右江断裂带晚更新世活动的若干地质地貌证据及位移速率
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摘要
右江断裂带地处桂西断块区,有记载以来沿带曾发生40～50级地震15次,属中强地震带。笔者在室内卫片、航片、大比例尺地形图解译和分析的基础上,经野外实地调查,获得了断裂带晚更新世活动的若干地质地貌证据,实测了断裂的左旋位移数据。文中介绍了有关证据,并根据年龄数据,计算了断裂中、晚更新世以来的水平和垂直位移速率。断裂带在平面上分3大段,即百色以西段、百色—思林段、思林—坛洛段,各大段又可进一步分为若干个小段。断裂断错了距今(328±025)×104a～(1016±079)×104a的阶地堆积物和残坡积物,控制着百色—田东晚第四纪盆地的发育,地貌上形成断层谷和槽地、断层崖和陡坎,横穿断裂的水系发生同步左旋位移,其活动性质以左旋走滑为主,兼有张性差异运动。晚更新世不同时段以来断裂的水平位移速率为147～198mm/a,中更新世以来的垂直位移速率为074～076mm/a,晚更新世以来为01～035mm/a。该断裂的位移速率明显低于其西的川滇断块内部断裂,更低于川滇断块周边断裂。
The Youjiang Fault zone is located in the Guixi (Western Guangxi) fault block region. Since the beginning of seismic records, 22 earthquakes of magnitude 4.0～6 occurred in this region, among which the largest one is the magnitude 61/2 earthquake occurred in the area between Leye, Guangxi Autonomous Region and Luodian, Guizhou Province in 1875. Of these events, 15 earthquakes of magnitude 4.0～5.0 occurred on the Youjiang Fault zone. The Tianlin Bagui M 5.0 earthquake of 1962 and the Pingguo M 5 0 earthquake of 1977 had caused certain damages of basic installations in the regions. Obviously, the Guixi region is an active region of moderate earthquake, and the Youjiang Fault zone is an active belt of moderate earthquake, which plays an important role in the seismicity in Guixi fault block region and in the territory of the Guangxi Autonomous Region. Based on the interpretation and analysis of satellite images, aerophotos, and large scale topographic maps, as well as field investigation, a line of geologic geomorphic evidence of late Pleistocene activity of the Youjiang Fault zone have been obtained, and the left lateral displacements on the fault zone have been measured. This paper presents all these results and provides the horizontal and vertical slip rates of the fault zone since mid late Pleistocene. The Youjiang Fault zone can be divided into 3 segments. They are the west of Bose, Bose Silin and Silin Tanluo segments, each of which can be subdivided into several sub segments. The offset of late Pleistocene terrace deposit and talus can be observed along each segment of the fault zone. The ages of the deposits have been dated to be (3.28±0.25)×10 4 a BP～(10.16±0.79)×10 4 a BP. Geomorphically, the fault zone controlled the development of the Bose Tiandong late Quaternary basin. A series of fault valleys, troughs, and scarps were developed along the fault strand, while the drainage system crossing the fault zone was left laterally offset. According to the comparison of the amplitudes of vertical and horizontal displacements on the fault zone, it is inferred that the activity since late Pleistocene of the fault zone has been dominated by left lateral strike slipping accompanied by extensional differential motion. The horizontal displacement rate since late Pleistocene on the fault zone has been determined to be 1.47～1.98 mm/a, the vertical displacement rate since middle Pleistocene is 0.74～0.76 mm/a, and the vertical displacement rate since late Pleistoce is 0.1～0.35mm/a. All these values are significantly lower than those on the fault zones surrounding or within the Chuandian fault block. The recent results of GPS observation support also this conclusion.
The Youjiang Fault zone is located in the Guixi (Western Guangxi) fault block region. Since the beginning of seismic records, 22 earthquakes of magnitude 4.0～6 occurred in this region, among which the largest one is the magnitude 61/2 earthquake occurred in the area between Leye, Guangxi Autonomous Region and Luodian, Guizhou Province in 1875. Of these events, 15 earthquakes of magnitude 4.0～5.0 occurred on the Youjiang Fault zone. The Tianlin Bagui M 5.0 earthquake of 1962 and the Pingguo M 5 0 earthquake of 1977 had caused certain damages of basic installations in the regions. Obviously, the Guixi region is an active region of moderate earthquake, and the Youjiang Fault zone is an active belt of moderate earthquake, which plays an important role in the seismicity in Guixi fault block region and in the territory of the Guangxi Autonomous Region. Based on the interpretation and analysis of satellite images, aerophotos, and large scale topographic maps, as well as field investigation, a line of geologic geomorphic evidence of late Pleistocene activity of the Youjiang Fault zone have been obtained, and the left lateral displacements on the fault zone have been measured. This paper presents all these results and provides the horizontal and vertical slip rates of the fault zone since mid late Pleistocene. The Youjiang Fault zone can be divided into 3 segments. They are the west of Bose, Bose Silin and Silin Tanluo segments, each of which can be subdivided into several sub segments. The offset of late Pleistocene terrace deposit and talus can be observed along each segment of the fault zone. The ages of the deposits have been dated to be (3.28±0.25)×10 4 a BP～(10.16±0.79)×10 4 a BP. Geomorphically, the fault zone controlled the development of the Bose Tiandong late Quaternary basin. A series of fault valleys, troughs, and scarps were developed along the fault strand, while the drainage system crossing the fault zone was left laterally offset. According to the comparison of the amplitudes of vertical and horizontal displacements on the fault zone, it is inferred that the activity since late Pleistocene of the fault zone has been dominated by left lateral strike slipping accompanied by extensional differential motion. The horizontal displacement rate since late Pleistocene on the fault zone has been determined to be 1.47～1.98 mm/a, the vertical displacement rate since middle Pleistocene is 0.74～0.76 mm/a, and the vertical displacement rate since late Pleistoce is 0.1～0.35mm/a. All these values are significantly lower than those on the fault zones surrounding or within the Chuandian fault block. The recent results of GPS observation support also this conclusion.
