Present-day stress orientations in the Great Sumatran Fault in North Sumatra
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Trench-parallel strike slip faults develop at lithospheric scale during oblique high-angle subduction. A “sliver” plate forms due to slip partitioning between the subduction plane (margin-normal slip) and the strike slip fault (margin-parallel slip). This process ultimately controls the location of volcanoes and earthquakes. The Great Sumatran Fault (GSF) is a showcase of this tectonic configuration located in the Sumatran section of the Sunda arc-trench system. Kinematics of the large-scale structures of the Sumatra section of the Sunda trench are well understood and tensional and compressional domains have been identified at the regional scale. However, detailed understanding of the stress distribution is still lacking yet essential for evaluating the seismic hazard potential in order to mitigate the impact of the large, hazardous earthquakes associated with this system.In this contribution, we study the present-day stress orientations of the Great Sumatran Fault at its northern section (NGSF). We deduced the state of (paleo)stress along structural features observed at two scales; (a) at meso-scale, analyzing ASTER GDEM data, and (b) at outcrop-scale, with field data measurements. We focus on the leading edge of northwestward propagating continental sliver deformation exposed on land, i.e. the northernmost tip of Sumatra (between 4,5°N and 6°N), where the NGSF bifurcates into its two major branches. These two fault branches form two structural highs bounding a graben basin in the onshore, continuing into the Pulau Weh Island in the east, and the Pulau Aceh Archipelago in the west. Given their location at the present day deformation front, these islands provide a unique opportunity to compare the sub-recent stress field with present day stresses, contributing to the understanding of the stress field evolution during northwestwards propagation of the Sumatran forearc continental sliver.Keywords:
Stress field
Transtension
Abstract Structural data and a regional tectonic interpretation are given for the NE–SW-trending Hatay Graben, southern Turkey, within the collision zone of the African (Arabian) and Eurasian (Anatolian) plates. Regional GPS and seismicity data are used to shed light on the recent tectonic development of the Hatay Graben. Faults within Upper Cretaceous to Quaternary sediments are categorized as of first-, second- and third-order type, depending on their scale, location and character. Normal, oblique and strike-slip faults predominate throughout the area.The flanks of the graben are dominated by normal faults, mainly striking parallel to the graben, that is, 045–225°. In contrast, the graben axis exhibits strike-slip faults, trending 100–200°, together with normal faults striking 040–060° and 150–190° (a subset strikes 110–130°). Similarly orientated normal faults occur throughout Upper Cretaceous to Pliocene sediments, whereas strike-slip faults are mostly within Pliocene sediments near the graben axis. Stress inversion of slickenline data from mostly Pliocene sediments at ten suitable locations (all near the graben axis) show that σ 3 directions (minimum stress axis ≈ extension direction) are uniform in the northeast of the graben but orientated at a high angle to the graben margins. More variable σ 3 directions in the southwest may reflect local block rotations. During Miocene times, the Arabian and Anatolian plates collided, forming a foreland basin associated with flexurally controlled normal faulting. During the Late Miocene there was a transition from extension to transtension (oblique extension). The neotectonic Hatay Graben formed during the Plio-Quaternary in a transtensional setting. In the light of modern and ancient comparisons, it is suggested that contemporaneous strain was compartmentalized into large-scale normal faults on the graben margins and mainly small-scale strike-slip faults near the graben axis. Overall, the graben reflects Plio-Quaternary westward tectonic escape from a collision zone towards the east to a pre- or syn-collisional zone to the west in the Mediterranean Sea.
Horst and graben
Transtension
Neogene
Half-graben
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Transtension
Transpression
Transform fault
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The Yingxiong Range is the largest anticlinal belt within the triangular overlapping zone between the Altyn Tagh Fault and the Eastern Kunlun Fault and thus records the critical information concerning the strike-slip superimposition between the two large-scale left-slip faults. The detailed structural analysis on the basis of 3D seismic data shows that the Shizigou (SZG) and Youshashan (YSS) structures in the Yingxiong Range are controlled by NE-dipping low-angle thrust faults at shallow depth and three groups of faults including the NW-striking inverted faults, the WNW-striking XI fault and the N–S-striking Shidong fault zone at deep levels. The inverted faults were right-stepping en-échelon sinistral transtensional normal faults in the Eocene. Fracture analysis on cores of the U. Xiaganchaigou Formation shows the existence of syn-sedimentary normal faults which indicate Eocene extension deformation in the Yingxiong Range. The Eocene transtensional normal faults constituted a half-graben structural system and controlled the formation of the SZG sag. In the early Miocene, the XI fault obliquely superimposed the pre-existing Eocene transtensional normal faults, causing the reactivation of these faults in a reverse sense. Simultaneously, the Shidong fault zone started to develop as a dextral tear fault. The oblique strike-slip superimposition from transtension to transpression in the Yingxiong Range reflects the differential controlling effects of the asynchronous initiation of the Altyn Tagh Fault and the Eastern Kunlun Fault on the structural evolution and oil-gas reservoir development in the western Qaidam Basin.
