海原断裂干盐池探槽揭示非特征性古地震序列

海原断裂是青藏高原东北缘一条重要的陆内活动左旋走滑断裂,于1920年发生过里氏8?级特大地震,形成约230km的地表破裂带和高达10.2m的同震左旋位移。该断裂的大地震复发行为特征一直是地震地质学家关注的重点,然而现有的认识需要更多以精细沉积地层约束的古地震数据的验证。基于此,在海原断裂中段干盐池盆地成功开挖了数个大型三维探槽,揭露了清晰的韵律性、面状展布地层和丰富的古地震事件证据。在探槽上部2.5m厚的最新细粒沉积层序记录了AD 1500以来的3次地震事件。基于地层中~(14)C样品的结果和历史地震史料的考证,限定这3次地震事件分别对应于AD 1920年、AD 1760年(或1709年)和AD 1638年的地震,但其震级差别很大。除了最新一次地震,即1920年海原大地震的震级为8?级,其他2次地震事件的震级较小,均小于7级,说明海原断裂上伴生有地表破裂的地震不全是特征型地震事件。结果表明,古地震探槽中揭示的地震强度不一定相同,而且中等震级地震也可以产生地表破裂,其地层证据在合适的条件下,如无沉积间断、沉积速率大等环境能在地层中得到保存。     

The Manyas fault zone (southern Marmara region,NW Turkey): active tectonics and paleoseismology

The Manyas fault zone (MFZ) is a splay fault of the Yenice Gönen Fault, which is located on the southern branch of the North Anatolian Fault System. The MFZ is a 38 km long, WNW–ESE-trending and normal fault zone comprised of three en-echelon segments. On 6 October 1964, an earthquake (Ms = 6.9) occurred on the Salur segment. In this study, paleoseismic trench studies were performed along the Salur segment. Based on these paleoseismic trench studies, at least three earthquakes resulting in a surface rupture within the last 4000 years, including the 1964 earthquake have been identified and dated. The penultimate event can be correlated with the AD 1323 earthquake. There is no archaeological and/or historical record that can be associated with the oldest earthquake dated between BP 3800 ± 600 and BP 2300 ± 200 years. Additionally, the trench study performed to the north of the Salur segment demonstrates paleoliquefaction structures crossing each other. The surface deformation that occurred during the 1964 earthquake is determined primarily to be the consequence of liquefaction. According to the fault plane slip data, the MFZ is a purely normal fault demonstrating a listric geometry with a dip of 64°–74° to the NNE.     

Palaeoseismicity of the Dinar fault, SW Turkey

The NW–SE-trending Dinar fault is an active normal fault upon which the 1 October 1995 earthquake ( M  = 6.1) occurred. The 1995 earthquake resulted in a c. 10-km-long surface rupture with the south side down-thrown by 50 cm. Investigations of two trench sites perpendicular to the 1995 rupture suggest at least two prior large earthquakes in historical times. Radiocarbon dates and historical records constrain the age of events between 1500 bc and ad 53, event 2 possibly coinciding with the earthquake that damaged Dinar (the ancient city of Apamea Kibotos) in c. 80 bc and event 1 around 1500 bc. Surface displacements determined for events 1 and 2, compared to the 1995 surface faulting, indicate that M > 6.8 earthquakes were associated with each rupture. Using the total displacement in trenches, a slip rate of about 1 mm yr⁻¹ can be estimated for the Dinar fault. Observations suggest that the return period for large earthquakes in the Dinar area is about 1500–2000 years.     

Stratigraphic evidence for millennial-scale temporal clustering of earthquakes on a continental-interior fault: Holocene Mississippi River floodplain deposits, New Madrid seismic zone, USA

The earthquake cycles that characterize continental-interior areas that are far from active plate boundaries have proven highly cryptic and difficult to resolve. We used a novel paleoseismic proxy to address this issue. Namely, we reconstructed Holocene Mississippi River channels from maps of floodplain strata in order to identify channel perturbations reflective of major displacement events on the high-hazard and mid-plate Reelfoot thrust fault, New Madrid seismic zone, U.S.A. Only three discrete slip events are currently documented for the Reelfoot fault ( AD 900,  AD 1450, and AD 1812). This study extends this record and, thus, illustrates the utility of stratigraphic proxies as paleoseismic tools. We concurrently offer here some of the first quantified response times for tectonically induced channel pattern changes in large alluvial rivers.

