5.12汶川地震后龙门山断裂带东北段现今地应力测量结果分析
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摘要
5.12汶川大地震发生后,在龙门山断裂带东北段,开展了6个钻孔的原地应力测量工作.测量钻孔分别位于龙门山中央断裂带上下两盘的平武、北川、江油和广元等地.钻孔孔深在200～500m之间,共取得了72个测试段的地应力测量数据,以及其中33个测段的印模定向试验数据,由此获得了每个测点处地应力的赋存状态,包括地应力量值随孔深的变化以及地应力作用方向.根据库仑准则,结合Byerlee定律对各测点实测数据进行分析,可以看出,龙门山断裂带上盘现今地应力的作用强度高于下盘.其上、下两盘现今地应力赋存状态特征及其差异性显示出该区域处于不均衡的应力环境,容易导致断裂失稳而产生新的活动;印模定向试验数据表明,龙门山断裂带东北段的北川、江油、平武的最大水平主应力优势方向为NEE向;广元附近为NWW或近东西方向.结合已有的研究成果,初步得到龙门山断裂带现今地应力作用方向的分段性特征,即大致以北川为界,龙门山断裂带东北段应力方向显示了与西南段不同的特征.其西南段现今地应力的优势作用方向为北西方向,而龙门山断裂带东北段,自江油、北川、平武一带至广元、青川附近,其现今地应力的最大水平主压应力的优势作用方向呈现了NEE→NWW的赋存状态和变化趋势.本文获得的研究结果对于认识5.12汶川特大地震的动力学机制具有一定的借鉴和启示作用.
In-situ stress measurements in 6 boreholes at the northeastern section of the Longmenshan fault zone were carried out after the 5.12 Wenchuan earthquake.The test boreholes,of which the depth is between 200~500 m,were at Pingwu,Beichuan,Jiangyou and Guangyuan areas,located at the hanging wall and foot wall of the Longmenshan central fault,respectively.Totally 72 depth interval test data for stress magnitudes and 33 depth interval data for directions of the maximum horizontal principal stress were obtained.According to the Coulomb faulting criterion,combined with the Byerlee law,analysis on the in-situ stress state for each test point was carried out,indicating that the stress value at the hanging wall is much higher than that of the foot wall,implying that the fault activity is apt to be triggered.The impression packer test results show that the dominant direction of the maximum horizontal principal stress at Beichuan,Jiangyou and Pingwu is NEE,and at Guangyuan is NWW or east-west direction.Compared with the previous study results of the Longmenshan area,the current stress field zoning characteristis regarding the stress direction were obtained,i.e.,the dominant stresss direction of the north east section of the Longmenshan fault zone is different from that of the south west part.The dominant direction of current stress of the south west part is NW.In the north east part,from Jiangyou,Beichuan and Pingwu to Guangyuan and Qingchuan,the direction of the current stress changes from NEE to NWW.The results of this paper may be helpful for the study of the dynamic mechanism of the 5.12 Wenchuan earthquake.
In-situ stress measurements in 6 boreholes at the northeastern section of the Longmenshan fault zone were carried out after the 5.12 Wenchuan earthquake.The test boreholes,of which the depth is between 200~500 m,were at Pingwu,Beichuan,Jiangyou and Guangyuan areas,located at the hanging wall and foot wall of the Longmenshan central fault,respectively.Totally 72 depth interval test data for stress magnitudes and 33 depth interval data for directions of the maximum horizontal principal stress were obtained.According to the Coulomb faulting criterion,combined with the Byerlee law,analysis on the in-situ stress state for each test point was carried out,indicating that the stress value at the hanging wall is much higher than that of the foot wall,implying that the fault activity is apt to be triggered.The impression packer test results show that the dominant direction of the maximum horizontal principal stress at Beichuan,Jiangyou and Pingwu is NEE,and at Guangyuan is NWW or east-west direction.Compared with the previous study results of the Longmenshan area,the current stress field zoning characteristis regarding the stress direction were obtained,i.e.,the dominant stresss direction of the north east section of the Longmenshan fault zone is different from that of the south west part.The dominant direction of current stress of the south west part is NW.In the north east part,from Jiangyou,Beichuan and Pingwu to Guangyuan and Qingchuan,the direction of the current stress changes from NEE to NWW.The results of this paper may be helpful for the study of the dynamic mechanism of the 5.12 Wenchuan earthquake.
引文
[1]Wu M L,Zhang Y Q,Liao C T,et al.Preliminary results ofin-situ stress measurements along the Longmenshan faultzone after the Wenchuan Ms8.0earthquake.Acta GeologicaSinica,2009,83(4):746-753.
