The murdjadjo (Oran) geological structure which consists of an asymmetricfold has been studied. The anticline has a length of about 32 km and isN050 trending. Its relationship with the relatively high historical seismicityof the region is analysed. New critical investigations of contemporary documents enabled us to re-evaluate the December, 12, 1959(Ms = 4.7) and the May 12, 1889 (Ms = 4.6) earthquakes. Fieldobservations reveal the existence of a fault which affect the south-easternflank of the Murdjadjo anticline. The fault dips 60° to the NW andcut the tilted Neogene deposits which juxtaposes the Quaternary tilteddeposits. A NE-SW-trending direction of stream pattern underlies thefaulted flank of the anticline. Furthermore, offset of stream patternindicate a strike lateral slip component of the fault. Marine terracesmapped along the Oran coast indicates a uniform uplift rate of0.18 mm/yr which may be compared to the coseismic rate obtained inthe chelif region. Also, development of secondary small plain on theuplifted flank, the high subsidence in the Mleta quaternary plain whichjuxtaposes the faulted flank constitute evidence of recent tectonicmovements. The Murdjadjo fault, composed by two segments, mayproduce in the future strong earthquakes of magnitude equal or greaterthan 6.5. This fact suggests that the Oran earthquake of October 9, 1790(M = 7.5) which produced sea waves along the Spanish coast is likelygenerated by the Murdjadjo fault- related fold. Recurrence of earthquakedetermined on the basis of historical seismicity suggests a return period ofabout 1000 years for an earthquake of M = 7.3 which seem underestimatedcompared to the paleoseismic data available in The Tell atlas of Algeria. 相似文献
Where the Yellow River flows through the Haiyuan-Tongxin arc-form tectonic region on the northeastern side of the Qinghai-Xizang (Tibet) Plateau, as many as 10~21 basis and erosion terraces have been produced, among which the biggest altitude above river level is 401m and the formation age of the highest terrace is 1.57 Ma B.P. Based on comparative analysis of the Yellow River terraces located separately in the Mijiashan mountain, the Chemuxia gorge, the Heishanxia gorge and the other river terraces in the vast extent of the northern part of China, it has been found that the tectonic processes resulting in the formation of the terrace series is one of multi-gradational features, i.e., a terrace series can include the various terraces produced by tectonic uplifts of different scopes or scales and different ranks. The Yellow River terrace series in the study region can be divided into three grades. Among them, in the first grade there are 6 terraces which were formed separately at the same time in the vast extent of the northern part of China and represent the number and magnitude of uplift of the Qinghai-Xizang Plateau since 1.6 Ma B. P. ; in the second grade there are 5 terraces which were separately and simultaneously developed within the Haiyuan-Tianjingshan tectonic region and represent the number and magnitude of uplift of this tectonic region itself since 1.6Ma B. P.; in the third grade there are 10 terraces which developed on the eastern slope of the Mijiashan mountain and represent the number and amplitude of uplift of the Haiyuan tectonic belt itself since 1.6Ma B.P. Comparison of the terrace ages with loess-paleosoil sequence has also showed that the first grade terraces reflecting the vast scope uplifts of the Qinghai-Xizang Plateau are very comparable with climatic changes and their formation ages all correspond to the interglacial epochs during which paleosoils were formed. This implies that the vast extent tectonic uplifts resulting in river down-cutting are closely related to the warm-humid climatic periods which can also resnit in river downward erosion after strong dry and cold climatic periods, and they have jointly formed the tectonic-climatic cycles. There exists no unanimous and specific relationship between the formation ages of the second and third grade terraces and climatic changes and it is shown that the formation of those terraces was most mainly controlled by tectonic uplifts of the Tianjingshan block and the Haiyuan belt. The river terraces in the study region, therefore, may belong to 2 kinds of formation cause. One is a tectonic-climatic cyclical terrace produced jointly by vast extent tectonic uplifts and climatic changes, and the terraces of this kind are extensively distributed and can be well compared with each other among regions. Another is a pulse-tectonic cyclical terrace produced by local tectonic uplifts as dominant elements, and their distribution is restricted within an active belt and can not be compared with among regions. 相似文献
The Meuse River crosses the Feldbiss Fault Zone, one of the main border fault zones of the Roer Valley Graben in the southern part of the Netherlands. Uplift of the area south of the Feldbiss Fault Zone forced the Meuse River to incise and, as a result, a flight of terraces was formed. Faults of the Feldbiss Fault Zone have displaced the Middle and Late Pleistocene terrace deposits. In this study, an extensive geomorphological survey was carried out to locate the faults of the Feldbiss Fault Zone and to determine the displacement history of terrace deposits.The Feldbiss Fault Zone is characterized by an average displacement rate of 0.041–0.047 mm a−1 during the Late Pleistocene. Individual faults show an average displacement rate ranging between 0.010 and 0.034 mm a−1. The spatial variation in displacement rates along the individual faults reveals a system of overstepping faults. These normal faults developed by reactivation of Paleozoic strike-slip faults.As fault displacements at the bases of the younger terrace deposits are apparently similar to the tops of the adjacent older terrace, the age of these horizons is the same within thousands of years. This implies that the model of terrace development by rapid fluvial incision followed by slow aggradation does apply for this area. 相似文献
Topography of the terraced Danube Bend area indicates fast incision of the Danube River, which was followed by its tributaries dissecting deeply the former terrace levels. These surfaces are vertically bended along the river course, indicating antecedent incision of the Danube into the SW–NE trending Hungarian Mountain Range (HMR). Timing and rate of the incision of the Danube into the HMR and consequently, the rate of vertical motions have remained unresolved so far. This study aims at quantifying the landscape evolution and neotectonic deformation of the central part of the HMR. We used terrace levels along the antecedent section of the Danube River to constrain its incision rate, which is a measure for the uplift rate of the HMR.
Here we use 3He, a terrestrial in situ produced cosmogenic nuclide (TCN), to date uplifted geomorphologic levels along in the Danube Bend gorge. This method, first applied in the Carpathian–Pannonian system in the framework of present study, proved to be suitable for the quantification of landscape evolution in this area. Our 3He exposure age data suggest a maximum incision rate of 2.7 ± 0.1 mm/y for the last 170 ky. Considering likely effect of erosion a more conservative value of 1.6 mm/y for the last 270 ky, was obtained. Both rates are significantly higher than the incision rate of 0.41 mm/y of the Danube derived from previous geologic and geomorphic data for the last 360 ky. The formation of the terrace levels in the Danube Bend probably occurred during the last two glacial cycles (OIS 1–8). According to the exposure age data, there is no direct relationship between the terrace formation and climate in the Danube Bend. Incision of the Danube appears to be connected to the uplift of the HMR, obtained incision rate values can be taken as valid approximations of the uplift rate in the Danube Bend area. 相似文献
The New River crosses three physiogeologic provinces of the ancient, tectonically quiescent Appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late Cenozoic. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. We used cosmogenic 10Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, to constrain the timing of events in this history. 10Be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield model cosmogenic exposure ages of 130, 600, and 600–950 ka, respectively, but uncertainties on these ages are not well constrained. These results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by New River terrace deposits. The exposure ages yield a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 100 m/my. Modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m/my, in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m/my rates of surface erosion from ancient terrace remnants. Fluctuations between aggradation and rapid incision operate on timescales of 104− 105 year, similar to those of late Cenozoic climate variations, though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events. These second-order fluctuations appear within a longer-term signal of dominant aggradation (until 2 Ma) followed by dominant incision. A similar signal is observed on other Appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late Cenozoic. 相似文献
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