四川西部理塘—巴塘地区的活动断裂与1989年巴塘6.7级震群发震构造研究
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摘要
四川西部的理塘—巴塘地区以近SN向的断裂构造为主,并发育 1组NNE和NW向的共轭剪切破裂带。文中在详细的TM卫片和航空照片判译的基础上,以活动构造地貌学为主线,重点解析了该地区断裂构造晚更新世—全新世以来活动的表现形式,确定近SN向的金沙江断裂带晚第四纪以来的近EW向的缩短速率为 2~3mm/a,NNE向巴塘断裂的右旋水平滑动平均速率为1. 3~2. 7mm/a,NW向理塘断裂的左旋水平滑动平均速率为 2 .6~4. 4mm/a。结合地球物理场、震源机制解、GPS测量等资料,分析了该地区现今地壳运动的总体态势及其所导致的块体运移规律,指出 1989年巴塘 6 .7级震群的成因,是由于NNE向巴塘断裂和NW向理塘断裂共轭剪切所派生的近EW向正断层的张性破裂所致,揭示了一个挤压构造环境内正断层发震的典型震例。
The Litang-Batang region of western Sichuan Province is located at the eastern section of the Tibet Plateau. Since the Late-Cenozoic, the East Tibet Block has thrust over the Sichuan-Yunnan Block from west to east along the NS-trending Jinshajiang Fault zone, resulting in the nappe tectonic belt of 30 km width accompanied by the formation of the NNE-trending Batang Fault and the NW-trending Litang Fault, a pair of conjugate shear faults. In the vicinity of Daoxu, south of Derenduo, the generally NS-trending Jinshajiang Fault zone extends along NNW direction and displaces left-laterally a series of gullies for about 120～140m. At south of Yarigong, the fault extends along NNE direction and dislocates right-laterally a series of gullies for about 180～210m. In contrast, no evidence of horizontal displacement is observed on the NS-trending segment of the fault. It is suggested, therefore, that the Jinshajiang Fault zone should be characterized by shortening in nearly EW direction. Based on the results of GPS measurement, the shortening rate is determined to be about 2～3mm/yr. The NW-trending Litang Fault is dominated mainly by left-lateral shear movement. According to the dislocation value and the initiation time of dislocation obtained at southeast of Kangga, southeast of Litang and northwest of Heni etc, the average horizontal slip rate on the Litang Fault is estimated to be 3.2～4.4mm/yr on the Litang-Dewu segment, and 2.6～3.0mm/yr on the segment to the north of Litang. The NNE-trending Batang Fault cuts obliquely the main part of the Jinshajiang tectonic zone, displaying mainly right-lateral shear movement. At Mangling Village of Markam County, Tibet, the average horizontal slip rate on the fault is estimated as 2.0～2.7mm/yr, wiile in the vicinity of Batang it is estimated to be 1.3～1.9mm/yr. The connecting line of the eqicenters of the 1989 Batang M6.7 earthquake swarm and the long-axis of the aftershock distribution all extend nearly along EW direction, and the focal mechanism solution indicates an EW-trending normal faulting. Therefore, we tend to believe that the NNE-trending Batang Fault and the NW-trending Litang Fault to be a pair of conjugate shear ruptures. The southern block between these two faults slips southwards, resulting in EW-trending normal fault at the intersection of the two faults. It was the tensile rupturing on the normal fault that induced the Batang M6.7 earthquake swarm, as evidenced by the development of EW-trending normal faults on the southern edge of the Maoya basin and the nearly EW-trending surface rupture of about 2 km in length produced by the Batang M6.7 earthquake swarm.