[2]郭啟良,王成虎,马洪生等.汶川Ms8.0级大震前后的水压致裂原地应力测量.地球物理学报,2009,52(5):1395-1401.Guo Q L,Wang C H,Ma H S,et al.In-situ hydro-fracturestress measurement before and after the Wenchuan Ms8.0earthquake of china.Chinese J.Geophys.(in Chinese),2009,52(5):1395-1401.
[3]唐荣昌,韩渭宾.四川活动断裂与地震.北京:地震出版社,1993.Tang R C,Han W B.Active faults and earthquakes inSichuan Province(in Chinese).Beijing:Seismological Press1993.
[4]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4):389-403.Deng Q D,Chen S F,Zhao X L.Tectonics,Scismisity anddynamics of Longmenshan mountains and its adjacentregions.Seismology and Geology(in Chinese),1994,16(4):389-403.
[5]陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3):657-673.Chen G G,Ji F J,Zhou R J,et al.Primary research ofactivity segmentation of Longmenshan fault zone since late-quaternary.Seismology and Geology(in Chinese),2007,29(3):657-673.
[6]Haimson B C,Cornet F H.ISRM Suggested Methods forrock stress estimation-Part 3:hydraulic fracturing(HF)and/or hydraulic testing of pre-existing fractures(HTPF).International Journal of Rock Mechanics&MiningSciences,2003,40(7-8):1011-1020.
[7]李方全,刘光勋.地应力测量、地壳上部应力状态与地震.中国地震,1986,2(1):50-55.Li F Q,Liu G X.Stress measurement,stress state of uppercrust and earthquake research.Earthquake Research in China(in Chinese),1986,2(1):50-55.
[8]Zoback M D,Tsukahara H,Hickman S.Stress measurementsin the vicinity of San Andreas fault:Implication for the magnitudeof shear stress at depth.J.Geophys.Res.,1985,11:6157-6173.
[9]Zoback M D,Healy J H.In situ stress measurements to 3.5km depth in the cajon pass scientific research borehole-implications for the mechanics of crustal faulting.J.Geophys.Res.,1992,97(B4):5039-5057.
[10]丰成君,陈群策,吴满路等.水压致裂应力测量数据分析—对瞬时关闭压力Ps的常用判读方法讨论.岩土力学,2012,33(7):2149-2159.Feng C J,Chen Q C,Wu M L,et al.Analysis of hydraulicfracturing stress measurement data-discussion of methodsfrequently used to determine instantaneous shut-in pressure.Rock and Soil Mechanics(in Chinese),2012,33(7):2149-2159.
[11]Byerlee J.Friction of rocks.Pure and Applied Geophysics,1978,116:615-626.
[12]张伯崇.孔隙压力、断层滑动准则和水库蓄水的影响//苏恺之,李方全,张伯崇等.长江三峡坝区地壳应力与孔隙水压力综合研究.北京:地震出版社,1996:166-198.Zhang B C.Pore pressure,fault slip criterion and influence ofresevoir impounding//Su K Z,Li F Q,Zhang B C,et al.Integrated research on the stress field and pore pressure atthe Three Gorges site(in Chinese).Beijing:SeismologicalPress,1996:166-198.
[13]张致伟,程万正,阮祥等.汶川8.0级地震前龙门山断裂带的地震活动性和构造应力场特征.地震学报,2009,31(2):117-127.Zhang Z W,Cheng W Z,Ruan X,et al.Seismicity andtectonic stress of the Longmenshan fault zone before 2008Wenchuan Ms8.0earthquake.Acta Seismologica Sinica(inChinese),2009,31(2):117-127.
[14]谢富仁,崔效锋,赵建涛等.中国大陆及邻区现代构造应力场分区.地球物理学报,2004,47(4):654-662.Xie F R,Cui X F,Zhao J T,et al.Regional division of therecent tectonic stress field in China and adjacent areas.Chinese J.Geophys.(in Chinese),2004,47(4):654-662.
[15]刘健,熊探宇,赵越等.龙门山活动断裂带运动学特征及其构造意义.吉林大学学报(地球科学版),2012,(录用待刊).Liu J,Xiong T Y,Zhao Y,et al.Kinematic characteristics ofLongmenshan active fault zone and its tectonic implication.Journal of Jilin University(Earth Science Edition),2012,(in press).
[16]崔效锋,谢富仁,张红艳.川滇地区现代构造应力场分区及动力学意义.地震学报,2006,28(5):451-461.Cui X F,Xie F R,Zhang H Y.Recent tectonic stress fieldzoning in Sichuan-Yunnan region and its dynamic interest.Acta Seismologica Sinica(in Chinese),2006,28(5):451-461.
