青海玉树地区活动断裂与地震

青海玉树是巴颜喀拉地块西南边界上的典型历史强震区。最新的活动断裂遥感解译与地表调查结果表明,该区新构造期间主要发育清水河断裂带、玉树断裂带、阿布多断裂带和杂多断裂带4条NW向左旋走滑活动断裂带。其中,构成玉树—鲜水河—小江断裂系尾端构造的玉树活动断裂带是该区活动性最显著的岩石圈断裂。该断裂是由当江断裂、结古—结隆断裂和巴塘断裂3条斜接的主干断层和夹杂其间的多条次级断裂所共同构成的Z型左旋剪切张扭性变形带。它在上新世以来和晚第四纪期间的左旋走滑速率为4.0~5.4mm/a,调节了该区大部分的块体挤出与旋转变形,并构成该区大震活动的主要控震构造。历史强震梳理和古地震研究揭示,玉树主干走滑断裂带自约14530a BP以来至少发生了包括2010年地震在内的共11次大地震,原地重复间隔平均在千年以上,最长达近3000a。1738年玉树西北地震之后,玉树—甘孜断裂带的主干断层表现为平均间隔为50~100a的低频、串联式分段破裂过程,并且大震活动存在从东南向西北迁移的趋势。通过对玉树断裂未来大地震危险性进行综合地质判定认为,该区至少仍存在6段未来百年内大地震危险程度不同的地震空区,潜在的大地震震级为Mw6.6~7.3,其中危险性相对较高的段落主要是当江断裂带的当江—拉则段和结古—结隆断裂带上的结隆—叶卡诺段与桑卡—相古段。     

青海玉树活动断裂带的多期古地震滑坡及其年龄

2010年青海玉树Ms 7.1级地震发生后,笔者在开展玉树灾区地震地质灾害调查中发现13处古地震滑坡遗迹。调查结果表明,玉树古地震滑坡主要集中分布在玉树活动断层两侧5km范围内,规模普遍较大,多具有多期活动特征,且与周围古地震相伴生,空间上体现出发震断层对其发育的控制作用。同时,古地震滑坡地形地貌、沉积特征、年代学特征等方面的证据表明,其常具有原地复发的特征。据古地震滑坡堆积体的AMS 14C测年结果,认为目前发现的典型古地震滑坡主要发生在全新世中晚期,并集中分布在5个时期,与古地震探槽揭示的古地震事件期次及发生年代具有较好的对应关系。进一步对比古滑坡规模和分布范围,发现玉树断裂带在全新世中晚期发生2次规模较大的古地震滑坡事件,与地震探槽揭示的古地震特点相符。研究结果表明,群发性古地震滑坡是识别古地震事件的重要地貌标志,可从年代学上揭示古地震事件发生的具体时间,对于补充古地震事件资料和恢复古地震在时间与强度上的分布都具有重要意义。     

青海玉树活动断裂带的多期古地震滑坡及其年龄

2010年青海玉树Ms 7.1级地震发生后,笔者在开展玉树灾区地震地质灾害调查中发现13处古地震滑坡遗迹。调查结果表明,玉树古地震滑坡主要集中分布在玉树活动断层两侧5km范围内,规模普遍较大,多具有多期活动特征,且与周围古地震相伴生,空间上体现出发震断层对其发育的控制作用。同时,古地震滑坡地形地貌、沉积特征、年代学特征等方面的证据表明,其常具有原地复发的特征。据古地震滑坡堆积体的AMS14C测年结果,认为目前发现的典型古地震滑坡主要发生在全新世中晚期,并集中分布在5个时期,与古地震探槽揭示的古地震事件期次及发生年代具有较好的对应关系。进一步对比古滑坡规模和分布范围,发现玉树断裂带在全新世中晚期发生2次规模较大的古地震滑坡事件,与地震探槽揭示的古地震特点相符。研究结果表明,群发性古地震滑坡是识别古地震事件的重要地貌标志,可从年代学上揭示古地震事件发生的具体时间,对于补充古地震事件资料和恢复古地震在时间与强度上的分布都具有重要意义。     

