007 to April 2008 for the analysis ( Fig. 3). Some pretreatment wasapplied to the original data that is completing a small amount of missing data by interpolation,eliminating the sudden jump changes caused by calibration and adjusting equipment.100 r元-100 Fa)|昌-20010203045002-b){0.1--0.1-0.260.10e)0.050.00中國煤化工-0.05MHCNMHG-0.10 t6(Volume 25, Number 1d)|.5-.0 H-2.51023(40502.40(e2.352.302.25 I2.200204C6019.6819.6619.6419.6219.582(30， 1030(g1020E 10101000tlFig. 3Data of the Benxi artesian well from December 2007 to January 2008(a) Theoretical data of gravity earth tide; (b) Short-period water level data;(c) Short-period water temperature data; ( d) Short: period barometric pressure data;(e) Long-period water level data;( f) Long-period water temperature data ;(g) Long- period barometric pressure dataFirst, we choose the data of the Benxi well from November 2007 to April 2008 for theanalysis. The short-period and long-period changes are isolated from the water level, watertemperature and barometric pressure data using the Piel Zaitsev filtering method ( Zhang Guominet al. ,2001) ,The results are shown in Fig. 3. From Fig.3(a) ~(c) where water level and watertemperature have the same daily fluctuations as the theoretical gravity tidal values. From Fig. 3(e)~( g) , the long-period fluctuations of water temperature have similar morphology with that of thewater level, and the long-period fluctuations of water中國煤化工:1 have reversemorphology with that of barometric pressure. Based on tlmetric pressurechange affects water level change , and the water levelCNMHGntue Ceangrethus the barometric pressure change indirectly affects water temperature change. Hence before56Earthquake Research in Chinaharmonic analysis is carried out , the influence of barometric pressure change on water temperaturedynamics should be eliminated.The influence of changes of barometric pressure on water temperature can be eliminated withthe same method with that of water level ( Du Pinren, 1991) , namely,T(t) = T。(t) - BP.(t + Ot)(16) .where T。(t) is the original water temperature ,T(t) is the water temperature after barometric pressurecorrection ,B is the barometric pressure efficiency on water temperature,Ot is the lag time.The barometric pressure efficiency B in equation ( 16) denotes the effect of barometricpressure change on water temperature change , defined as,B =- dT/dP。(17)Using the Piel Zaitsev filtering method ，short-period and long-period changes are isolatedfrom water temperature and the barometric pressure data from November 2007 to April 2008 of theBenxi well. Using regression analysis, we can obtain the barometric pressure efficiency B a3.21 mC/hPa (The correlation coefficient is 0. 813 , greater than the level of significance test).The△t in equation ( 16) denotes the lag time that water temperature changes after barometric .pressure changes. The△l can be estimated by lag correlation analysis of the long-period pressureand water temperature changes. According to the data of the Benxi well from November 2007 toApril 2008 ,the lag time Ot equals 6 hours.Given the barometric pressure efficiency B and lag time Ot, the influence of barometricpressure change on water temperature can be eliminated basing on equation ( 16).，The paper chooses the water temperature integral point data of the Benxi well from November2007 to April 2008 for the harmonic analysis , using Venedikov's method. In the method，the theoreticalvalue is the tidal volume strain value ( magnitude is 10- ). Therefore ,he results by harmonic analysisrepresent the water temperature change induced by unit theoretical tidal volume strain，that is△T/Qs.The harmonic analysis of the data after barometric pressure correction is shown in Table 1.From the harmonic analysis , we know that:(1) Waves with large amplitude have high precision, such as 0, and K, in diumal waves andM2 and S2 in semidiurmal waves.(2) The water temperature of the Benxi well is sensitive to tidal strain and the average tidalfactor of 0, K, M2, and S2 waves can reach 1. 