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1.
Extended horizons of 0.5–2-m-thick soft-sediment deformation structures, which were earlier described as the effects of strong earthquakes in the Late Pleistocene, are studied in glaciolacustrine deposits of the Khibiny massif (central part of the Kola Peninsula). The unstructured horizon of coarse-fragmental inclusions is found everywhere over the folds, which makes it possible to consider these structures as the result of debris flow impact on consolidated bottom sediments probably caused by glacial mudflow. Despite intense and instantaneous crumpling of sediments, no liquefaction or fluidization phenomena typical of seismites are recognized in the deformation structures. Thus, the new data on the genesis of folded horizons in glaciolacustrine sediments in the Khibiny massif does not confirm the high seismic potential of this region.  相似文献   

2.
More than 80 layers of seismites were recognized from the Early Cretaceous Dasheng Group in the Mazhan and Tancheng graben basins in the Tanlu Fault Zone, eastern China. The responsible seismic events took place about 110–100 Ma in the Early Cretaceous. The fault zone was affected at the time by strong tectonics, due to tension-related stretching and scattered squeezing by strike-slip faults. These tectonic activities induced a series of strong earthquakes with Richter magnitudes(M) of 5–8.5. The earthquakes affected saturated or semi-consolidated flood and lake sediments, and produced intra-layer deformations by several processes, including liquefaction, thixotropy, drop, faulting, cracking, filling and folding, which resulted in the formation of various soft-sediment deformation structures, such as dikes and veins of liquefied sand, liquefied breccias, liquefied homogeneous layers, load structures, flame structures, ball-and-pillow structures, boudinage, diapirs, fissure infillings, a giant conglomerate wedge, and syn-sedimentary faults. The seismites are new evidence of tectonic and seismic activities in the Tanlu Fault Zone during the Early Cretaceous; the series of strong seismic events that can be deduced from them must be considered as a response to the destruction of the North China Craton.  相似文献   

3.
A lot of seismic volcanic rocks and strong earthquake-induced thixotropic deformation structures in soft mud-sandy sediments(seismites)were identified from the Upper Cretaceous Shijiatun Member of the Hongtuya Formation for the first time in Jiaozhou City of the Zhucheng Sag, eastern China. Seismic volcanic rocks are volcanic rocks with co-seismic deformation structures which were produced by major earthquakes destroying volcano ejecta. Seismites are sediment layers with soft-sediment deformation structures formed by strong earthquake triggering saturated or semi-consolidated soft sediments to produce liquefaction, thixotropy, faults, cracks and filling and so forth. The Shijiatun Member of the Hongtuya Formation mainly consists of basaltic volcano rocks interbedded with mud-sandy(muddy sand and sandy mud)deposition layers of the river-lake facies. In the Shijiatun Member, main types of seismic volcanic rocks are shattered basalts with co-seismic fissures and seismic basaltic breccias. The thixotropic deformations of soft mud-sandy sediments mainly include thixotropic mud-sandy veins and thixotropic mud-sandy layers with tortuous boundaries. Under the strong earthquake action, saturated mud-sandy sediments could not be liquefied, instead resulting in thixotropy, i.e. their texture can be damaged and their flow-ability or rheology becomes strong. Because basaltic volcano rocks were damaged(shattered, seismic broken), a major earthquake can lead to thixotropic mud-sandy sediments flowing along seismic fissures in basalts, resulting in the formation of deformation structure of thixotropic veins, and boundaries between volcano rock and mud-sand layer became quite winding. Under the koinonia of gravity and vibration force, seismic breccia blocks sunk into thixotropic mud-sandy layers, resulting in the formation of inclusions of thixotropic mud-sandy sediments. Seismic intensity reflected by these strong earthquake records during the end stage of the Late Cretaceous was about Ⅶ to more than X degrees. The Shijiatun Member is mainly distributed in the south of the Baichihe fault in the northern Zhucheng Sag, and the fault has generated many strong tectonic and earthquake activities at the end of the late Cretaceous, also provided the channel for intrusion and eruption of basaltic magma then. At the end of the late Cretaceous, intermittent intrusion and eruption of basaltic magma took place along the Baichihe fault, meanwhile the volcano earthquakes took place or tectonic earthquakes were generated by the Baichihe fault which caused the deformation of the volcano lava and underlying strata of red saturated muddy-sand, resulting in the formation of various seismo-genesis deformations of volcanic rocks interbedded with mud-sandy sediment layers. Therefore, strong seismic events recorded by them should be responses to strong tectonic taphrogenesis of the Zhucheng Sag and intense activity of the Baichihe fault in the end of Late Cretaceous. In addition, these seismogenic deformation structures of rock-soil layers provide new data for the analysis of the failure effect produced by seismic force in similar rock-soil foundations.  相似文献   

