汶川大地震“远端效应”——龙泉驿地热异常成因探讨
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摘要
应用遥感地质解译、土壤氡气测量、地温测量以及地电测试等技术方法,结合现场勘查和相关地质资料,对成都市龙泉驿点状地热异常现象的成因机制进行探讨。龙泉驿断层被南北向和北东-南西向的次级断层切割,断层遥感影像清晰。断层上方土壤中出现极高的氡气浓度异常,从旁侧向地热异常点逐渐升高,显示断层的活动性和良好的渗透性,沿断层有流体上升。断层上方近地表局部填充的块状疏松土壤起到"导热管"的作用。发震于龙门山逆冲推覆造山带的汶川大地震及其余震的剧烈运动,使成都前陆盆地中的岩块沿中三叠统下部滑脱层滑动,产生大量构造热。热流沿滑脱层向远端的前陆隆起——龙泉山传递,通过龙泉驿断层向上溢流,并经"导热管"在地表形成点状地热异常。龙泉驿地热异常的主导因素是汶川大地震引发的构造热产生的地震地热异常"远端效应"。龙泉山断裂带不可能发生较大的破坏性地震。该地区可能有丰富的地热资源,值得进一步研究。
By use of the geologic remote sensing,soil radon measurement,geoelectric survey,ground temperature measurement,in combination with the related geologic information and site survey,this paper studies the mechanism of "spotted geothermal anomaly" in Longquanyi of Chengdu.The Longquanyi fault cut by its secondary faults has trends of N-S and NE-SW.These faults have a clear remote sensing image.The concentration of the soil radon above the faults is very high,moreover,from the exterior to the spotted geothermal anomaly,the concentration of the soil radon heightens gradually.All the evidences indicate that the Longquanyi fault has activities and high permeability and some fluid can rise through this fault.The loose soils locally distributed over the fault work as a "heat pipe".The Wenchuan earthquake was triggered by the Longmenshan overthrust nappy belt.Vigorous movements of the Wenchuan earthquake caused the rocks of the Chengdu foreland basin to dislocate along with the Middle Triassic lower slip horizon and generated a great quantity of structural heat,then the heat transferred along the slip horizon to the Longquanshan Mountain —— the uplift foreland of the Longmenshan nappy structural belts.Finally,the heat could rise through the active Longquanyi fault and come into being spotted geothermal anomaly on the surface with the help of the "heat pipe".The main cause of the geothermal anomalies maybe the earthquake "endpoint effect" of structural heat triggered by the Wenchuan earthquake.No destructive earthquake will happen in Longquanshan,and there will be a good exploration prospect of geotherm.Longmenshan is worth further researching.
By use of the geologic remote sensing,soil radon measurement,geoelectric survey,ground temperature measurement,in combination with the related geologic information and site survey,this paper studies the mechanism of "spotted geothermal anomaly" in Longquanyi of Chengdu.The Longquanyi fault cut by its secondary faults has trends of N-S and NE-SW.These faults have a clear remote sensing image.The concentration of the soil radon above the faults is very high,moreover,from the exterior to the spotted geothermal anomaly,the concentration of the soil radon heightens gradually.All the evidences indicate that the Longquanyi fault has activities and high permeability and some fluid can rise through this fault.The loose soils locally distributed over the fault work as a "heat pipe".The Wenchuan earthquake was triggered by the Longmenshan overthrust nappy belt.Vigorous movements of the Wenchuan earthquake caused the rocks of the Chengdu foreland basin to dislocate along with the Middle Triassic lower slip horizon and generated a great quantity of structural heat,then the heat transferred along the slip horizon to the Longquanshan Mountain —— the uplift foreland of the Longmenshan nappy structural belts.Finally,the heat could rise through the active Longquanyi fault and come into being spotted geothermal anomaly on the surface with the help of the "heat pipe".The main cause of the geothermal anomalies maybe the earthquake "endpoint effect" of structural heat triggered by the Wenchuan earthquake.No destructive earthquake will happen in Longquanshan,and there will be a good exploration prospect of geotherm.Longmenshan is worth further researching.
引文
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[3]邹谨敞,邵顺妹.活动断裂的遥感影像研究[J].环境遥感,1995,10(3):182-187.
[4]杨金中,聂洪峰,李景华.遥感技术在浙江东部穿山半岛地区活动断裂调查中的应用[J].国土资源遥感,2003,(4):50-53.
[5]郑文俊,郭华,袁道阳,等.遥感影像信息在活动断裂研究中的应用[J].高原地震,2002,14(2):15-20.
[6]孟广魁,何开明,班铁,等.氡、汞测量用于断裂活动性和分段的研究[J].中国地震,1997,13(1):43-50.
[7]任明甫.利用断层气(土气氡)探测琼北地区的断裂活动性[J].华南地震,2000,20(1):66-70.
[8]张炜,王吉昌,鄂秀满,等.水文地球化学预报地震的原理和方法[M].北京:教育科学出版社,1988.
[9]郝建国,潘怀文,毛国敏,等.准静电场异常与地震———一种可靠短临地震前兆信息探索[J].地震地磁观测与研究,2008,21(4):10-17.
[10]夏邦栋.普通地质学[M].北京:地质出版社,1995.
[11]王春林.华南地区温泉地震和活动性断裂的研究[J].华南地震,1982,2(4):9-15.
[12]徐纪人,赵志新,石川有三.青藏高原中南部岩石圈扩张应力场与羊八井地热异常形成机制[J].地球物理学报,2005,48(4):863-868.
[13]孙爱群,牛树银.地幔热柱演化及其地热效应———华北地热异常的深部构造背景[J].地球学报,2000,21(2):182-188.
[14]刘树根,罗志立,赵锡奎,等.龙门山造山带-川西前陆盆地系统形成的动力学模型及模拟研究[J].石油试验地质,2003,25(5):432-438.
[15]陈社发,邓起东,赵小麟,等.龙门山中段推覆构造带及相关构造的演化和形变机制[J].地震地质,1994,16(4):404-420.
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