青海玉树断裂带地震落石的地震地质意义

2010年青海玉树Ms 7.1级大地震引发了一系列次生地质灾害,其中地震落石是除地震滑坡外沿断裂带及其邻侧最常见的现象。对玉树震区落石的调查发现,该区多处存在非常典型的多期地震落石分布现象,指示该区地震落石的发育与其他古地震现象类似,具有多期性和一定的原地复发性。实地调查表明,该区地震落石分布的主要特征为：多集中发育在活动断裂带附近的陡峭基岩斜坡下方,分布零散,且滚动较远,并常与古地震滑坡相伴生。初步获得的8个地震落石钙膜U系测年结果分布在距今6030±300a BP、4720±210a BP、3530±490~3560±280a BP、2010±160a BP、1090±70a BP、760±20a BP和230±20a BP年龄段,与该区古地震探槽和滑坡反映的地震事件比较吻合,进一步揭示玉树断裂带附近在全新世中晚期发生过多期可导致地表产生地震落石的事件。同时也说明,地震落石及其钙膜测年是特别值得进一步探索的潜在古地震研究方法或途径。     

青海玉树断裂带地震落石的地震地质意义

2010年青海玉树Ms 7.1级大地震引发了一系列次生地质灾害,其中地震落石是除地震滑坡外沿断裂带及其邻侧最常见的现象。对玉树震区落石的调查发现,该区多处存在非常典型的多期地震落石分布现象,指示该区地震落石的发育与其他古地震现象类似,具有多期性和一定的原地复发性。实地调查表明,该区地震落石分布的主要特征为:多集中发育在活动断裂带附近的陡峭基岩斜坡下方,分布零散,且滚动较远,并常与古地震滑坡相伴生。初步获得的8个地震落石钙膜U系测年结果分布在距今6030±300a BP、4720±210a BP、3530±490~3560±280a BP、2010±160a BP、1090±70a BP、760±20a BP和230±20a BP年龄段,与该区古地震探槽和滑坡反映的地震事件比较吻合,进一步揭示玉树断裂带附近在全新世中晚期发生过多期可导致地表产生地震落石的事件。同时也说明,地震落石及其钙膜测年是特别值得进一步探索的潜在古地震研究方法或途径。     

玉树地震地表破裂特征及其破裂方式

北京时间2010年4月14日玉树Ms7.1级地震产生了长约50km的地表破裂带,地表破裂系统非常典型。本文通过对果庆益荣松多村附近河滩与结古镇西南河道两岸2个地表破裂点的野外观测和地表破裂的力学分析,探讨玉树地震地表破裂特征和方式。在果庆益荣松多村附近河滩地表破裂与地震陡坎呈间隔式左行右阶排列,具转换压缩性质;在结古镇西南河道北岸主地表破裂带中地表破裂非常发育,出露一处古断层面。地表破裂的野外调查与应力分析结果表明,玉树地震同震地表破裂带总体走向为125°,属于典型的左行走滑破裂带,最大左行走滑位移量1.75m,主压应力为近东西向,这一结果与美国地质调查局和中国地震局地震地球物理研究所公布的结果基本一致。     

玉树7.1级地震断裂特征与地震地表破裂带

2010年4月14日07时49分在青海省玉树县发生了7.1级地震,震中位于 33.2°N,96.6°E,自玉树县城至隆宝镇造成了大量房屋倒塌和人员伤亡.地震发生在NW向的玉树-甘孜断裂西段的玉树-治多断裂上,自隆宝镇东至玉树县城,地震引起了长约50km的地震地表破裂带,主要分布在第三纪红砂岩、高漫滩及河床中,致使公路错断、桥梁位错,并引发大量滑坡和崩滑.震中附近的调查表明,地表破裂带主要沿NW向的玉树-治多断裂展布,总体走向NW320°,分为两组,一组为NW向,另一组为NE向,NW向的破裂为左旋走滑,发育一系列小的类拉分盆地,NE向的破裂表现为正断性质.由震源机制解和断裂特征判定,NW向的玉树-治多断裂为此次地震的发震构造.     