4.
The Cane Run Bed is a prominent unit of micrograined limestone and shale of distal storm origin in the lower part of the Late Ordovician (late Chatfieldian; late Caradoc) Lexington Limestone (Trenton) in central Kentucky, USA. The unit's prominence relates to presence of up to three horizons of penecontemporaneous, soft-sediment deformation that form a distinctive event bed; equivalent horizons of different lithology are also deformed. Concurrence of four lines of evidence, including deformation consistent with a seismogenic origin, widespread distribution in temporally and stratigraphically constrained horizons, a pattern of increasing frequency or deformation intensity toward likely epicentral areas, and the ability to exclude other likely causes, points strongly to a seismogenic origin for each horizon. This interpretation is bolstered by the facts that the deformation contains random fold axes, crosses facies boundaries, is associated with a periodically reactivated basement structural lineament, and crosscuts undeformed beds from both above and below. Moreover, mapping the distribution of deformation intensity allows for the interpretation of possible epicentral areas. The association of Cane Run deformation with other sedimentologic-stratigraphic anomalies related to reactivated basement faults, as well as their coincidence with the inception of a Taconian tectophase, suggest that Cane Run seismites are one of several responses to the distal transmission of far-field forces from the coeval Taconian orogeny into the foreland, largely via zones of basement structural weakness. Units like the Cane Run Bed and its equivalents, whose seismogenic origins can be confidently demonstrated, suggest that seismicity must have had a substantial influence at times on epicontinental sedimentation, even in seas far removed from orogenic sources of stress.  相似文献   

5.
Clastic dikes are formed either by passive deposition of clastic material into pre-existing fissures (depositional dikes), or by fracturing and injection of clastics during earthquakes (injection dikes). We proposed to use optically stimulated luminescence (OSL) dating to distinguish between the two modes of formation and hypothesized that (1) depositional dikes filled from above show OSL ages younger than the host rock; and (2) injection dikes filled from below show the same OSL ages as that of the host rock. We studied the mechanisms of clastic-dike formation and their ages within the seismically active Dead Sea basin, where hundreds of dikes crosscut the late Pleistocene (70–15 ka) lacustrine sediments of the Lisan Formation. Field observations and analysis of magnetic tensors show unequivocally that most of these dikes were emplaced by injection, inferred to be due to seismically triggered fluidization–liquefaction during earthquakes. Twenty-eight samples were collected from the Lisan source material and dikes that, based on field observations, are unmistakably either depositional dikes or injection dikes.

Quartz single aliquot OSL ages of the source Lisan layers are between 43 and 34 ka, and are typical for the Lisan Formation. The ages of both depositional and injection dikes are between 15 and 17 ka, younger than the Lisan host rock. Depositional dikes show a highly scattered distribution of single grain ages, suggesting several episodes of infill. Single grain ages of injection dikes are of latest Pleistocene to Holocene, and do not contain recently bleached grains that infiltrated from above. These results imply that the OSL signals were reset at the time of fluidization–liquefaction and buildup of fluid pressure within the injection dikes. If this resetting mechanism has a physical ground, then OSL dating is an important tool for constraining the ages of earthquake-induced injection dikes and recovering paleoseismic data from them.  相似文献   


