Evidence of positive tectonic inversion in the north-central sector of the Sicily Channel (Central Mediterranean)

In order to unravel the tectonic evolution of the north-central sector of the Sicily Channel (Central Mediterranean), a seismo-stratigraphic analysis of single- and multi-channel seismic reflection profiles has been carried out. This allowed to identify, between 20 and 50 km offshore the central-southern coast of Sicily, a ~80-km-long deformation belt, characterized by a set of WNW–ESE to NW–SE fault segments showing a poly-phasic activity. Within this belt, we observed: i) Miocene normal faults reactivated during Zanclean–Piacenzian time by dextral strike-slip motion, as a consequence of the Africa–Europe convergence; ii) releasing and restraining bend geometries forming well-developed pull-apart basins and compressive structures. In the central and western sectors of the belt, we identified local transpressional reactivations of Piacenzian time, attested by well-defined compressive features like push-up structures and fault-bend anticlines. The reconstruction of timing and style of tectonic deformation suggest a strike-slip reactivation of inherited normal faults and the local subsequent positive tectonic inversion, often documented along oblique thrust ramps. This pattern represents a key for an improved knowledge of the structural style of foreland fold-and-thrust belts propagating in a preexisting extensional domain. With regard to active tectonics and seismic hazards, recent GPS data and local seismicity events suggest that this deformation process could be still active and accomplished through deep-buried structures; moreover, several normal faults showing moderate displacements have been identified on top of the Madrepore Bank and Malta High, offsetting the Late Quaternary deposits. Finally, inside the northern part of the Gela Basin, multiple slope failures, originated during Pleistocene by the further advancing of the Gela Nappe, reveal tectonically induced potential instability processes.     

L'île Crémieu (Jura,France), un plateau calcaire épargné par la tectonique ?

The ‘Île Crémieu’, a plateau of Jurassic limestones located in the southern border of the Bresse and at the Jura front, is generally considered as non-deformed. Quaternary ice sheets and drainage have underlined and cleaned out some fracture planes trending NNE and NW–SE that border and crosscut the ‘Île Crémieu’. The analysis of seismic profiles reveals NNE-trending normal faults and NW–SE-trending strike-slip faults, crosscutting the basement to Late Miocene layers. Microtectonic fieldwork shows that these faults exist and were activated during the main Cainozoic tectonic events. To cite this article: M. Rocher et al., C. R. Geoscience 336 (2004).     

Evidence of positive tectonic inversion in the north-central sector of the Sicily Channel (Central Mediterranean)

In order to unravel the tectonic evolution of the north-central sector of the Sicily Channel (Central Mediterranean), a seismo-stratigraphic analysis of single- and multi-channel seismic reflection profiles has been carried out. This allowed to identify, between 20 and 50 km offshore the central-southern coast of Sicily, a ~80-km-long deformation belt, characterized by a set of WNW–ESE to NW–SE fault segments showing a poly-phasic activity. Within this belt, we observed: i) Miocene normal faults reactivated during Zanclean–Piacenzian time by dextral strike-slip motion, as a consequence of the Africa–Europe convergence; ii) releasing and restraining bend geometries forming well-developed pull-apart basins and compressive structures. In the central and western sectors of the belt, we identified local transpressional reactivations of Piacenzian time, attested by well-defined compressive features like push-up structures and fault-bend anticlines. The reconstruction of timing and style of tectonic deformation suggest a strike-slip reactivation of inherited normal faults and the local subsequent positive tectonic inversion, often documented along oblique thrust ramps. This pattern represents a key for an improved knowledge of the structural style of foreland fold-and-thrust belts propagating in a preexisting extensional domain. With regard to active tectonics and seismic hazards, recent GPS data and local seismicity events suggest that this deformation process could be still active and accomplished through deep-buried structures; moreover, several normal faults showing moderate displacements have been identified on top of the Madrepore Bank and Malta High, offsetting the Late Quaternary deposits. Finally, inside the northern part of the Gela Basin, multiple slope failures, originated during Pleistocene by the further advancing of the Gela Nappe, reveal tectonically induced potential instability processes.

     

Structural controls on the evolution of the Kutai Basin,East Kalimantan

The Kutai Basin formed in the middle Eocene as a result of extension linked to the opening of the Makassar Straits and Philippine Sea. Seismic profiles across the northern margin of the Kutai Basin show inverted middle Eocene half-graben oriented NNE–SSW and N–S. Field observations, geophysical data and computer modelling elucidate the evolution of one such inversion fold. NW–SE and NE–SW trending fractures and vein sets in the Cretaceous basement have been reactivated during the Tertiary. Offset of middle Eocene carbonate horizons and rapid syn-tectonic thickening of Upper Oligocene sediments on seismic sections indicate Late Oligocene extension on NW–SE trending en-echelon extensional faults. Early middle Miocene (N7–N8) inversion was concentrated on east-facing half-graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin. Slicken-fibre measurements indicate a shortening direction oriented 290°–310°. NE–SW faults were reactivated with a dominantly dextral transpressional sense of displacement. Faults oriented NW–SE were reactivated with both sinistral and dextral senses of movement, leading to the offset of fold axes above basement faults. The presence of dominantly WNW vergent thrusts indicates likely compression from the ESE. Initial extension during the middle Eocene was accommodated on NNE–SSW, N–S and NE–SW trending faults. Renewed extension on NW–SE trending faults during the late Oligocene occurred under a different kinematic regime, indicating a rotation of the extension direction by between 45° and 90°. Miocene collisions with the margins of northern and eastern Sundaland triggered the punctuated inversion of the basin. Inversion was concentrated in the weak continental crust underlying both the Kutai Basin and various Tertiary basins in Sulawesi whereas the stronger oceanic crust, or attenuated continental crust, underlying the Makassar Straits, acted as a passive conduit for compressional stresses.     

Modelling cover deformation and decoupling during inversion,using the Mid-Polish Trough as a case study

Seismic sections across the NW part of the Polish Basin show that thrust faults developed in the sedimentary units above the Zechstein evaporite layer during basin inversion. These cover thrust faults have formed above the basement footwall. Based on the evolution of the basin, a series of scaled analogue models was carried out to study interaction between a basement fault and cover sediments during basin extension and inversion. During model extension, a set of normal faults originated in the sand cover above the basement fault area. The distribution and geometry of these faults were dependent on the thickness of a ductile layer and pre-extension sand layer, synkinematic deposition, the amount of model extension, as well as on the presence of a ductile layer between the cover and basement. Footwall cover was faulted away from the basement only in cases where a large amount of model extension and hanging-wall subsidence were not balanced by synkinematic deposition. Model inversion reactivated major cover faults located above the basement fault tip as reverse faults, whereas other extensional faults were either rotated or activated only in their upper segments, evolving into sub-horizontal thrusts. New normal or reverse faults originated in the footwall cover in models which contained a very thin pre-extension sand layer above the ductile layer. This was also the case in the highly extended and shortened model in which synkinematic hanging-wall subsidence was not balanced by sand deposition during model extension. Model results show that inversion along the basement fault results in shortening of the cover units and formation of thrust faults. This scenario happens only when the cover units are decoupled from the basement by a ductile layer. Given this, we argue that the thrusts in the sedimentary infill of the Polish Basin, which are decoupled from the basement tectonics by Zechstein evaporites, developed due to the inversion of the basement faults during the Late Cretaceous-Early Tertiary.     

Mountain building processes in intracontinental oblique deformation belts: Lessons from the Gobi Corridor,Central Asia

This paper presents a review of the Quaternary–Recent deformation field and mountain building processes within the Gobi Corridor region of Central Asia, which includes the North Tibetan foreland, Beishan, Gobi Altai and easternmost Tien Shan. The region can be considered the ‘soft core’ of Central Asia which has been reactivated due to the continuing Indo-Eurasia collision to the south. Favourable preconditions for reactivation of Gobi Corridor basement include a mechanically weak Palaeozoic terrane collage sandwiched between rigid Precambrian basement blocks to the north and south, thermally weakened crust due to Jurassic–Miocene volcanism and widespread Palaeozoic–Mesozoic granitic magmatism with associated high radiogenic heat production, and crustal thinning due to widespread Cretaceous rift basin development. The network of Quaternary–Recent faults within the entire region defines a diffuse sinistral transpressional deformation field that has generated a transpressional basin and range physiographic province. Typically, thrust and oblique-slip thrust faults are WNW-striking and reactivate basement faults and fabrics, whereas left-lateral strike-slip faults are ENE-striking and cut across basement trends. The angular relationship between SHmax and pre-existing basement structural trends is the fundamental control on the kinematics of Late Cenozoic deformation. Along-strike and across-strike growth and coalescence of restraining bends, other transpressional ranges and thrust ridges is an important mountain building process. Thrust faults throughout the region are both NNE and SSW directed and thus there is no common structural vergence, nor orogenic foreland or hinterland. Root structures appear to be vertical faults, not low-angle decollements and flower structure fault geometries within individual ranges are common. Published earthquake and geodetic data are consistent with a diffusely deforming continental interior region with tectonic loading shared amongst a complex network of faults. Therefore, earthquake prediction is likely to be more complex than in plate boundary settings and extrapolation of derived Late Quaternary fault slip rates is not straightforward. Modern mountain building within the Gobi Corridor demonstrates that reactivation of ancient accretionary and collisional orogens within continental interiors can play an important role in continental evolution and the life cycle of orogenic belts.     

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.     

Seismogenic structures along continental convergent zones: from oblique subduction to mature collision

We summarize seismogenic structures in four regions of active convergence, each at a different stage of the collision process, with particular emphases on unusual, deep-seated seismogenic zones that were recently discovered. Along the eastern Hellenic arc near Crete, an additional seismogenic zone seems to occur below the seismogenic portion of the interplate thrust zone—a configuration found in several other oblique subduction zones that terminate laterally against collision belts. The unusual earthquakes show lateral compression, probably reflecting convergence between the subducting lithosphere's flank and the collision zone nearby. Along oblique zones of recent collision, the equivalence between space and time reveals the transition from subduction to full collision. In particular, intense seismicity beneath western Taiwan indicates that along the incipient zone of arc–continent collision, major earthquakes occur along high-angle reverse faults that reach deep into the crust or even the uppermost mantle. The seismogenic structures are likely to be reactivated normal faults on the passive continental margin of southeastern China. Since high-angle faults are ineffective in accommodating horizontal motion, it is not surprising that in the developed portion of the central Taiwan orogen (<5 Ma), seismogenic faulting occurs mainly along moderate-dipping (20–30°) thrusts. This is probably the only well-documented case of concurrent earthquake faulting on two major thrust faults, with the second seismogenic zone reaching down to depths of 30 km. Furthermore, the dual thrusts are out-of-sequence, being active in the hinterland of the deformation front. Along the mature Himalayan collision zone, where collision initiated about 50 Ma ago, current data are insufficient to distinguish whether most earthquakes occurred along multiple, out-of-sequence thrusts or along a major ramp thrust. Intriguingly, a very active seismic zone, including a large (M_w=6.7) earthquake in 1988, occurs at depths near 50 km beneath the foreland. Such a configuration may indicate the onset of a crustal nappe, involving the entire cratonic crust. In all cases of collision discussed here, the basal decollement, a key feature in the critical taper model of mountain building, appears to be aseismic. It seems that right at the onset of collision, earthquakes reflect reactivation of high-angle faults. For mature collision belts, earthquake faulting on moderate-dipping thrust accommodates a significant portion of convergence—a process involving the bulk of crust and possibly the uppermost mantle.     

Analysis of the stress regime and tectonic evolution of the Azerbaijan Plateau,Northwestern Iran

The increasing number of earthquakes in recent decades in Northwestern Iran and the determination of the epicenters of these events makes possible to estimate accurately the changing tectonic regime using the Win-Tensor inversion focal mechanism program. For this purpose focal mechanism data were collected from various sources, including the Centroid Moment Tensor catalog (CMT). The focal mechanism and fault slip data were analyzed to determine change in the stress field up to the present day. The results showed that two stages of brittle deformation occurred in the region. The first stage was related to Eocene compression in NE–SW direction, which created compressional structures with NW–SE strike, including the North and South Bozgush, south Ahar and Gushedagh thrust belts. The second brittle stage began in the Miocene with NW–SE compression and caused developing thrusts with N–S trends that were active presently. These stress regimes were created by the counter-clockwise rotation of the Azerbaijan plateau caused by movement on strike slip faults and continuous compression between the Arabian plate, the south Caspian basin and the Caucasus region. Pliocene-Quaternary activity of the Sabalan and Sahand volcanoes as well as recent earthquakes occurred as a result of this displacement and rotational movement. The abundance of hot springs in the Ardebil, Hero Abad and Bostanabad areas also bore witness to this activity.     

Tectonic stress pattern in the Chinese Mainland from the inversion of focal mechanism data

The tectonic stress pattern in the Chinese Mainland and kinematic models have been subjected to much debate. In the past several decades, several tectonic stress maps have been figured out; however, they generally suffer a poor time control. In the present study, 421 focal mechanism data up to January 2010 were compiled from the Global/Harvard CMT catalogue, and 396 of them were grouped into 23 distinct regions in function of geographic proximity. Reduced stress tensors were obtained from formal stress inversion for each region. The results indicated that, in the Chinese Mainland, the directions of maximum principal stress were ～NE–SW-trending in the northeastern region, ～NEE–SWW-trending in the North China region, ～N–S-trending in western Xinjiang, southern Tibet and the southern Yunnan region, ～NNE–SSW-trending in the northern Tibet and Qinghai region, ～NW–SE-trending in Gansu region, and ～E–W-trending in the western Sichuan region. The average tectonic stress regime was strike-slip faulting (SS) in the eastern Chinese Mainland and northern Tibet region, normal faulting (NF) in the southern Tibet, western Xinjiang and Yunnan region, and thrust faulting (TF) in most regions of Xinjiang, Qinghai and Gansu. The results of the present study combined with GPS velocities in the Chinese Mainland supported and could provide new insights into previous tectonic models (e.g., the extrusion model). From the perspective of tectonics, the mutual actions among the Eurasian plate, Pacific plate and Indian plate caused the present-day tectonic stress field in the Chinese Mainland.     

Seismic and field evidence for selective inversion of Cretaceous normal faults, Salta rift, northwest Argentina

Northwestern Argentina was the site of the continental Salta rift in Cretaceous to Paleogene time. The Salta rift had a complex geometry with several subbasins of different trends and subsidence patterns surrounding a central high. Fault trends in the rift were extremely variable. There is evidence of normal and/or transfer faults trending N, NE, E and SE. It is not clear if all these faults were active at the same time, indicating a poorly defined extension direction, or if they formed in different, non-coaxial extension phases. In either case, their trends were very likely influenced by preexisting fault systems. Beginning in early Eocene time, the rift basins were superseded by Andean foreland basins and later became caught in the Andean thrust deformation propagating eastward, resulting in the inversion of rift faults. Due to their different orientations, not all faults were equally prone to reactivation as thrusts. N to NNE trending faults were apparently most strongly inverted, probably often to a degree where the traces of their normal fault origin have become obliterated. We present seismic evidence of moderately inverted N trending faults in the Tres Cruces basin and field examples of preserved E trending normal faults. However, reactivation sometimes also affects faults trending approximately parallel to the main Neogene shortening direction, indicating short-term deviations from the general pattern of Neogene thrust deformation. These pulses of orogen-parallel contraction may be linked to the intermittent activity of oblique transfer zones.     

Timing of remanent magnetization acquisition in red beds: A case study from a syn-folding sedimentary basin

We propose to explain the origin of the double trend in seismicity of the Macas swarm in the Subandean Cordillera of Cutucú (Ecuador) and characterize the corresponding active deformation of that region. For that purpose, seismological and geological data have been used, with the deployment of a temporary seismological array, with geological field observations and image processing. We found that some earthquakes are aligned on a well known NNE–SSW trend corresponding to the orientation of the nodal planes of the reverse focal mechanism of the M_w=7.0 1995 Macas earthquake as for its aftershocks. Nevertheless, many smaller events are aligned on an unexpected NNW–SSE trend inside the Cutucú Cordillera. We interpret these two orientations of the Macas swarm as linked to Subandean basement thrusts inherited from the inversion tectonics of a NNE–SSW trending Triassic–Jurassic rift, which has been uplifted and partly extruded in the Cutucú Cordillera. The present partitioning of this part of the Subandean deformation is controlled by pre-existing NNE–SSW to NNW–SSE Triassic–Jurassic normal faults that have been subsequently compressed–transpressed and reactivated into reverse faults. Major boundary faults of the rift were NNE–SSW oriented and correspond now to some main Subandean thrusts as confirms the focal mechanism of the 1995 main shock located on the eastern border (Morona frontal thrust) and the orientation of its aftershocks. In the Cutucú Cordillera, the double orientation of present swarm can be interpreted as the result of accommodation of deformation along NNW–SSE pre-existing faults inside the inverted rift system, linked to the motion of the Morona frontal NNE–SSW thrust.     

Déformations néogènes et quaternaires de la bordure nord haut atlasique (Maroc): rôle du socle et consequences structurales

According to major discontinuities, continental deposits in the Cenozoic Atlas basins are subdivided into three groups (pre-, syn- and post-tectonic). Progressive unconformities are the main characteristic of the syntectonic formations, implying that the Atlas tectonic episode is synchronous with Neogene and Quaternary sedimentation. This tectonic episode is responsible for the inversion of Early Mesozoic extensional structures within the basement, which were reactivated into symmetrical thrusts or transpressional faults. Shortening of the basement induced the detachment of the cover. Deformation of the cover is expressed by thrust faults (with southern and northern vergences), folds and flexures linked to blind thrusts. Kinematic data show that the main regional compression was directed N150 ± 10° during the Neogene and north-south during the Quaternary. The involvement of the upper crust, in the Alpine Atlasic Belt, contributed to create areas of high relief. The High Atlas can be interpreted as resulting from large Cenozoic thrusts, and compared with the Pyrenean Axial Zone, although their pre-Cenozoic histories can differ markedly.     

New insights on the tectonic and paleogeographic evolution of the central Atlasic domain of Tunisia

Geological and geoseismic profiles and well data gathered with field observations from the Atlasic Chain in central Tunisia highlight folded structures, tectonic events, and significant faults. These events controlled basin formation and evolution during successive Mesozoic extensional phases, followed by the tectonic inversion during the Atlasic Orogeny known on a Tethyan scale. The Cretaceous extension is well recorded through deposition, which supplied the normal faults system and influenced sediment distribution and regional subsidence. The major event is the normal slip of the principle inherited fault during the Cretaceous subsidence. The northwestern blocks, which are north of the faults of Mrhila–Trozza–Cherichira and Ballouta and west of the NS axis, correspond to continually subsiding areas of the Upper Cretaceous series. Subsequent faulting reactivated compressional structures such as strike-slips, reverse, and thrust faults during the Tertiary Orogeny which largely affected the Tunisian Atlasic domain. Geological profiles point out the evidence of the Upper Cretaceous emersion of the central Tunisia domain and lateral thickness variation of the series from Jurassic to Quaternary, unconformities, and halokinesis movement.     

CROSS-SECTIONS OF THE WESTERN HIMALAYAN FOOTHILLS:PROBLEMS IN RESTORATION AND IMPLICATIONS FOR CRUSTAL SHORTENING

CROSS-SECTIONS OF THE WESTERN HIMALAYAN FOOTHILLS:PROBLEMS IN RESTORATION AND IMPLICATIONS FOR CRUSTAL SHORTENING1　PowersPM ,LillieRJ ,YeatsRS .StructureandshorteningoftheKangraandDehraDunreentrants ,Sub Himalaya ,India[J].GSABulletin ,1998,110 :10 10～ 10 2 7.…     

Modelling the interseismic deformation of a thrust system: seismogenic potential of the Southern Alps

This article focuses on the Montello thrust system in the Eastern Southern Alps as a potential seismogenic source. This system is of particular interest because of its lack of historical seismicity. Nevertheless, the system is undergoing active deformation. We developed a finite‐element model using visco‐elasto‐plastic rheology. The free parameters of the model (essentially, the locking status of the three thrusts included in the study), were constrained by matching the observed horizontal GPS and vertical levelling data. We show that the amount of interseismic fault locking, and thus the seismic potential, is not necessarily associated with the fastest‐slipping faults. More specifically, the locked Bassano thrust has a greater seismic potential than the freely slipping Montello thrust. The findings suggest that faults with subtle evidence of Quaternary activity should be carefully considered when creating seismic hazard maps.     

Tectonics of the Northern Bresse region (France) during the Alpine cycle

Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE–SW, E–W and NW–SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N–S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE–SW in the graben. After a transitional minor E–W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE–SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE–SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.     

塔里木盆地巴楚隆起北缘的吐木休克断裂与巴东断裂

吐木休克断裂位于塔里木盆地西部,巴楚隆起和阿瓦提凹陷之间,是一条大型基底卷入型冲断构造。走向NW‐SE,呈弧形向NEE凸出;倾向巴楚隆起。根据构造变形特征,断裂自NW向SE可以划分为4段。Ⅰ和Ⅲ段为简单基底卷入型冲断构造段;Ⅱ段发育背冲断层,与主干断层呈“y”字型剖面组合关系;Ⅳ段为基底卷入型楔状构造,主冲断层顶部出现一条向巴楚隆起逆冲的反冲断层。断裂上盘发育背斜,下盘有明显的“牵引构造”,显示吐木休克断裂可能是由吐木休克背斜北翼突破形成的,是一条褶皱相关断层。吐木休克断裂形成于中新世晚期至上新世初,持续演化至第四纪。断裂带上发育的上新世末—第四纪初正断层代表印度—亚洲碰撞脉动式远程效应的一个构造间歇期。吐木休克断裂东侧的巴东断裂是巴楚隆起与塔中隆起的过渡构造带,雏形形成于奥陶纪晚期—志留纪,晚新生代复活。     

Basin inversion by distributed deformation: the southern margin of the Bristol Channel Basin, England

Several models of basin inversion described in the literature are tested in a study of Triassic and Early Jurassic strata exposed along the southern margin of the Bristol Channel Basin in Somerset, England that has been exhumed by <3 km. Two key features of the superbly exposed normal faults are that they formed at several times during basin evolution—not during Triassic to Early Jurassic growth, but during Late Jurassic rifting, and during and after inversion; and that >95% of them are still in net extension, despite widespread kinematic evidence for reverse reactivation. When coupled with the general absence of thin-skinned thrusts and the widespread occurrence of regional contractional folds, it appears that none of three main inversion models—the fault-reactivation model, the thin-skinned model and the buttress model—are by themselves applicable. We erect a new model of basin inversion, the distributed deformation model, which consists of three stages of basin inversion. Stage one involved early partial reactivation of large-displacement steep normal faults. Stage two was dominated by folding, wherein fault blocks underwent oblique (non-coaxial) shortening by map scale folding, accompanied by formation of outer arc normal faults, minor cleavage and neoformed thrusts. Stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike-slip faults that partitioned deformation into compartments.     

Triggered seismicity in the Andean arc region via static stress variation by the MW = 8.8, February 27, 2010, