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1.
M Persaud  O.A Pfiffner   《Tectonophysics》2004,385(1-4):59-84
Post-glacial tectonic faults in the eastern Swiss Alps occur as single lineaments, clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend. The orientation of the faults reflects the underlying lithology and the pre-existing structures (joints, pervasive foliations) within these lithologies. Most post-glacially formed faults in the area around Chur, which undergoes active surface uplift of 1.6 mm/year, trend E–W and cut across Alpine and glacial features such as active screes and moraines. Additionally, there are NNW and ENE striking faults reactivating pervasive Alpine foliations and shear zones. Based on a comparison with the nodal planes of recent earthquakes, E–W striking faults are interpreted as active faults. Because of very short rupture lengths and mismatches of fault location with earthquake distribution, magnitude and abundance, the faults are considered to be secondary faults due to earthquake shaking, cumulative deformation in post- or interseismic periods or creep, and not primary earthquake-related faults. The maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission-track data and is therefore a long-lived feature that extends well into pre-glacial times. Isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern. Rather, the faults, earthquakes and surface uplift patterns suggest that the Alps are deforming under active compression and that the Aar massif basement uplift is still active in response to ongoing collision.  相似文献   

2.
The present kinematic and dynamic analysis of large-scale strike-slip faults, which enabled the formation of a collage of Altai terranes as a result of two collisional events. The Late Devonian–Early Carboniferous collision of the Gondwana-derived Altai-Mongolian terrane and the Siberian continent resulted in the formation of the Charysh–Terekta system of dextral strike-slip faults and later the Kurai and Kuznetsk–Teletsk–Bashkauss sinistral strike-slip faults. The Late Carboniferous–Permian collision of the Siberian and Kazakhstan continents resulted in the formation of the Chara, Irtysh and North-East sinistral strike-slip zones. The age of deformation of both collisional events becomes younger toward the inner areas of the Siberian continent. In the same direction the amount of displacement of strike-slip faulting decreases from several thousand to several hundred kilometers. The width of the Late Paleozoic zone of deformation reaches 1500 km. These events deformed the accretion-collision continental margins and their primary paleogeographic pattern.  相似文献   

3.
A statistical analysis was carried out to investigate spatial associations between natural seismicity and faults in southeastern Ontario and north-central New York State (between 73°18′ and 77°00′W and 43°30′ and 45°18′N). The study area is situated to the west of the seismically active St. Lawrence fault zone, and to the east of the Lake Ontario basin where recently documented geological and geophysical evidence points to possible neotectonic faulting. The weights of evidence method was used to judge the spatial associations between seismic events and populations of faults in eight arbitrarily defined orientation groups. Spatial analysis of data sets for seismic events in the periods 1930–1970 and post-1970 suggest stronger spatial associations between earthquake epicentres and faults with strikes that lie in the NW–SE quadrants, and weaker spatial associations of epicentres with faults that have strikes in the NE–SW quadrants. The strongest spatial associations were determined for groups of faults with strikes between 101° and 146°. The results suggest that faults striking broadly NW–SE, at high angles to the regional maximum horizontal compressive stress, are statistically more likely to be spatially associated with seismic events than faults striking broadly NE–SW. If the positive spatial associations can be interpreted as indicating genetic relationships between earthquakes and mapped faults, then the results may suggest that, as a population, NW–SE trending faults are more likely to be seismically active than NE–SW striking faults. Detailed geological studies of faults in the study area would be required to determine possible neotectonic displacements and the kinematics of the displacements.  相似文献   