6.
岷江上游堰塞湖沉积中软沉积物变形构造成因讨论   总被引：3，自引：0，他引：3  
对在岷江上游及其支流河谷中的晚第四纪古堰塞湖地层中发现的大量软沉积物变形构造的类型、特征和成因进行了分析,发现这些软沉积物变形构造分为两类:一类是小型的层内变形构造,如液化卷曲变形、泄水构造、负荷构造、阶梯状微断裂等,其形成与软沉积物的塑性变形、液化和流动作用相关;另一类是崩(滑)塌体对软沉积物的扰动形成的大型褶曲构造.通过与其它成因的软沉积物变形构造的对比以及对区域构造环境的分析,得出地震、崩塌和滑坡等灾害性地质事件是造成河谷区古堰塞湖地层中软沉积物变形构造发育的最可能的驱动机制.  相似文献   

7.
Evidence of ancient liquefaction-in duced features is presented in the area of the 2003 Zemmouri earthquake (M w 6.8). This earthquake was related to an offshore unknown 50-km long fault. A 0.55-m coseismic coastal uplift was generated and extensive liquefaction has been induced in the most susceptible area which correspond to the seaside and along the hydrographic network, mainly the Sebaou and Isser valley rivers. Field investigations allowed us to identify past liquefaction traces in the Quaternary deposits. The observed features are represented by sand dikes, sills, and sand vents as well as well-preserved sand boiled volcanoes. In this work, we also describe the alluvial environment, the hosted localized stratigraphic layer, the morphology and the geometry of the observed features, as well as the observed deformation (settlement) of the hosted layers that are among characteristics of the seismically induced features as described in worldwide examples. Our observations represent a step towards paleoseismological studies in the region knowing that the May 21st 2003 Zemmouri earthquake is produced by an offshore fault where a direct study of the seismogenic fault is inaccessible.  相似文献   

8.
在河北省北部柳江盆地发现了距今5亿年前的地震记录。 震积岩发育在上寒武统崮山组中部。 沉积物变形构造主要有地裂缝、 地震楔、 砂脉、 砂层液化、 包卷层理等。 这些特征沉积构造是地震波作用于潮上—潮间带沉积环境中软沉积物而形成的。 在古沙垄顶部的内碎屑微晶灰岩中有沉积物液化产生扰动层理和流体逃逸形成的砂脉。 显微镜下可见沉积物液化流动显微构造和结构, 如微褶皱、 纹层断错、 液化颗粒等。 水面下在生物礁或沙垄斜坡局部可见重力流形成的包卷层理。 包卷层理核部为浅黄色和紫红色竹叶状灰岩, 中部为浅灰色破碎流化微晶灰岩碎屑, 外部为浅色和紫色内碎屑微晶灰岩。 崮山组的岩性组合和这些软沉积物变形构造表明, 崮山期柳江盆地构造活动剧烈, 沉积环境水深反复变化、 逐步变浅, 伴有地震发生, 估计产生震积岩的古地震的强度为7级左右。 该古地震事件的确定有益于研究地震活动和构造活动规律。  相似文献   

9.
Thin, discontinuous remnants of Neoproterozoic intracratonic rift-basin deposits of the Chestnut Hill Formation occur in the western New Jersey Highlands. These deposits form an important link between well-documented Iapetan rift-basins in both the northern and southern Appalachians. The close spatial relations of Chestnut Hill rocks to Paleozoic sedimentary rocks open the possibility that additional Iapetan rift-basins could be concealed beneath the rocks of the Valley and Ridge Province to the west indicating a much broader zone of rifting than has been previously proposed. The Chestnut Hill Formation is intermittently exposed along a 100 km-long band that extends northeast from Pennsylvania nearly to New York State. The lower part of the Chestnut Hill Formation is composed of interbedded lithic pebble- to boulder-conglomerate and feldspathic sandstone grading upward into interbedded phyllite, feldspathic and quartz sandstone, local paleosaprolite, quartz-pebble conglomerate, thin limestone lenses, volcanic, and volcaniclasic rocks, abundant bedded ironstone (hematite ore), and ultimately into diamictites that are interpreted as possible tilloids and containing rounded intra and extrabasinal clasts of the other lithologies. Extensive soft-sediment deformation, cross bedding, and clastic dikes are common in all but the lowest and upper facies. Banded hematite layers occur preferentially in fine-grained tuffs and tuffaceous sediments, but hematitization has affected most lithologies. Volcanic rocks consist of altered rhyolitic tuffs and lapilli tuffs that are interbedded with sediments. The Chestnut Hill Formation is interpreted to have been deposited in early alluvial, and later a complex of fluvial, lacustrine and deltaic environments. Provenance studies based upon petrographic and geochemical analysis of clastic rocks indicate that the sediments are predominantly immature and reflect derivation from local uplifted felsic basement sources in a rifted-margin tectonic setting. Low to moderate weathering of the source rocks is indicated by the geochemistry of most samples, as is the locally intense effect of hydrothermal alteration. Most occurrences of the Chestnut Hill Formation are associated with major faults that exhibit normal movement of apparent Neoproterozoic age. Rocks from the Morgan Hill fault near Easton, Pennsylvania display consistent normal shear sense and vary from low temperature S-C mylonites to breccia that contains deformed pieces of Chestnut Hill Formation.  相似文献   