青海玉树地区主要活动断裂的遥感影像解译及构造活动性

综合利用IRS-P5、ALOS、Google earth等高分辨率遥感影像及ASTER DEM资料,结合前人研究成果和野外实地考察,总结玉树地区断裂带的遥感影像解译标志,获取其空间展布和分段情况,对断裂的性质和活动性进行了详细的分析。研究中共解译活动断裂18条,总体呈Y字型分布。通过错断水系位错量的量测、三维地貌对比、地形起伏度和历史地震对比等多种分析,断裂活动强度可以分为强烈、中等和弱活动3个等级,其中当江—多彩断裂、玉树断裂和巴塘断裂是玉树断裂带内最主要的活动断裂。     

青海玉树地区主要活动断裂的遥感影像解译及构造活动性

综合利用IRS-P5、ALOS、Google earth等高分辨率遥感影像及ASTER DEM资料,结合前人研究成果和野外实地考察,总结玉树地区断裂带的遥感影像解译标志,获取其空间展布和分段情况,对断裂的性质和活动性进行了详细的分析。研究中共解译活动断裂18条,总体呈Y字型分布。通过错断水系位错量的量测、三维地貌对比、地形起伏度和历史地震对比等多种分析,断裂活动强度可以分为强烈、中等和弱活动3个等级,其中当江—多彩断裂、玉树断裂和巴塘断裂是玉树断裂带内最主要的活动断裂。     

新构造、活动构造与地震地质

新构造、活动构造和地震地质研究都是开展地震危险性评价的重要基础性地质工作。在综述新构造、活动构造和地震地质的基本含义、相互联系与区别、主要工作内容及方法的基础上,简要回顾了国内外在相关研究领域的主要进展,提出了中国活动构造与地震地质工作中应注意的主要问题和对未来工作的几点建议。最后,重点介绍了青藏高原东南缘开展活动构造体系和玉树地区活动断裂与地震地质调查研究工作所取得的主要进展与成果。     

巴颜喀喇断块边界断裂强震活动分析

断裂带上的地震活动,尤其是现代强震活动,一直是活动构造研究的重要内容.随着研究的深入,研究的对象也从一条断裂带上的强震活动,发展到多条断裂带所构成的空间内的强震活动和断块的强震活动.汶川地震和玉树地震后,巴颜喀喇断块的活动引起了广泛的关注.本文从巴颜喀喇断块整体运动的角度出发,根据断块周边各条断裂带上1900年以来的历史强震记录(Ms≥7)和现代强震活动,分析了断块的地震活动及其准周期性、震源机制、最大震级以及边界走滑断裂与强震活动的关系,主要的认识有:①1900年以来,地震活动呈现出3个地震系列,即:1923～1937年叠溪—花石峡地震系列、1947～1976年达日—炉霍地震系列和1997年开始的昆仑汶川地震系列;②地震系列之间的时间间隔和每一次地震系列持续时间有较大的差异,达日—炉霍地震系列与前后两次地震系列差别较大,而昆仑—汶川地震系列尚未结束;③经过2次8级和8级以上大地震之后,昆仑汶川地震系列虽然尚未结束,今后还可能发生较大地震,但是巴颜喀喇断块很可能已经历了本地震系列的大释放阶段,在该地震系列时间范围内大释放阶段之后的地震震级将小于大释放阶段的震级;④走滑断裂是控制巴颜喀喇断块运动的主要边界断裂,走滑型强震是地震系列的主体;⑤印度板块向北存在一个强烈的推挤过程,是使这些边界断裂带从孕震到真正发生强震的重要条件.     