The Litang-Batang region of western Sichuan Province is located at the eastern section of the Tibet Plateau. Since the Late-Cenozoic, the East Tibet Block has thrust over the Sichuan-Yunnan Block from west to east along the NS-trending Jinshajiang Fault zone, resulting in the nappe tectonic belt of 30 km width accompanied by the formation of the NNE-trending Batang Fault and the NW-trending Litang Fault, a pair of conjugate shear faults. In the vicinity of Daoxu, south of Derenduo, the generally NS-trending Jinshajiang Fault zone extends along NNW direction and displaces left-laterally a series of gullies for about 120～140m. At south of Yarigong, the fault extends along NNE direction and dislocates right-laterally a series of gullies for about 180～210m. In contrast, no evidence of horizontal displacement is observed on the NS-trending segment of the fault. It is suggested, therefore, that the Jinshajiang Fault zone should be characterized by shortening in nearly EW direction. Based on the results of GPS measurement, the shortening rate is determined to be about 2～3mm/yr. The NW-trending Litang Fault is dominated mainly by left-lateral shear movement. According to the dislocation value and the initiation time of dislocation obtained at southeast of Kangga, southeast of Litang and northwest of Heni etc, the average horizontal slip rate on the Litang Fault is estimated to be 3.2～4.4mm/yr on the Litang-Dewu segment, and 2.6～3.0mm/yr on the segment to the north of Litang. The NNE-trending Batang Fault cuts obliquely the main part of the Jinshajiang tectonic zone, displaying mainly right-lateral shear movement. At Mangling Village of Markam County, Tibet, the average horizontal slip rate on the fault is estimated as 2.0～2.7mm/yr, wiile in the vicinity of Batang it is estimated to be 1.3～1.9mm/yr. The connecting line of the eqicenters of the 1989 Batang M6.7 earthquake swarm and the long-axis of the aftershock distribution all extend nearly along EW direction, and the focal mechanism solution indicates an EW-trending normal faulting. Therefore, we tend to believe that the NNE-trending Batang Fault and the NW-trending Litang Fault to be a pair of conjugate shear ruptures. The southern block between these two faults slips southwards, resulting in EW-trending normal fault at the intersection of the two faults. It was the tensile rupturing on the normal fault that induced the Batang M6.7 earthquake swarm, as evidenced by the development of EW-trending normal faults on the southern edge of the Maoya basin and the nearly EW-trending surface rupture of about 2 km in length produced by the Batang M6.7 earthquake swarm.
引文
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CHENGuo xing,ZHOURong jun,HUANGJin li, etal.2001.Tectonicdeformation, blockmovementandstrongruptureintheChuandianactivetectonicregionsincelateCenozoic[A].In:LUYan chou, etal(eds).Neotec tonicsandEnvironment.SeismologicalPress,Beijing(inChinese).
陈智梁,沈凤,刘宇平,等.1998.青藏高原东部地壳运动的GPS测量[J].中国地质,5:32—35.
CHENZhi liang,SHENFeng,LIUYu ping, etal.1998.GPSmeasurementofthecrustmovementintheeasternQinghaiTibetPlateau[J].ChinaGeology,5:32—35(inChinese).
程万正,陈天长.1994.1989年巴塘6.7级震群的复杂时-空扩展和震源力学机制[J].地震学报,16(2):153—159.
CHENGWan zheng,CHENTian chang.1994.Complextime spaceextensionandfocalmechanismoftheBatangM67seismicswarmin1989[J].ActaSeismologicaSinica,16(2):153—159(inChinese).
高原,吴忠良,周蕙兰.1998.四川地区1989年中强地震系列的震源破裂研究[J].地震学报,20(1):12—17.
GAOYuan,WUZong liang,ZHOUHui lan.1998.Epicenterrupturestudiesoftheseriesofmoderate strongearth quakeinSichuanregionin1989[J].ActaSeismologicaSinica,20(1):12—17(inChinese).
阚荣举.1977.我国西南地区现代构造应力场与现代构造运动特征探讨[J].地球物理学报,20(2):96—107.
KANRong ju.1977.ResearchonthemoderntectonicstressfieldandmovementinthesouthwesternregioninChina[J].ChineseJournalofGeophysics,20(2):96—107(inChinese).
李,汪良谋.1977.云南川西地区地震地质基本特征的探讨[A].见:国家地震局西南烈度队编.西南地区地震地质及烈度区划探讨.北京:地震出版社.