10.
Coastal Quaternary deposits of western Oranie show typical soft-sediment deformations including sedimentary dykes, sand volcanoes, sismoslumps, thixotropic bowls, thixotropic wedges, diapir-like structures, and faults grading. Field observations indicate that these deformations exist at several levels of the studied deposits along the west Oranian coast. This study demonstrated that these structures are earthquakes-related, by analysis of potential trigger sources. Several arguments demonstrate the seismic origin: the depositional environment rich in water that located in an active tectonic region, the thixotropic nature of deformations and their large vertical and horizontal diffusion in the Quaternary series consistent with a seismic recurrence. This allows characterizing these Quaternary soft-sediment deformations as seismites that were triggered by earthquakes.  相似文献   

11.
The origin of dike-like bodies along the Hilina fault scarp on the south flank of Kilauea Volcano. Hawaii has been the subject of recent controversy. Some geologists favour an origin by intrusion of magma from below, others favour « intrusion » of lava derived from above — lava derived from fluid surface flows which poured down open cracks. In order to distinguish between deep versus surface sources for the bodies, a suite of dike and other samples were analyzed for S, H2O, and Cl. All surface flows are degassed, whereas known dikes are volatile-rich. Samples of the Hilina dikes, and dikes from the Ninole Formation, Mauna Loa are degassed, indicating that these dikes were surface-fed — formed by magma which had been de-volatized by surface transport. A model is presented whereby the Hilina dikes form in talus and lava cones that drape the Hilina fault scarp. Seismic activity during eruption may have played an important role in the formation of the Hilina dikes. Similar dikes in the Ninole Formation probably formed in a similar environment.  相似文献   

12.
通过大探槽开挖和断层陡坎分析，揭示出发生于１６７９年８级地震的新夏垫断层自距今约２万ａ以来共发生了４次地震事件。前两次为砂体液化显示的事件；后两次为可见直接断错证据的事件。分析得到的１６７９年地震最大垂直位移为１．７５ｍ，前１６７９年事件为１．４１ｍ，是两次震级非常接近的特征地震。４次事件发生的时间分别为距今约２００００，１３０００，７５００和３１７ａ，平均重复间隔时间为（６５６１±６９１）ａ，显示了准周期重复的特征  相似文献   

13.
To better image deformation structures within the inner accretionary wedge of the Nankai Trough, Japan, we apply common reflection angle migration to a legacy two-dimensional seismic data set acquired with a 6 km streamer cable. In this region, many seismic surveys have been conducted to study the seismogenic zone related to plate subduction. However, the details of the accreted sediments beneath the Kumano forearc basin are still unclear due to the poor quality of seismic images caused by multiple reflections, highly attenuated signals, and possibly complex geological structures. Generating common image gathers in the subsurface local angle domain rather than the surface offset domain is more advantageous for imaging geological structures that involve complex wave paths and poor illumination. By applying this method, previously unseen structures are revealed in the thick accreted sediments. The newly imaged geometric features of reflectors, such as the folds in the shallow part of the section and the deep reflectors with stepwise discontinuities, imply deformation structures with multiple thrust faults. The reflections within the deep accreted sediments (approximately 5 km) are mainly mapped to far angles (30°–50°) in the common reflection angles, which correspond to the recorded offset distances greater than 4.5 km. This result indicates that the far offset/angle information is critical to image the deformation structures at depth. The new depth image from the common reflection angle migration provides seismic evidence of multiple thrust faults and their relationship with the megathrust fault that is essential for understanding the structure and evolution of the Nankai Trough seismogenic zone.  相似文献   