Compressive Tectonics around Tibetan Plateau Edges

Various earthquake fault types, mechanism solutions, stress field, and other geophysical data were analyzed for study on the crust movement in the Tibetan plateau and its tectonic implications. The results show that numbers of thrust fault and strike-slip fault type earthquakes with strong compressive stress near NNE-SSW direction occurred in the edges around the plateau except the eastern boundary. Some normal faulting type earthquakes concentrate in the Central Tibetan plateau. The strikes of fault planes of thrust and strike-slip faulting earthquakes are almost in the E-W direction based on the analyses of the Wulff stereonet diagrams of fault plane solutions. This implies that the dislocation slip vectors of the thrust and strike-slip faulting type events have quite great components in the N-S direction. The compression motion mainly probably plays the tectonic active regime around the plateau edges. The compressive stress in N-S or NE-SW directions predominates earthquake occurrence in the thrust and strike-slip faulting event region around the plateau. The compressive motion around the Tibetan plateau edge is attributable to the northward motion of the Indian subcontinent plate. The northward motion of the Tibetan plateau shortened in the N-S direction encounters probably strong obstructions at the western and northern margins.     

青藏高原东缘区域地壳稳定性评价

青藏高原东缘新构造运动复杂而强烈,地震与地质灾害多发,区域地壳稳定性评价工作意义重大。基于地质力学和大陆动力学相互补充的区域地壳稳定性评价理论,选择深部地球物理场、区域构造变形、地震活动、区域构造应力场作为内动力因素,地形地貌、降雨量、河流冲蚀组合计算所产生的地质灾害条件作为外动力因素,地层岩性和活动断裂影响带作为介质因素,进行了区域地壳稳定性评价。结果表明,采用地质要素梯度来反映内动力作用和通过地质环境要素综合分析表现外动力作用是提高评价准确性的有效手段;青藏高原东缘可分为8个构造特征差异显著的一级分区,75个综合因素差别较大的二级分区,653个外动力条件有一定差别的三级分区;总体而言,龙门山断裂、鲜水河断裂和安宁河断裂带构成的Y字型构造格架断裂带附近的地壳稳定性最差,西部次之,东部最好,北部区块较完整,南部复杂破碎。     

青藏高原中段活动断层运动速度及驱动机理

在大比例尺活动断层勘测调查基础上,通过测定典型断层位移和活动时代,计算重要活动断层运动速度,分析青藏高原中段地壳水平运动规律。发现青藏高原中段晚更新世～全新世发育大量iW-iWW一近EW向活动断裂,其中昆仑山活动断裂、可可西里南缘活动断裂、通天河活动断裂、崩错活动断裂、念青唐古拉山东麓活动断裂和雅鲁藏布江活动断裂水平运动速度达6～10mm／a,风火山活动断裂、乌丽活动断裂和雁石坪活动断裂水平运动速度达3～4mm／a,唐古拉山活动断裂与格仁错活动断裂水平运动速度约2mm／a。自晚更新世以来,青藏高原中段存在显著的地壳东向运动,相对于柴达木地块的地壳东向运动速度自南北两侧向中部逐步增大,至唐古拉山地区达最大值约40mm／a。青藏高原中段断裂活动、地壳运动与近SN向构造挤压及地壳内部东向水平剪切存在动力学成因联系。     

Active Faulting Pattern,Present-day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region.It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field,except for the west Qinling range where it parallels the striking of the major strike-slip...     