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Echelon formation
Transpression
Thrust fault
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The change of motion mode of multistage active strike-slip faults controls the segmentary types of strike-slip faults, which is seldom studied.Based on high-precision 3D seismic data and the principle of structural analysis, this paper defines the structural evolution characteristics of the tp12cx strike-slip fault in the key structural period and identifies the fault segmentation types. Combined with the statistical results of drilling production data and fault width, and fault width, it is demonstrated that different fault segments display various reservoir architecture and hydrocarbon potential. The tp12cx strike-slip fault experienced two phases of tectonic activity controlling reservoir development: the middle Caledonian and the late Caledonian to early Hercynian. During the middle Caledonian period, a left-lateral and left-step strike-slip fault was formed. The overlapping segments of the left steps were transtension zones, and the rest were pure strike-slip segments. From the late Caledonian to the early Hercynian, the movement mode changed from left-lateral to right-lateral, and the arrangement of left steps remained unchanged, forming right-lateral and left-step strike-slip faults. That is, as a weak zone, the transtension zones of all the preexisting overlapping segments took the lead in moving into many pure strike-slip segments and maintained the transtensional property. During the right-lateral slipping process of all the original pure strike-slip segments along the fault, they were blocked and squeezed by the surrounding rocks on both sides, forming a series of “positive” flower-shaped fault anticlines, which became overlapping segments, and the fault property became transpressional. Under the continuous action of the right-lateral slipping, a regional right-lateral and right-step strike slip fault formed. The interiors of the right-step-arranged faults were composed of the left-step arranged faults. Among them, the right-step overlapping segments were weakly step overlapping segments were weakly transtensional, and the larger the fault width of the internal left step pure strike slip and overlapping segments, the stronger the dissolution. The deformation of the right-step pure strike-slip segments was weak and basically maintained the characteristics of the previous stage. According to the evolution and superposition of pure strike-slipped and overlapped segments and the changes in fault properties, four types of strike-slip fault segments and corresponding reservoir models are divided. Type I: left-step pure strike-slip segment + left-step transpressional segment + right-step transtensional segment; Type II: left-step transtensional segment + left-step pure strike-slip segment + right-step transtensional segment; Type III: left-step pure strike-slip segment + left-step transpressional segment; and Type IV: left-step transtensional segment + left-step pure strike-slip segment. The fault width and oil production of type II and type IV with transtensional properties are much larger than those of type I and type III with transpressional properties.
Transtension
Slipping
Transpression
Pull apart basin
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Transtension
Transpression
Stress field
Seismotectonics
Eurasian Plate
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Transtension
Echelon formation
Transpression
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Lying in the east of Heilongjiang province, Yishu graben is a Cenozoic fault basin comprising two large second-class structural units, i.e., Tangyuan and Fangzheng fault basins. As a result, the structural study of the two units can help to find out the processes of formation and evolution of Yishu graben. Our results show that the activity of the boundary faults of Yishu graben is characterized by multiple centers and imbalance in Eocene-Oligocene epoch. The fault at the east boundary of Tangyuan fault basin is a basin-controlling fault, and the faults at both the east and the west boundaries of Fangzheng fault basin are also a basin-controlling fault, with the west boundary fault at Fangzheng being the major one. Analysis of the fault growth index shows that the NW fault within the graben is identical with the boundary fault in activity, and the two faults both serve to regulate the evolution and development of the boundary faults, and it was found that the transtension direction of the boundary faults of Yishu graben was determined by the Moho gradient tilt direction, since the latter is identical to the extension direction of the graben as a whole.
Transtension
Horst and graben
Half-graben
Paleogene
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Oblique continent—continent collision between Iranian microcontinent and Arabian plate is the main cause of transpression and transtension regimes in this area. Zagros orogeny in this area resulted in formation of various structures including thrust fault-related folds, dextral and sinistral, strike slip faults, normal fault related to dextral strike slip fault. Thrust faults within the area under study are duplex with general trend of NW-SE and dip toward the north-east with right slip component. Strike slip fault regime acts as tear fault and it is active yet. Therefore, simultaneous presence of thrusts and strike slip faults illustrates convergent dextral transpressional tectonic regime while this transpressional regime accompanied with transtension as well; since normal faults are also seen in alluvium around depression of Sirjan which can be as a result of extension stresses due to strike slip faults activity of the district. The results achieved from geometry and kinematic analysis of west of Sirjan structures indicate that structures of the area have characteristics of internal part of Zagros orogeny.
Transtension
Transpression
Orogeny
Alpine orogeny
Lineament
Pull apart basin
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