4.
Two moderate magnitude earthquakes (M5.5 and M5.4) occurred in January 2010 with their epicenters at a distance of about 5?km between them, in the western part of the Corinth Gulf. The recordings of the regional seismological network, which is dense locally, were used for the location of the two main events and aftershocks, which are concentrated in three clusters beneath the northern coasts of the Gulf. The first two clusters accompany each one of the two stronger earthquakes, whereas the third cluster comprises only low magnitude aftershocks, located westward of the two stronger events. Seismic excitation started in January 18, 2010, with the M?=?5.5 earthquake in the area occupied by the central cluster. Seismicity immediately jumped to the east with numerous aftershocks and the M?=?5.4 earthquake which occurred four days later (January 22, 2010). Cross sections normal to the long axis of each cluster show ruptures on north dipping faults at depths of 7?C11?km. Focal mechanisms of the stronger events of the sequence support the results obtained from the spatial distribution of the aftershocks that three different fault segments activated in this excitation. The slip vectors of all the events have an NNW?CSSE to NNE?CSSW orientation almost parallel to the direction of extension along the Corinth Gulf. Calculation of the Coulomb stress changes supports an interaction between the different clusters, with the major activity being coincided with the area of positive induced stress changes after the first earthquake.  相似文献   

5.
Throughgoing fractures play a major role in subsurface fluid flow yet the kinematics of their formation, which directly impact rock flow properties, are often difficult to establish. We investigate throughgoing fractures in the Monterey Formation of California that developed by the coalescence of pre-existing joints. At Lompoc Landing, throughgoing fractures fall into three main groups: linked, linked with aperture, and breccia zones. The segmented nature of their walls provides numerous piercing points to firmly establish the sense of displacement. Analysis of displacement vectors derived from piercing points demonstrates that the NW–SE trending throughgoing fractures, often interpreted as strike–slip faults, are in fact extensional structures in origin. We suggest that this method may be applied to throughgoing fractures that form by the same mechanism in other geologic settings. Establishing kinematics of throughgoing fractures will lead to a better understanding of their contribution to subsurface fluid flow.  相似文献   

6.
Derek Rust   《Tectonophysics》2005,408(1-4):193
Transpressional tectonics are typically associated with restraining bends on major active strike-slip faults, resulting in uplift and steep terrain. This produces dynamic erosional and depositional conditions and difficulties for established lines of palaeoseismological investigation. Consequently, in these areas data are lacking to determine tectonic behaviour and future hazard potential along these important fault segments. The Big Bend of the San Andreas fault in the Transverse Ranges of southern California exemplifies these problems. However, landslides, probably seismically triggered, are widespread in the rugged terrain of the Big Bend. Fluvial reworking of these deposits rapidly produces geomorphic planes and lines that are markers for subsequent fault slip. The most useful are offset and abandoned stream channels, for these are relatively high precision markers for identifying individual faulting events. Palaeoseismological studies from the central Big Bend, involving 14C ages of charcoal fragments from trench exposures, illustrate these points and indicate that the past three faulting events, including the great 1857 earthquake, were relatively similar in scale, each producing offsets of about 7–7.5 m. The mean recurrence interval is 140–220 years. The pre-1857 event here may be the 1812 event documented south of the Big Bend or an event which took place probably between 1630 and 1690. Ground breakage in both events extended south of the Big Bend, unlike the 1857 event where rupture was skewed to the north. The preceding faulting event ruptured both to the north and south of the Big Bend and probably occurred between 1465 and 1495. All these events centred on the Big Bend and may be typical for this fault segment, suggesting that models of uniform long-term slip rates may not be applicable to the south-central San Andreas. A slip-rate estimate of 34–51 mm a− 1 for the central Big Bend, although uncertain, may also imply higher slip in the Big Bend and highlights difficulties in correlating slip-rates between sites with different tectonic settings. Slip rates on the San Andreas may increase within the broad compressional tectonics zone of the Big Bend, compared to the north and south where the plate boundary is a relatively linear and sub-parallel series of dominantly strike-slip faults. Partitioning slip within the Big Bend is inherently uncertain and insufficient suitably comparable data are available to sustain a uniform slip model, although such models are a common working assumption.  相似文献   