Cenozoic reactivation along the Late Triassic Ganzi-Litang suture,eastern Tibetan Plateau

The spatial-temporal development of Cenozoic reactivation along Mesozoic suture zones in the Tibetan Plateau are first-order parameters needed for assessing models of plateau growth. The Ganzi-Litang suture, in the eastern Tibetan Plateau, developed in the Late Triassic because of subduction and closure along the eastern branch of the Paleo-Tethys Ocean. Near the city of Litang, the Ganzi-Litang suture is defined by a mélange sequence with fault-bound, synorogenic nonmarine strata along the western and eastern flanks, suggesting post-Triassic structural reactivation. We present detrital zircon U–Pb geochronology and field data to determine the timing and style of reactivation along the Ganzi-Litang suture, as well as sedimentary provenance of nonmarine strata.A reverse fault placing mélange rock on top of nonmarine strata along the eastern flank of the Ganzi-Litang suture indicates a contractional deformational regime during reactivation. Conglomerate clast counts indicate a local sediment source of recycled Ganzi-Litang suture and Yidun terrane rock. Detrital zircons indicate a localized provenance consisting of recycled material from Triassic Yidun Arc plutons and Triassic Yidun Group turbidite rock. A weighted mean average of Cenozoic zircon grains (n ​= ​10) establishes a maximum depositional age of 41.5 ​± ​1.2 ​Ma for nonmarine strata in the Ganzi-Litang suture. We interpret the maximum depositional age of the nonmarine strata to represent the upper-limit for structural reactivation along the Ganzi-Litang suture while undeformed Neogene strata in the suture zone represent the lower-limit; thereby bracketing structural reactivation from ca. 42–25 ​Ma. Our results provide enhanced spatial-temporal resolution for Cenozoic deformation in the eastern Tibetan Plateau.     

汶川特大地震后成都盆地内隐伏断层活动性分析

成都盆地内主要有3条隐伏的活动断裂带,包括大邑断裂带、蒲江-新津断裂带和龙泉山断裂带,它们在第四纪都表现出了一定的活动性."512"汶川特大地震后,笔者实地考察的结果表明,在汶川特大地震中成都盆地中的隐伏断裂没有产生新的活动性,目前成都盆地不存在发生特大地震的危险性,是安全的.     

Active Faulting Pattern,Present‐day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

Abstract: This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike-slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left-slip Kunlun-Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE-striking faults cutting the west Qinling range, which accommodates eastward motion, at 10–14 mm/a, of the Chuan-Qing block. The left-slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan-Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low (2–4 mm/a) and absorbed only a small part of the eastward motion of the Chuan-Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE-ward at 7–9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and rheologically layered. The upper crust seems to be decoupled from the lower crust through a décollement zone at a depth of 15–20 km, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this décollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.     

Paleoearthquake Investigation along the Chenghai Fault Zone since ~500 ka, Southeast Margin of the Tibetan Plateau

The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block, which is surrounded by the Honghe River, Xianshuihe–Xiaojiang, and Jinsha River fault zones. As a mid-continental active fault, it is one of the most important seismogenic fractures in the southeast margin of the Tibetan Plateau. Geological seismic study is an important supplement to the historical seismic record; therefore, identification of paleoearthquake events in this region is of great significance to reveal the pattern and mechanism of earthquake development. In this study, detailed investigation has been carried out on the earthquake traces that formed in the Quaternary sediments in the Jinsha River section of the Chenghai fault zone, and samples for dating chronology testing were also collected. Many paleoearthquake traces were discovered in the field, including earthquake fissions, dammed lake sediments and landslides, earthquake-generated rock falls, seismic faults, and sand liquefaction veins. The collected samples were tested using optically stimulated luminescence, electron-spin resonance, and U-series methods. A total of 68 chronological samples were dated, combined with the results of field investigations, and 10 large paleoearthquake events were discovered in this region since 500 ka, which are at approximately 450, 400, 345, 300, 250, 190, 155, 105, 75, and 25 ka. Ten tectonic activity periods that produced multiple paleoearthquake events were identified since 500 ka. This study identifies paleoearthquake events in longer scales, larger spaces, and more extensive sediments, which provides new perspectives and new ideas for paleoearthquake research.