引文
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DENGYe quan.1986.SpacedistributionandorientationofgeneticfaultsofthestrongearthquakeinGuangxi[J].SouthChinaSeismologicalJournal,6(1):26—32(inChinese).
广西壮族自治区地质矿产局.1985.广西壮族自治区区域地质志[Z].北京:地质出版社.
BureauofGeologyandMineralResourcesofGuangxiZhuangAutonomousRegion.1985.RegionalGeologyofGuangxiZhuangAutonomousRegion[Z].GelogicalPublishingHouse,Beijing(inChinese).
广西壮族自治区地方志编纂委员会编.1990.广西通志(地震志)[Z].桂林:广西人民出版社.
CompilationCommitteeofLocalChronicles,GuangxiZhuangAutonomousRegion.1990.AnnalsoftheGuangxiZhuangAu tonomousRegion(SeismicChronicles)[Z].GuangxiPeople’sPublishingHouse,Guilin(inChinese).
李天,杜其方,游泽李,等.1997.鲜水河断裂带及强震危险性评估[M].成都:成都地图出版社.
LITian shao,DUQi fang,YOUZe li,etal.1997.TheXianshuiheFaultZoneandtheAssessmentofSeismicRisk[M].CartographicPublishingHouseofChengdu,Chengdu(inChinese).
李伟琦.1989.广西新构造分区特征及其与地震的关系[J].华南地震,9(4):22—26.
LIWei qi.1989.TherelationshipbetweenthecharacteristicsofneotectonicregionalizationandearthquakesinGuangxi[J].SouthChinaSeismologicalJournal,9(4):22—26(inChinese).
李载沃.1992.百色盆地油气控制因素和勘探前景分析[J].广西石油地质与勘探,(1):1—12.
LIZai wo.1992.Controllingfactorsandexplorationprospectingofoil gasinBoseBasin[J].PetroleumGeologyandExplo rationinGuangxiProvince,(1):1—12(inChinese).
刘锡大,侯建军,游象照.1987.右江断裂带的新构造活动[J].地震研究,10(2):175—183.
LIUXi da,HOUJian jun,YOUXiang zhao.1987.NeotectonicmotionofYoujiangFaultzone[J].JournalofSeismologicalResearch,10(2):175—183(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.TheXiaojiangActiveFaultZone[M].SeismologicalPress,Beijing(inChinese).
吴时平,龙安明,尹克坚.1987.广西地震活动性研究[J].华南地震,7(1):48—62.
WUShi ping,LONGAn ming,YINKe jian.1987.AstudyonseismicactivityinGuangxi[J].SouthChinaSeismologicalJournal,7(1):48—62(inChinese).
向宏发,徐锡伟,虢顺民,等.2002.丽江-小金河断裂第四纪以来的左旋逆推运动及其构造地质意义:陆内活动地块横向构造的屏蔽作用[J].地震地质,24(2):188—198.
XIANGHong fa,XUXi wei,GUOShun min,etal.2002.SinistralthrustingalongtheLijiangXiaojinheFaultsinceQua ternaryanditsgeologic tectonicsignificance[J].SeismologyandGeology,24(2):188—198(inChinese).
尹克坚.1995.广西地区的水系展布与活动断裂及新构造应力场的关系[J].华南地震,15(1):62—67.
YINKe jian.1995.RelationsofriversystemwithactivefaultsandneotectonicstressfieldinGuangxiarea[J].SouthChinaSeismologicalJournal,15(1):62—67(inChinese).
张培震,王琪,马宗晋.2002.中国大陆现今构造运动的GPS速度场与活动地块[J].地学前缘,9(2):430—441.
ZHANGPei zhen,WANGQi,MAZong jin.2002.GPSvelocityfieldandactivecrustaldeformationinandaroundtheQing haiTibetPlateau[J].EarthScienceFrontiers,9(2):430—441(inChinese).
张培震,邓起东,张国民,等.2003.中国大陆的强震活动与活动地块[J].中国科学(D辑),33(增刊):12—20.
ZHANGPei zhen,DENGQi dong,ZHANGGuo min,etal.2003.Activetectonicblocksandstrongearthquakesinconti nentalChina[J].ScienceinChina(SerD),33(Suppl):12—20(inChinese).
WANGQi,ZHANGPeizhen,FreymuellerJT ,etal.2001.Present daycrustaldeformationinChinaconstrainedbyGlobalPositioningSystemmeasurements[J].Science,294:574—577.
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