7.
An earthquake swarm occurred during February and March 1997 in the vicinity of the Tancitaro Volcano, in the southern part of the tectonically complex Michoacan Triangle. A study of these events provides an opportunity to map the active faults in the area and to learn if the orientation and the sense of motion on these faults are consistent with the mapped faults and the alignment of cinder cones in the region. The foci of 230 earthquakes, which could be located, are distributed between 10 and 18 km depth, and show an alignment in, roughly, a NE direction. The focal mechanisms and seismic moments of the 27 best-recorded events were determined by waveform modeling of P and S waves. These mechanisms show two distinct patterns. More than 50% of the solutions are left-lateral strike–slip mechanisms with a normal component. The preferred fault plane strikes NE. Another group of events, probably caused by triggered seismicity on the Chapala–Oaxaca fault zone, shows left-lateral strike–slip mechanisms with a large-thrust component on NW-trending faults. S wave splitting shows 1–2.5% crustal-anisotropy. The direction of the anisotropy coincides with the NE alignment of events, and the preferred nodal plane. This is also the alignment of cinder cones, suggesting that preexisting fractures and cracks are responsible for the seismicity and anisotropic behavior of the crust. The resulting stress orientation, NE compression, is the one expected for the fore-arc region. We conclude that although Michoacan Triangle lies in the Trans-Mexican Volcanic Belt, it does not form part of this stress province where the stress orientation is NS extension.  相似文献   

8.
In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo.The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map.The study area, during the Cenozoic, has been affected by five strike–slip tectonic events, which generated mainly strike–slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE–SW, E–W, NW–SE, N–S, and NNE–SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike–slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.  相似文献   

9.
Active faulting in the dead sea rift   总被引：8，自引：0，他引：8  
Manifestations of Late Quaternary and Holocene faulting were studied in a 500 km long segment of the Dead Sea transform (rift). Most prominent are left-slip faults, whose characteristic physiographic features are recognizable along most of the studied segment. Where these faults bend or are stepped to the left, rhomb-shaped grabens (or pull aparts) are produced, forming depressions. In the reverse situation compressional features such as pressure ridges, domes and folds form positive topographic features. Such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers. Normal faults, sub-parallel to the left slip faults, produce a trough-like valley along much of the Dead Sea transform, but are most prominent along the margins of the large rhomb-grabens, e.g., the Dead Sea trough. They apparently record a small component of transverse extension. Generally, their motion is slow: young slip did not occur along some segments during the last few 104 y. Elsewhere throws of 10–20 m at least occurred in this period. The Dead Sea transform is seismically active. The instrumental and historic records indicate a seismic slip rate of 0.15–0.35 cm/y during the last 1000–1500 y, while estimates of the average Pliocene—Pleistocene rate are 0.7–1.0 cm/y. Either much creep takes place, or the slip rate varies over periods of a few 103 y.  相似文献   

10.
The Lambert Glacier–Amery Ice Shelf occupies a narrow NNE–SSW-orientated fault-bound depression referred to as the Lambert Graben. Deep faults associated with this structure are recognised geophysically, and are interpreted to extend at least 700 km inland from the Antarctic coast. Kinematic and palaeostress data from quartz- and calcite-bearing faults, inferred to represent the surface expression of these deeper structures, suggest that a single faulting event occurred in response to NW–SE-directed extension, oblique to the axis of the graben. The bulk of the movement along these faults was dextral strike slip, accommodating components of both normal and reverse offset. In the northern Prince Charles Mountains, these faults disrupt the Permo-Triassic Amery Group and juxtapose it against Proterozoic basement. Equivalent strike-slip faults in the southern Prince Charles Mountains produce dextrally offset tectonic boundaries and metamorphic isogrades across the Lambert Glacier. The similarity in orientation between the palaeostress field calculated for these faults and the Cretaceous divergence vector between India and Antarctica strongly supports the inference that faulting was of Cretaceous age, and related to the break-up of Gondwana.  相似文献   