LIPing,WANGLiang mo.1977.Researchontheseismo gologicalcharacteristicsinYunnanWesternSichuanRegion[A].In:Seismo geologyandSeismicZoningintheSouthwestChina.SeismologicalPress,Beijing(inChi nese).
潘桂棠,王培生,徐耀荣,等.1990.青藏高原新生代构造演化[M].北京:地质出版社.
PANGui tang,WANGPei sheng,XUYao rong, etal.1990.CenozoicTectonicEvolutionoftheQinghaiTibetPlat eau[M].GeologicalPublishingHouse,Beijing(inChinese).
裴锡瑜.1985.利用重磁资料对四川西部地区地壳深部构造及其与地震关系的初步研究[J].四川地震,2:35—43.
PEIXi yu.1985.ResearchonthecruststructureandearthquakeinthewesternSichuanbythegravitymagneticdata[J].EarthquakeResearchinSichuan,2:35—43(inChinese).
宋方敏,汪一鹏,俞维贤,等.1998.小江活动断裂带[M].北京:地震出版社.
SONGFang min,WANGYi peng,YUWei xian, etal.1998.TheActiveXiaojiangFaultZone[M].SeismologicalPress,Beijing(inChinese).
沈军,汪一鹏,任金卫.2001.中国云南德钦-中甸-大具断裂带第四纪右旋走滑运动[A].见:马宗晋等主编.青藏高原岩石圈现今变动与动力学.北京:地震出版社.123—136.
SHENJun,WANGYi peng,RENJin wei.2001.TheQuaternaryright lateralstrike slippingontheDeqingZhongdi anDajuFaultzoneinYunan,China[A].In:MAZong jin, etal(eds).StudyonRecentDeformationandDy namicsoftheLithosphereofQinghaiXizhangPlateau.SeismologicalPress,Beijing.123—136(inChinese).
四川省地震局.1994.1989年四川巴塘强震群[M].北京:地震出版社.
SeismologicalBureauofSichuanProvince.1994.1989BatangStrongEarthquakeSwarminSichuanProvince[M].SeismologicalPress,Beijing(inChinese).
唐荣昌,韩渭宾主编.1993.四川活动断裂与地震[M].北京:地震出版社.
TANGRong chang,HANWei bin(eds).1993.ActiveFaultsandEarthquakesinSichuanProvince[M].Seismolog icalPress,Beijing(inChinese).
许志琴,侯立玮,王宗秀,等.1992.中国松潘-甘孜造山带的造山过程[M].北京:地质出版社.
XUZhi qin,HOULi wei,WANGZong xiu, etal.1992.OrogenicProcessesoftheSongpanGarzêOrogenicBeltofChina[M].GeologicalPublishingHouse,Beijing(inChinese).
ArmijoR,TapponnierP,HanT.1989.LateCenozoicright lateralstrike slipfaultinginsouthernTibet[J].JourGeophysRes,94(B3):2787—2838.
ChenC,BurchfielBC,LiuY, etal.2000.GlobalPositioningSystemmeasurementsforeasternTibetandtheirimpli cationsforIndia/Eurasiaintercontinentaldeformation[J].JourGeophysRes,105(B7):16:215—16,227.
HoltWE,NiJF,WallaceTC, etal.1991.TheactivetectonicsoftheeasternHimalayanSyntaxisandsurroundingregions[J].JourGeophysRes,96:14,595—14,632.
HoltWE,HainesAJ.1993.VelocityfieldsindeformingAsiafromtheinversionofearthquake releasedstrains[J].Tectonics,12:1—20.
RatschbacherL,FrischW,ChenC, etal.1996.Cenozoicdeformation, rotation, andstresspatternsineasternTibetandwesternSichuan,China[A].In:AnYin,HarrisionM (eds).TheTectonicEvolutionofAsia.CambridgeUnivPress.
WangE,BurchfielDC,RoydenLH, etal.1998.LateCenozoicXianshuiheXiaojiang,RedRiverandDaliFaultSystemsofSouthwesternSichuanandCentralYunnan,China[M].GeologicalSocietyofAmericaSpecialPaper,Boulder,Colorado.327.
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