[2]郭啟良,王成虎,马洪生等.汶川Ms8.0级大震前后的水压致裂原地应力测量.地球物理学报,2009,52(5):1395-1401.Guo Q L,Wang C H,Ma H S,et al.In-situ hydro-fracturestress measurement before and after the Wenchuan Ms8.0earthquake of china.Chinese J.Geophys.(in Chinese),2009,52(5):1395-1401.
[3]唐荣昌,韩渭宾.四川活动断裂与地震.北京:地震出版社,1993.Tang R C,Han W B.Active faults and earthquakes inSichuan Province(in Chinese).Beijing:Seismological Press1993.
[4]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4):389-403.Deng Q D,Chen S F,Zhao X L.Tectonics,Scismisity anddynamics of Longmenshan mountains and its adjacentregions.Seismology and Geology(in Chinese),1994,16(4):389-403.
[5]陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3):657-673.Chen G G,Ji F J,Zhou R J,et al.Primary research ofactivity segmentation of Longmenshan fault zone since late-quaternary.Seismology and Geology(in Chinese),2007,29(3):657-673.
[6]Haimson B C,Cornet F H.ISRM Suggested Methods forrock stress estimation-Part 3:hydraulic fracturing(HF)and/or hydraulic testing of pre-existing fractures(HTPF).International Journal of Rock Mechanics&MiningSciences,2003,40(7-8):1011-1020.
[7]李方全,刘光勋.地应力测量、地壳上部应力状态与地震.中国地震,1986,2(1):50-55.Li F Q,Liu G X.Stress measurement,stress state of uppercrust and earthquake research.Earthquake Research in China(in Chinese),1986,2(1):50-55.
[8]Zoback M D,Tsukahara H,Hickman S.Stress measurementsin the vicinity of San Andreas fault:Implication for the magnitudeof shear stress at depth.J.Geophys.Res.,1985,11:6157-6173.
[9]Zoback M D,Healy J H.In situ stress measurements to 3.5km depth in the cajon pass scientific research borehole-implications for the mechanics of crustal faulting.J.Geophys.Res.,1992,97(B4):5039-5057.
[10]丰成君,陈群策,吴满路等.水压致裂应力测量数据分析—对瞬时关闭压力Ps的常用判读方法讨论.岩土力学,2012,33(7):2149-2159.Feng C J,Chen Q C,Wu M L,et al.Analysis of hydraulicfracturing stress measurement data-discussion of methodsfrequently used to determine instantaneous shut-in pressure.Rock and Soil Mechanics(in Chinese),2012,33(7):2149-2159.
[11]Byerlee J.Friction of rocks.Pure and Applied Geophysics,1978,116:615-626.
[12]张伯崇.孔隙压力、断层滑动准则和水库蓄水的影响//苏恺之,李方全,张伯崇等.长江三峡坝区地壳应力与孔隙水压力综合研究.北京:地震出版社,1996:166-198.Zhang B C.Pore pressure,fault slip criterion and influence ofresevoir impounding//Su K Z,Li F Q,Zhang B C,et al.Integrated research on the stress field and pore pressure atthe Three Gorges site(in Chinese).Beijing:SeismologicalPress,1996:166-198.
[13]张致伟,程万正,阮祥等.汶川8.0级地震前龙门山断裂带的地震活动性和构造应力场特征.地震学报,2009,31(2):117-127.Zhang Z W,Cheng W Z,Ruan X,et al.Seismicity andtectonic stress of the Longmenshan fault zone before 2008Wenchuan Ms8.0earthquake.Acta Seismologica Sinica(inChinese),2009,31(2):117-127.
[14]谢富仁,崔效锋,赵建涛等.中国大陆及邻区现代构造应力场分区.地球物理学报,2004,47(4):654-662.Xie F R,Cui X F,Zhao J T,et al.Regional division of therecent tectonic stress field in China and adjacent areas.Chinese J.Geophys.(in Chinese),2004,47(4):654-662.
[15]刘健,熊探宇,赵越等.龙门山活动断裂带运动学特征及其构造意义.吉林大学学报(地球科学版),2012,(录用待刊).Liu J,Xiong T Y,Zhao Y,et al.Kinematic characteristics ofLongmenshan active fault zone and its tectonic implication.Journal of Jilin University(Earth Science Edition),2012,(in press).
[16]崔效锋,谢富仁,张红艳.川滇地区现代构造应力场分区及动力学意义.地震学报,2006,28(5):451-461.Cui X F,Xie F R,Zhang H Y.Recent tectonic stress fieldzoning in Sichuan-Yunnan region and its dynamic interest.Acta Seismologica Sinica(in Chinese),2006,28(5):451-461.
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