11.
The Castanhão reservoir was built in the state of Ceará, a dry region in Northeastern Brazil, to regulate the flow of the Jaguaribe River, for irrigation, and for power generation. It is an earth-filled dam, 60 m high, with a water capacity of 4.5 × 109 m3. The seismicity in the area has been monitored since 1998, with a few interruptions, using one analog or one digital station and, during a few periods, a three-station network. The first earthquakes likely to be induced events were detected in 2003, when the water level was about 20 m high. In early 2004 a very heavy rainfall season quickly filled the reservoir. Shortly after, an increase in the seismic activity occurred and many micro-earthquakes were recorded. We suggest that this activity resulted from an increase in pore pressure due to undrained response. Therefore, we may classify this cluster of micro-earthquakes as “initial seismicity.” We deployed a network with four analog stations in the area, following this activity, to determine the epicentral zone. At least three epicentral areas under the reservoir were detected. The spatio-temporal analysis of the available data revealed that the seismicity occurs in clusters and that these were activated at different periods. We identified four sets of faults (N–S-, E–W-, NW–SE-, and NE–SW-oriented), some of which moved in shallow crustal levels and as recently as the Quaternary (1.8 Ma). Under the present-day stress regime, the last two sets moved as strike-slip structures. We suggest a possible correlation between dormant faults and the observed induced seismicity.  相似文献   

12.
Seismic reflection and refraction data were collected west of New Zealand's South Island parallel to the Pacific–Australian Plate boundary. The obliquely convergent plate boundary is marked at the surface by the Alpine Fault, which juxtaposes continental crust of each plate. The data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary. Arrival times of wide-angle reflected and refracted events from 13 recording stations are used to construct a 380-km long crustal velocity model. The model shows that, beneath a 2–4-km thick sedimentary veneer, the crust consists of two layers. The upper layer velocities increase from 5.4–5.9 km/s at the top of the layer to 6.3 km/s at the base of the layer. The base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end. The lower layer velocities range from 6.3 to 7.1 km/s, and are commonly around 6.5 km/s at the top of the layer and 6.7 km/s at the base. Beneath the lower layer, the model has velocities of 8.2–8.5 km/s, typical of mantle material. The Mohorovicic discontinuity (Moho) therefore lies at the base of the second layer. It is at a depth of around 30 km but shallows over the south–central third of the profile to about 26 km, possibly associated with a southwest dipping detachment fault. The high, variable sub-Moho velocities of 8.2 km/s to 8.5 km/s are inferred to result from strong upper mantle anisotropy. Multichannel seismic reflection data cover about 220 km of the southern part of the modelled section. Beneath the well-layered Oligocene to recent sedimentary section, the crustal section is broadly divided into two zones, which correspond to the two layers of the velocity model. The upper layer (down to about 7–9 s two-way travel time) has few reflections. The lower layer (down to about 11 s two-way time) contains many strong, subparallel reflections. The base of this reflective zone is the Moho. Bi-vergent dipping reflective zones within this lower crustal layer are interpreted as interwedging structures common in areas of crustal shortening. These structures and the strong northeast dipping reflections beneath the Moho towards the north end of the (MCS) line are interpreted to be caused by Paleozoic north-dipping subduction and terrane collision at the margin of Gondwana. Deeper mantle reflections with variable dip are observed on the wide-angle gathers. Travel-time modelling of these events by ray-tracing through the established velocity model indicates depths of 50–110 km for these events. They show little coherence in dip and may be caused side-swipe from the adjacent crustal root under the Southern Alps or from the upper mantle density anomalies inferred from teleseismic data under the crustal root.  相似文献   