14.
在对2013年4月20日芦山MS7.0地震灾区大量地震地质灾害实地考察及调查的基础上, 总结了滑坡、 崩塌、 砂土液化、 地裂缝、 地表变形等地震地质灾害的分布及发育特点, 探讨了地震地质灾害与发震断裂之间的关系. 极震区和重灾区的崩塌和滑坡特别严重, 是地震巨大破坏作用的外在表现形式; 砂土液化点较少, 分布范围和规模有限; 地裂缝和地表变形并非真正意义上的地震地表破裂带. 根据极震区和重灾区地震地质灾害的分布和发育特点, 认为芦山地震最有可能的发震断裂为龙门山前山断裂的双石—大川断裂, 也有可能是龙门山山前隐伏断裂的大邑断裂, 还有可能是双石—大川断裂与大邑断裂两者共同触发的结果.   相似文献   

15.
Instability structures, synsedimentary faults and turbidites have been studied in the Lower Pliensbachian succession of Saint-Michel-en-Beaumont, belonging to the Taillefer block, an ancient half-graben emplaced during the Liassic Tethyan rifting. Geometrical and mechanical analyses demonstrate that the instability structures occurred thanks to movements along spineless synsedimentary normal faults, when the turbiditic and limestone layers were already case-hardened and partly fractured by tension gashes even when the mudstones were still unlithified. Both the tension gashes and the synsedimentary faults are homogeneous in strike with the major regional faults and are in good agreement with the regional direction of extension for this period. The characters of the turbiditic beds, with erosive base, graded bedding, and incomplete Bouma sequence, are in favour of a seismic origin. Instability structures, spineless synsedimentary faults and turbiditic inflows are thus considered as seismites and interpreted as the result of high seismicity periods including some events with M > 5 in the general extensive ambiance of the Liassic Tethyan rifting. The analysis of the geometrical relationships between all these sedimentary features allows to distinguish the successive stage of occurrence of an instability structure, from the sedimentation of alternating marls and limestones, and sudden turbiditic inflows, then early case-hardening of the turbidites, until the important seismotectonic event generating the spineless normal faults, themselves triggering the fall of indurated blocks and locally the forming of breccias. The Ornon Fault, which constitutes the border of the Taillefer block, 15 km eastward, played a major role during the Liassic sedimentation and may represent the major seismic fault related to the seismites occurrence in the Beaumont basin.  相似文献   

16.
松散沉积物中的断层常常没有留下明显的宏观形迹,单靠肉眼观测往往难以确定其存在,即使存在,也很难判定其活动性质和活动方式。最近,中国地震局地壳应力研究所和山西省地震局在太原市西张村横跨交城断裂开挖了大规模探槽,认为该探槽揭示了3次7级以上地震事件。文中通过对该探槽开展微观分析,来探索松散沉积物中宏观形迹不明的断层或隐形断层及其伴随的古地震事件的显微构造及显微沉积学标志。研究结果表明,该探槽中的断层在微观上表现为微破碎带、滑移面、变形条带和泥质充填带等多种形式,同时断层附近样品也有一定的变形现象。断层和外围样品中的碎屑颗粒在棱角度、粒度大小和分布特征等方面均有不同,断层样品粒度分布的分维值D=2.0。这些结果表明松散沉积物中断层作用有颗粒流动也有碎裂作用。同时发现了与震击物(seismite)宏观标志非常相似的诸多微观标志,如球状体、负荷构造、流体通道和物质流动等,从微观上证明该断裂活动伴随有古地震事件  相似文献   