We identified at least two cycles of pervasive meandering that were interrupted by channel-straightening responses occurring upstream of the Reelfoot fault scarp. These straightening responses initiated at 2244 BC +/− 269 to 1620 BC +/− 220 and  AD 900, respectively, and each records initiation of a period of Reelfoot fault slip after millennia of relative tectonic quiescence. The second (or New Madrid) straightening response was triggered by the previously known  AD 900 fault slip event, and this initial low sinuosity has been protracted until the modern day by the latter  AD 1450 and AD 1812 events. The first (or Bondurant) straightening response began a period of several hundred to  1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the Reelfoot fault. These Bondurant events predate the existing paleoseismic record for the Reelfoot fault.

These data offer initial evidence that slip events on the Reelfoot fault were temporally clustered on millennial scales and, thus, offers the first direct evidence for millennial-scale clustering of earthquakes on a continental-interior fault. This carries additional ramifications. Namely, faults that have been quiescent and non-hazardous for millennia could re-enter an enduring period of recurrent hazardous earthquakes with little warning. Likewise, the Reelfoot fault also reveals evidence of temporal clustering of earthquakes on short-term cycles (months), as well as evidence for longer-term reactivation cycles (10⁴–10⁶ years). This introduces the possibility that temporal clustering could be hierarchical on some continental-interior faults.     

基于LiDAR的海原断裂松山段断错地貌分析与古地震探槽选址实例

基于高精度机载Li DAR数据在GIS平台的地貌因子渲染分析,对海原断裂老虎山段松山地区古地震研究点进行高精度大比例尺(1∶1000)地貌填图,勾勒出研究点微地貌空间展布和断裂高精度几何形态。通过对松山古地震研究点2个新探槽的开挖,结合细致的探槽解译、地震事件识别与分期、年代学样品测试,得出5次37380±880BP以内的不连续古地震序列。通过对比此处已经开挖的各自相距不足150m、分布于断裂同一段落的4个古地震探槽的微地貌位置、沉积特征和地震事件信号强弱,发现即使相距不远,不同微地貌位置古地震探槽揭示的古地震现象也会有显著差别。这种差别凸显了古地震研究结果,如揭示的事件证据和个数等与探槽点位置的选取有较强的依赖性。综合对比分析表明,较低的地势、低能静水环境、高沉积速率、细粒的沉积物源区及连续的沉积环境是走滑断裂上开展古地震研究的优选地貌位置。实例表明,基于高精度地形数据对研究点开展精细地貌填图揭示微地貌时空演化,从而在探槽开挖前对古地震研究点的构造地貌优劣进行充分评价是提高古地震研究质量的必要程序,同时也显示出高精度机载Li DAR数据在活动构造研究中的重要新应用。     

Four-dimensional transform fault processes: progressive evolution of step-overs and bends

Many bends or step-overs along strike–slip faults may evolve by propagation of the strike–slip fault on one side of the structure and progressive shut-off of the strike–slip fault on the other side. In such a process, new transverse structures form, and the bend or step-over region migrates with respect to materials that were once affected by it. This process is the progressive asymmetric development of a strike–slip duplex. Consequences of this type of step-over evolution include: (1) the amount of structural relief in the restraining step-over or bend region is less than expected; (2) pull-apart basin deposits are left outside of the active basin; and (3) local tectonic inversion occurs that is not linked to regional plate boundary kinematic changes. This type of evolution of step-overs and bends may be common along the dextral San Andreas fault system of California; we present evidence at different scales for the evolution of bends and step-overs along this fault system. Examples of pull-apart basin deposits related to migrating releasing (right) bends or step-overs are the Plio-Pleistocene Merced Formation (tens of km along strike), the Pleistocene Olema Creek Formation (several km along strike) along the San Andreas fault in the San Francisco Bay area, and an inverted colluvial graben exposed in a paleoseismic trench across the Miller Creek fault (meters to tens of meters along strike) in the eastern San Francisco Bay area. Examples of migrating restraining bends or step-overs include the transfer of slip from the Calaveras to Hayward fault, and the Greenville to the Concord fault (ten km or more along strike), the offshore San Gregorio fold and thrust belt (40 km along strike), and the progressive transfer of slip from the eastern faults of the San Andreas system to the migrating Mendocino triple junction (over 150 km along strike). Similar 4D evolution may characterize the evolution of other regions in the world, including the Dead Sea pull-apart, the Gulf of Paria pull-apart basin of northern Venezuela, and the Hanmer and Dagg basins of New Zealand.     