13.
U-series dating can be an effective means to obtain accurate and precise ages on Quaternary carbonates. However, most samples require a correction for U and Th in admixed detritus. This complication is often addressed through generation of U-Th isochrons, requiring analyses of several coeval samples. In addition, presence of water-derived (hydrogenous) Th in the carbonate can cause inaccuracies in isochron ages.This study reports a high-resolution U-series chronology of sediments deposited by Lake Lisan, the last glacial precursor of the Dead Sea. The strategy employed combines multiple measurements from a few stratigraphic heights and fewer analyses from many heights in a single described and measured section. The resulting chronology is based on ages at 22 heights in a ∼40-m-thick section covering the interval of ∼70-14 calendar ka BP. The effects of admixed detritus are evaluated using trace elements. Nearly pure aragonite samples, indicated by very low abundances of insoluble elements such as Nb and Zr, were found to contain hydrogenous Th, which causes the uncorrected U-230Th age of a modern sample to be ∼2.5 ka. Nevertheless, accurate ages have been obtained by correcting for the detrital and aqueous interferences. The resulting ages are in stratigraphic order, and their accuracy is evidenced by consistency of Lisan Formation U-series and 14C ages with the coral-based calendar-radiocarbon age calibration.The U-Th ages provide a context to unravel the limnological history of Lake Lisan. Boundaries between the Lower, Middle, and Upper stratigraphic units correspond to the MIS 4/3 and 3/2 transitions, respectively. During MIS 2 and 4 the lake generally showed a stable two-layer configuration and a positive fresh-water balance, reflected by deposition of laminated aragonite-detritus. Dry intervals during MIS 2 and 4 are indicated by thick gypsum layers and an inferred depositional hiatus, which are temporally associated with Heinrich events H1 at ∼17 ka and H6 at ∼65 ka, respectively. During MIS 3 the lake level was unstable with intermittent dry periods indicated by abundant clastic layers and a significant hiatus between ∼43-49 ka. Clastic layers are associated with Dansgaard-Oeschger events during MIS 3, and indicate lake level declines during abrupt Northern Hemisphere warmings. Overall, the climate of the Eastern Mediterranean region shows a strong linkage to the Northern Hemisphere climate, with increasing lake size and stability during cold periods, and fluctuations and dessication during warmings and Heinrich events.  相似文献   

14.
济阳坳陷早第三纪地震事件沉积序列   总被引：3，自引：0，他引：3       下载免费PDF全文
济阳坳陷下第三系沙河街组砂四段上部至砂三段地层中发育有以小规模阶梯状正断层为主、阶梯状正断层与振动扭曲变形构造为主和振动液化砂岩脉为主等3种垂向序列的震积岩.它们分别出现在盆地北部陡坡带、洼陷带和中央隆起带.震积岩的发育是控盆边界断裂强烈幕式活动导致的地震作用的直接结果,不同构造单元具有不同的震积序列,反映了随着距震中越来越远地震作用能量逐渐衰减的过程.根据震积岩发育的层位可以研究边界断裂强烈活动的时期,同时,震积岩在地层剖面中的重复出现表明了边界断裂活动具有周期性和幕式特征.  相似文献   

15.
再论震积岩及震积不整合——以川西-滇西地区为例   总被引：45，自引：1，他引：44  
梁定益  聂泽同 《地球科学》1994,19(6):845-850
震积岩是“灾变事件岩”的典型代表,震积岩一般由原地相的地震扰动层与上覆的滑来震积层组成,无论后者是否发育,震积不整合都是存在的。伸展构造环境下形成的区域性震积不整合,属于伸不整合,地震扰动层可以进一步分为软沉积及液化变形段,半固结变形的微褶皱和微断层段、脆性变形的震碎角砾岩段及韵律断层段等序列;群震型（多震旋回）剖面也可划分出出前震、主震、后震等序列。地震扰动序列对识别震积岩很关键,群震型剖面及化  相似文献   