17.
In this work we review earthquakes that happened in Southern Siberia and Mongolia within the coordinates of 42°–62° N and 80°–124° E and first propose relationships between earthquake parameters (a surface-wave earthquake magnitude M s and an epicentral intensity(I 0) based on the MSK-64 scale) and maximal distances from an earthquake epicenter (R e max), hypocenter (R h max), and a seismogenic fault (R f max) to the localities of secondary coseismic effects. Special attention was paid to the study of these relationships for the effects of soil liquefaction. Hence, it was shown that secondary deformations from an earthquake were distributed in space away from an earthquake epicenter, than from an associating seismogenic fault. The effects of soil liquefaction are manifested by several times closer to a seismogenic fault, than all other effects, regardless of the type of tectonic movement in a seismic focus. Within the 40 km zone from an earthquake epicenter 44% of the known manifestations of liquefaction process occurred; within the 40 km zone from a seismogenic fault—90%. We propose the next relationship for effects of soil liquefaction: M s = 0.007 × R e max + 5.168 that increases the limits of the maximum epicentral distance at an earthquake magnitude of 5.2 ≤ M s ≤ 8.1 as compared to the corresponding relationships for different regions of the world.  相似文献   

18.
The permeability of the Elkhorn fault zone,South Park,Colorado   总被引：5，自引：0，他引：5  
Marler J  Ge S 《Ground water》2003,41(3):321-332
The purposes of this study are to use both field and modeling approaches to characterize the permeability of a fault and to assess the role of the fault on regional ground water flow. The study subject is the Elkhorn fault, a low-angle reverse fault that brings Precambrian crystalline rocks over the sediments of Colorado's South Park Basin. The fault is hypothesized to act as a low-permeability barrier to flow, restricting interaction between the crystalline aquifer and the basin sediments. To test this hypothesis and to better predict the permeability structure of the fault, we synthesized geologic data to create a geologic model of the fault, conducted aquifer tests to estimate the hydrogeologic properties of the fault zone, and used ground water modeling to test the influence of a range of hydraulic properties for the fault zone on ground water flow in the region. Our study suggests that the fault is a low-permeability feature. Estimated heads are best matched to observations by modeling the fault as a 10-foot-thick interval of low-permeability fault gouge. Steady-state flow models show that much of the flow in the study area is topographically driven near land surface. Flow rates decrease with depth in the aquifers. In the footwall, ground water moves updip in the Michigan-San Isabel syncline to discharge in the South Park Basin. In the hanging wall, ground water moves east to a regional ground water divide. Sensitivity analyses indicate that hydraulic heads are most sensitive to changes in hydraulic conductivity and recharge.  相似文献   

19.
本文通过对长江三峡东段发震构造特征,新构造环境和深部构造条件等与地震活动相关性的分析给出了识别弱震区的地质构造标志。  相似文献   

20.
Studying subduction zone fluid at shallow seismogenic depths is important to understand the nature of fault rocks at the updip limit of the seismogenic zone because fluid–rock interactions affect heat and mass transfer, and fault strength. In this study, we conducted detailed analyses of distribution of shear veins, and estimation of pressure–temperature conditions for shear vein formation for the Yokonami mélange, Shikoku, Southwest Japan, which is tectonic mélange zone in an on‐land accretionary complex. We found a seismogenic fault at the upper boundary of the Yokonami mélange, indicating that the Yokonami mélange was active at seismogenic depth. The field‐transect distribution of shear veins was examined. The frequency, the total and mean thicknesses of the shear veins were about 3.7 per meter, about 10 mm per meter, and about 3 mm per shear vein, respectively. Quartz within the shear veins shows elongate‐blocky textures, suggesting precipitation from advective flow. The pressure and temperature conditions for shear vein formation were examined by fluid inclusion analysis, ranging 175–225°C and 143–215 MPa, respectively. The temperature is almost consistent with the paleotemperature determined from vitrinite reflectance, suggesting that the shear veins were formed at up to the maximum depth. The depth might be consistent with that where the seismogenic fault was formed. On the basis of the pressure and temperature conditions and the distribution of shear veins, we estimated the minimum volumetric ratio of fluid to host rocks, assuming that the shear veins had precipitated from advective flow. The estimated amount of fluid is about 106 m3 per cubic meter of host rocks. The results suggest that a large amount of fluid migrates through mélange zones at shallow seismogenic depths. This fluid possibly originates from the dehydration of clay minerals from underthrusted sediments and an altered subducting slab.  相似文献   

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