8240mC/10-9. Take the average to denoteOT/Aε , then we getAT_一= 1.8240mC/10-Table 1 Results of harmonic analysis of water temperature data in Benxi artesian wellTidal FactorPhase LagMaximum amplitudeNo.Partial Wave(mC/10~9)(°)(mC )Qr1. 8204 +0.1364-1.9029士4.34812. 9795士1. 09960，1. 8992 +0. 0257-4.5264 +0. 776914. 7021 +1. 0022.3720土0. 3763- 21.7575 +9. 63541. 3971土1.40391. 5056 +0.0192- 9.34922 +0. 749615. 1524 +0. 76742.1579 +0. 3176- 13. 6488土8. 67601. 4685士1.28841. 8215 +0. 4351- 14.0963士14. 52330. 7500 +0. 92672N2.2620 +0. 4401-8. 6529 +4. 57070. 6032 +0. 17261. 6911 +0. 04807. 07883土1.63873. 3720土0. 2507M21.8093土0.008610. 180| 中國煤化t0. 2543102. 2569 +0. 318719. 152:0.251112. 0817 +0.01598. 5410YHCNMHG+0.2357122. 6066土1. 2545- 22. 3464 +27.63280. 2698 +0. 9003Volume 25, Number 15'OT/ Os equals to 1. 0762mC/ 10 -9 computed by equation ( 16) , while it equals 1. 8240 mC/10 : 9by harmonic analysis of water temperature data. Both results show that in the aspect of themagnitude , the thermal mechanism is the main mechanism of water temperature tidal effects in theBenxi well. However, the magnitude computed equation ( 16) is less than that by harmonicanalysis. The difference can be interpreted as the contribution of the thermal convectionmechanism. The tidal effect on water temperature in the Benxi well is therefore the result of jointaction of both thermal conduction mechanisms and thermal convection mechanisms, in which thethermal conduction mechanism is dominant.4 SUMMARY AND DISCUSSIONThe following conclusions are drawn after analyzing the tidal effect on water temperature inthe Benxi artesian well.(1) Tidal effects on water temperature in an artesian well is a real response of local aquifersto stress-strain. Its mechanisms include thermal conduction and the thermal convectionmechanisms. The result of harmonic analysis of water temperature data after barometric pressurecorrection can reflect tidal influence on well water temperature.(2) In the thermal convection mechanism of water temperature tidal effects in artesian wells,the ability of water temperature in response to earth tides relate mainly to the specific storativity ofhe aquifer, geothermal gradient, well water flow, radius of the well and temperature probeposition.(3) For some artesian wells with large water flow , the tidal effect on water temperature is theresult of both the thermal conduction mechanism and the thermal convection mechanism , in whichThese conclusions are preliminary. In-depth study is needed to investigate the tidal effect onwater temperature in artesian wells, such as, quantitative analysis of thermal convectionmechanisms and phase lag. In addition, the water temperature tidal effect in non-artesian wells iscommon and only by systematically studying the mechanisms of these efects in non-artesian wells，we can thoroughly understand the mechanisms of water temperature tidal effects in wells.The authors gratefully acknowledge Che Yongtai , Wang Haiyan and Tang Jiu'an for their kindhelp and support.The paper was published in Chinese in the journal of Earthquake Research in China ( ChineseEdition)，Volume 26 , Number 2 ,2010.REFERENCES .Bredehoeft J D. Response of well-aquifer systems to earth tides [J]. Journal of Geophysical Research, 1967,72(12) :3075 ~ 3087.Cermak V, Bodri L, Safanda J. Tidal modulation of temperature oseillations monitored in borehole Yaxcopoil-1( Yucatan, Mexico) [J]. Earth and Planetary Science Lelters ,2009 ,282 :131 ~ 139.Cermak V ,Saianda J, Bodri L. Precise temperature monitoring in boreholes: evidence for oscillatory convection?Part I: Experiments and field data [J]. Int. J. 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Earthquake ,2002 ,24(2) :208 ~214 ( in Chinese with English abstract).About the AuthorMa Yuchuan ，born in 1985 , graduated from the Institute of Crustal Dynamics, CEA, worksin the Department of Earthquake Prediction of CENC. His major interests include earthquakeforecast and the study on the relationship between subsurface fuids and earthquakes. E-mail:mayuchuan07@ 126. com.中國煤化工MYHCNMHG