16.
断裂的形成演化过程对油气的运聚成藏具有重要的影响。本文系统分析了呼和湖凹陷断裂特征、断裂演化及其与油气成藏的关系。研究表明,呼和湖凹陷以T_(22)和T_(04)反射层为界,划分为3套构造层,分别为下部伸展断陷构造层、中部断坳构造层,上部坳陷构造层,其中上部构造层中断裂不发育。纵向上主要发育了两套断裂系统,下部断裂系统展布方向主要是北东东向、北东向和北北东向。上部断裂系统展布方向主要为北北东向和北北西向。发育4种类型的断裂,分别为早期伸展断裂,中期走滑断裂,早期伸展中期走滑断裂和早期伸展中期走滑晚期反转断裂。断裂的主要形成时期为南屯组末期、伊敏组末期和青元岗组末期。断裂的形成和演化影响烃源岩的分布和热演化程度,形成多种类型的圈闭,为油气垂向运移提供良好的运移通道。其中在主力生油洼槽及其周边的几个控陷断层附近有利于油气富集。  相似文献   

17.
The central part of the Kamchatka Peninsula is characterized by a well defined depression associated with active volcanism, aligned NE–SW. On the east, the depression is bounded by a prominent system of active faults known as the East Kamchatka Fault Zone (EKFZ). In order to improve understanding of the behaviour and kinematic role of this fault zone a fieldwork programme, including study of trenches, was conducted in the north-central part of this system. Aerial photograph analysis, ground-truthed, indicates a westward fault dip with predominantly normal slip, while lateral offsets of river terraces and stream channels demonstrate a combined dextral component. Over 20 excavated pits and natural exposures were examined to confirm a detailed tephra succession extending from the early Holocene to recent historic eruptions. This chronological framework then provided age control on five past faulting events recognised in three trenches. These events took place at about 10.5, 6.0, 4.5 and, in a two-event succession within a short time span, at 3.3–3.2 ka BP. Event clustering may be characteristic and fault length–displacement values suggest earthquakes of M6.5, thus representing a significant new element in regional seismic hazard evaluations; additional to events generated at the subduction interface. The relatively long gap in faulting since the two most recent events may also be significant for hazard scenarios and there is a possible link between the faulting and volcanic activity in the depression. Overall, the EKFZ, together with the Nachiki Transverse Zone farther south, is thought to define a regional-scale block that is extending eastwards independently from the rest of Kamchatka.  相似文献   

18.
The benches and risers at Mormon Point, Death Valley, USA, have long been interpreted as strandlines cut by still-stands of pluvial lakes correlative with oxygen isotope stage (OIS) 5e/6 (120,000–186,000 yr B.P.) and OIS-2 (10,000–35,000 yr B.P.). This study presents geologic mapping and geomorphic analyses (Gilbert's criteria, longitudinal profiles), which indicate that only the highest bench at Mormon Point (90 m above mean sea level (msl)) is a lake strandline. The other prominent benches on the north-descending slope immediately below this strandline are interpreted as fault scarps offsetting a lacustrine abrasion platform. The faults offsetting the abrasion platform most likely join downward into and slip sympathetically with the Mormon Point turtleback fault, implying late Quaternary slip on this low-angle normal fault. Our geomorphic reinterpretation implies that the OIS-5e/6 lake receded rapidly enough not to cut strandlines and was 90 m deep. Consistent with independent core studies of the salt pan, no evidence of OIS-2 lake strandlines was found at Mormon Point, which indicates that the maximum elevation of the OIS-2 lake surface was −30 m msl. Thus, as measured by pluvial lake depth, the OIS-2 effective precipitation was significantly less than during OIS-5e/6, a finding that is more consistent with other studies in the region. The changed geomorphic context indicates that previous surface exposure dates on fault scarps and benches at Mormon Point are uninterpretable with respect to lake history.  相似文献   

19.
We found active faults in the fold and thrust belt between Tunglo town and the Tachia River in northwestern Taiwan. The surface rupture occurred in 1999 and 1935 nearby the study area, but no historical surface rupture is recorded in this area, suggesting that the seismic energy has been accumulated during the recent time. Deformed fluvial terraces aid in understanding late Quaternary tectonics in this tectonically active area. This area contains newly identified faults that we group as the Tunglo Fault System, which formed after the area's oldest fluvial terrace and appears at least 16 km long in roughly N–S orientation. Its progressive deformations are all recorded in associated terraces developed during the middle to late Quaternary. In the north, the system consists of two subparallel active faults, the Tunglo Fault and Tunglo East Fault, striking N–S and facing each other from opposite sides of the northward flowing Hsihu River, whose course may be controlled by interactions of above-mentioned two active faults. The northern part of the Tunglo Fault, to the west of the river, is a reverse fault with upthrown side on the west; conversely the Tunglo East Fault, to the east, is also a reverse fault, but with upthrown side on the east. Both faults are marked by a flexural scarp or eastward tilting of fluvial terraces. Considering a Quaternary syncline lies subparallel to the east of this fault system, the Tunglo Fault might be originated as a bending moment fault and the Tunglo East Fault as a flexural slip fault. However, they have developed as obvious reverse faults, which have progressive deformation under E–W compressive stress field of Taiwan. Farther south, a west-facing high scarp, the Tunglo South Fault, strikes NNE–SSW, oblique to the region's E–W direction of compression. Probably due to the strain partitioning, the Tunglo South Fault generates en echelon, elongated ridges and swales to accommodate right-lateral strike–slip displacement. Other structures in the area include eastward-striking portion of the Sanyi Fault, which has no evidence for late Quaternary surface rupture on this fault; perhaps slip on this part of Sanyi Fault ceased when the Tunglo Fault System became active.  相似文献   

20.
In southern Turkey ongoing differential impingement of Arabia into the weak Anatolian collisional collage resulting from subduction of the Neotethyan Ocean has produced one of the most complex crustal interactions along the Alpine–Himalayan Orogen. Several major transforms with disputed motions, including the northward extension of the Dead Sea Fault Zone (DSFZ), meet in this region. To evaluate neotectonic motion on the Amanos and East Hatay fault zones considered to be northward extensions of the DSFZ, the palaeomagnetism of volcanic fields in the Karasu Rift between these faults has been studied. Remanence carriers are low-Ti magnetites and all except 5 of 51 basalt lavas have normal polarity. Morphological, polarity and K–Ar evidence show that rift formation occurred largely during the Brunhes chron with volcanism concentrated at 0.66–0.35 Ma and a subsidiary episode at 0.25–0.05. Forty-four units of normal polarity yield a mean of D/I=8.8°/54.7° with inclination identical to the present-day field and declination rotated clockwise by 8.8±4.0°. Within the 15-km-wide Hassa sector of the Karasu Rift, the volcanic activity is concentrated between the Amanos and East Hatay faults, both with left lateral motions, which have rotated blocks bounded by NW–SE cross faults in a clockwise sense as the Arabian Block has moved northwestwards. An average lava age of 0.5 Ma yields a minimum cumulative slip rate on the system bounding faults of 0.46 cm/year according with the rate deduced from the Africa–Arabia Euler vector and reduced rates of slip on the southern extension of the DSFZ during Plio-Quaternary times. Estimates deduced from offsets of dated lavas flows and morphological features on the Amanos Fault Zone [Tectonophysics 344 (2002) 207] are lower (0.09–0.18 cm/year) probably because they are limited to surface fault breaks and do not embrace the seismogenic crust.Results of this study suggest that most strike slip on the DSFZ is taken up by the Amanos–East Hatay–Afrin fault array in southern Turkey. Comparable estimates of Quaternary slip rate are identified on other faults meeting at an unstable FFF junction (DSFZ, East Anatolian Fault Zone, Karatas Fault Zone). A deceleration in slip rate across the DSFZ and its northward continuation during Plio-Quaternary times correlates with reorganization of the tectonic regime during the last 1–3 Ma including tectonic escape within Anatolia, establishment of the North and East Anatolian Fault Zones bounding the Anatolian collage in mid–late Pliocene times, a contemporaneous transition from transpression to transtension and concentration of all basaltic magmatism in this region within the last 1 Ma.  相似文献   

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