拉分盆地三维演化初探——以新疆富蕴断裂拉分盆地为例

拉分盆地指沿着走滑断裂带弯曲部位,由于拉张而产生的地形上的低洼处,多形成于走滑断裂带次级断裂的间列部位.拉分盆地研究对于探讨走滑断裂扩展方式及分段性意义重大;分布于大型走滑断裂带上的拉分盆地,对于断裂带上地震临震预测具有一定的指示作用;此外,该类盆地往往与油气资源、成矿热液的运移、聚集、产出关系密切.本文在综述前人对拉...     

鲜水河断裂带色拉哈段中谷村一带的最新地表破裂讨论

鲜水河断裂带色拉哈段是2014年康定M_S6.3地震的发震断裂段,其最新一次地表破裂事件(1725年康定7级地震)的离逝时间较长,是最可能发生7级以上地表破裂型大震的危险地段之一。获得色拉哈段最新地震地表破裂的展布范围对确定断裂带的地震活动历史、评估断裂带的未来地震危险性以及防震减灾具有重要意义。然而,迄今色拉哈段最新地表破裂的北西端位置仍存有较大争议。对此,在以往资料认为没有同震地表破裂的中谷村一带开挖了探槽组,获得了这一带的破裂历史,其最新一次事件(E6)的限定年代为A.D.746±51之后。综合探槽剖面证据和附近的断错地貌特征以及历史地震资料,探槽揭露的最新事件E6可能对应1725年康定7级地震,色拉哈段的地表破裂北西端至少已延伸到中谷村一带。     

Late-Cenozoic pull-apart basins, Boconó fault zone, Venezuelan Andes

Several areas along the Boconó fault zone are characterized by elongate, almond-shaped basins containing thick alluvial sequences, mainly of Quaternary age, and bounded by faults with normal Quaternary displacements. These areas are separated by segments characterized by narrow fault traces and right-lateral displacements. The fault-bounded basins are interpreted as pull-apart basins that originated at releasing bends along the fault zone. The size of the La González pull-apart basin suggests that Pliocene (?)-Quaternary right-lateral slip on the Boconó fault zone was of the order of 7–9 km.     

Review of paleoseismological and active fault studies in Taiwan in the light of the Chichi earthquake of September 21, 1999

This paper reviews the research on active and earthquake faults in Taiwan conducted prior and after the 1999 Chichi earthquake. The Chichi earthquake plays as a turning point of the relevant studies, since the 1999 coseismic surface rupture exactly follows preexisting fault scarps, created in turn by previous seismic events along the Chelungpu Fault. This fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes. Since 1999, many trenching studies have been carried out along the Chichi earthquake fault. A few of them demonstrates that the penultimate event is as young as probably only 200–430 years old; however, some others show a rather old age of several hundreds years or even older for the last faulting event before 1999. More trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length. In addition, we further discuss the offshore faulting associated with seismic event along the eastern coast of Taiwan, where the multiple Holocene terraces are well known.     

2010年玉树地震(Ms7.1)地表破裂特征、破裂机制与破裂过程

2010年4月14日,青海省玉树地区发生Ms7.1级地震,造成大量人员伤亡和财产损失.地震发生后,我们对地震地表破裂带进行了详细的考察,并对同震位移量进行了精确的测量.根据野外考察和测量的结果,对玉树地震的地表破裂特征、同震位移量及其分布特征进行了分析,并对地震的破裂机制和破裂过程进行了探讨,取得如下认识:(1)玉树地震形成了沿鲜水河断裂带西北段(甘孜-玉树断裂)分布的东、西两条地表破裂带,西段破裂带分布在微观震中附近的隆宝湖拉分盆地中,长约19km;东段破裂带沿扎曲河南岸及巴塘河西岸山坡展布,长度约31km;上述两条破裂带之间存在约15km的地表破裂空区;(2)野外测量获得玉树地震的最大同震位移量为2.3m,位于东段地表破裂带中部郭央烟宋多附近;(3)地表破裂和野外构造地貌特征均反映了发震断层处于走滑伸展环境,断层左旋走滑过程中伴随正断作用;(4)地震波反演结果和地表破裂分布特征表明,玉树地震的破裂过程包括两次子事件,分别在地表形成了隆宝湖破裂带和扎曲河、巴塘河破裂带,隆宝湖及玉树县城西侧的山间谷地是在甘孜-玉树断裂长期活动的破裂带阶区转换拉张过程中形成的两个拉分盆地.     

滇西北程海断裂带主要古地震滑坡及其分布特征的构造解释

位于红河断裂带西北端,滇西北断陷带东侧的程海断裂带第四纪活动显著,沿断裂盆山地貌与高山峡谷地貌发育,地质灾害频发.综合利用目视解译与野外调查,对程海断裂带沿线滑坡调查发现,沿程海断裂带共发育各类滑坡940余个,含巨型滑坡61个、大型滑坡125个、中型滑坡316个、小型滑坡438个.这其中有32个巨型滑坡、61个大型滑坡...     

Morphotectonics and paleoseismology of the eastern end of the Bolnay fault (Mongolia)

The Bolnay (Hangayn) fault is an active shear system which generated the M = 8.2-8.5 Bolnay earthquake of 23 July 1905, one of world’s largest recorded intracontinental event. The fault follows the Mesozoic suture formed during the closure of the Mongolia-Okhotsk ocean. The Late Cenozoic faulting in the region was induced by propagation of strain from the India-Eurasia collision that had reached Mongolia at about 5 ± 3 Ma. The left-lateral strike slip almost all over the fault length is compensated in its western end by Late Quaternary reverse motion. We estimated coseismic slip associated with the event of 1905 and the previous earthquakes in the eastern fault end and checked whether vertical offset compensates the strike slip in this part as well. The 1905 coseismic slip measured from a displaced dry stream bed and pebble bars in the Hasany-Gol river valley was 6.5-7.5 m. The 13 ± 1 m left-lateral displacement of pebble bars in the same valley represents a cumulative slip of two events. Paleoseismological studies across the strike of surface ruptures reveal at least two generations of rupture in two events that postdated the deposition of sediments with a ¹⁴C age of 4689 ± 94 yr. Hypsometry of the alluvial surface in the zone of deformation shows gradual elevation increase toward the mountains, but without abrupt change across the fault. This means the absence of vertical offset and reactivation of the fault as a left-lateral strike slip. The horizontal slip in the eastern extension of the Bolnay fault is compensated rather by parallel fault-bounded pull-apart basins trending northeastward oblique to the principal fault strike. The age of their sedimentary fill suggests no older than middle Pleistocene normal faulting that compensated the Bolnay strike slip.     

Relationship of late Quaternary tectonics and volcanism in the Khanarassar active fault zone, the Armenian Upland

The Syunik rhombus-like structure in the Khanarassar active dextral fault zone of Armenia is a typical pull-apart basin, formed between terminal parts of two adjacent en echelon fault segments. Some component of subsidence associated with the faults of the structure is found between the en echelon segments; nevertheless, the dextral component continues to be predominant even on the boundaries of the pull-apart basin. The late Pleistocene and Holocene lava volcanoes of the basin are also associated with those faults that have a component of extension. The relative ages of fault displacements and volcanic eruptions have been identified by the mutual correlation of lavas, moraines and topographic features and by archaeological and radiocarbon dating. According to the interpretation of rupturing and volcanism, major earthquakes and volcanic eruptions appear inter-related and three pulses of such activity during the earlier and middle Holocene have been identified.     

Late Quaternary Large Earthquakes on the Western Branch of the Xiaojiang Fault and Their Tectonic Implications

The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan Plateau.The largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral displacement of ~ 6.9 m, occurred on the western branch of the Xiaojiang fault.Studying this fault is important in understanding current deformation and kinematic characteristics of the Tibetan Plateau.Activities and stretches have been well undertaken on the Xiaojiang fault, while paleoseismic research work is always the weak link on this fault.To investigate the paleoseismic history and large earthquake activity of the Xiaojiang fault, we opened a large trench at the northern edge of Caohaizi sag pond on the western branch of the Xiaojiang fault.Six paleoseismic events have been identified, and named E1 through E6 from the oldest to the youngest.Charcoal and woods are abundant, 20 samples were dated to constrain the ages of the paleoseismic events at 40 000–36 300 BC, 35 400–24 800 BC, 9 500 BC–AD 500, AD 390–720, AD 1120–1620 and AD 1750–present.We associate the youngest event E6 with the 1833 M8 earthquake.Events E4, E5 and E6 show a continuous record of the western strand of the Xiaojiang fault in the late Holocene, with a average recurrence interval of 370–480 yr.Large earthquake recurrence in the late Holocene is far less than the recurrence of 2000–4000 yr posed in previous studies.Thus, the seismic hazard on the Xiaojiang fault should be reevaluated.Furthermore, the irregular recurrence of large earthquakes on the Xiaojiang fault and other faults in the Xianshuihe-Xiaojiang system, indicates the uneven southeastward extrusion of the Sichuan-Yunnan block along the southeastern margin of the Tibetan Plateau.     

青藏高原北部第四纪早期断裂活动的 新生性变化初步研究*

关于第四纪早期构造事件的年代学研究取得了大量数据,但对构造事件的表现形式缺乏认识。文章通过对海原断裂带内拉分盆地演化趋势及年代学研究,认为海原断裂带内的最新拉分盆地形成于1.6MaB.P.之后,代表一次新断裂的形成时期,且新断裂走向与先存断裂有一定的逆时针夹角。通过对青藏高原中部可可西里-东昆仑断裂带构造地貌的遥感解译和强震破裂调查,认为可可西里-东昆仑断裂带是一条具有新生性的强震构造带,新断裂形成时期为1.10~0.65MaB.P.之间,其构造带内的新生性断裂走向与先存断裂亦有一定的逆时针方向夹角。两条断裂带具有一致的演化趋势,说明在早更新世中后期存在区域性的构造事件,该事件表现为一系列新生性断裂的产生。     

Pull-apart origin of the Satpura Gondwana basin, central India

The Gondwana basins of peninsular India are traditionally considered as extensional-rift basins due to the overwhelming evidence of fault-controlled synsedimentary subsidence. These basins indeed originated under a bulk extensional tectonic regime, due to failure of the attenuated crust along pre-existing zones of weakness inherited from Precambrian structural fabrics. However, disposition of the basins and their structural architecture indicate that the kinematics of all the basins cannot be extensional. To maintain kinematic compatibility with other basins as well as the bulk lateral extension, some basins ought to be of strike-slip origin. The disposition, shape and structural architecture of the Satpura basin, central India suggest that the basin could be a pull-apart basin that developed above a releasing jog of a left-stepping strike-slip fault system defined by the Son-Narmada south fault and Tapti north fault in consequence to sinistral displacement along WSW-ENE. Development of a sedimentary basin under the above-mentioned kinematic condition was simulated in model experiments with sandpack. The shape, relative size, stratigraphic and structural architecture of the experimental basin tally with that of the Satpura basin. The experimental results also provide insights into the tectono-sedimentary evolution of the Satpura basin in particular and pull-apart basins in general.     

Discrete Element Modeling of a Subduction Zone with a Seafloor Irregularity and its Impact on the Seismic Cycle

Seafloor irregularities influence rupture behavior along the subducting slab and in the overriding plate, thus affecting earthquake cycles. Whether seafloor irregularities increase the likelihood of large earthquakes in a subduction zone remains contested, partially due to focus put either on fault development or on rupture pattern. Here, we simulate a subducting slab with a seafloor irregularity and the resulting deformation pattern of the overriding plate using the discrete element method. Our simulations illustrate the rupture along three major fault systems: megathrust, splay and backthrust faults. Our results show different rupture dimensions of earthquake events varying from tens to ca. 140 km. Our results suggest that the recurrence interval of megathrust events with rupture length of ca. 100 km is ca. 140 years, which is overall comparable to the paleoseismic records at the Mentawai area of the Sumatran zone. We further propose the coseismic slip amounts decrease and interseismic slip amounts increase from the surface downwards gradually.     

Paleoseismological evidence for non-characteristic behavior of surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan

The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, M_JMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior.     

玉树断裂带左旋走滑活动标志及其几何学 与运动学特征

玉树断裂带位于甘孜-玉树断裂带北西段,是一条总体呈NWW向展布的左旋走滑活动断裂带.沿断裂带发育错断水系与冲沟、拉分盆地、地震地表破裂与断裂破碎带等一系列反映玉树断裂带左旋走滑活动的典型地质-地貌标志.在室内遥感解译的基础上,结合最新的野外实地调查成果,对沿玉树断裂带上反映其左旋走滑活动的地质-地貌标志进行了总结,并对断裂带的几何学与运动学特征进行了综合分析.结果表明,玉树断裂带总长约150km,总体走向120～130°,自西向东可划分为呈左阶雁列分布的陇蒙达-结隆段、结隆-结古段和结古-查那扣段3段.沿该断裂带发育的串珠状拉分断陷盆地规模的大小反映出玉树断裂带自西向东拉张效应逐渐减弱、挤压效应逐渐增强的特点.玉树2010年7.1级地震的宏观震中处于晚第四纪活动性最为显著的中段,而仪器震中恰好处于该断裂带的不连续部位,进一步证明雁列走滑活动断裂带上的不连续部位通常是强震活动的初始破裂区域.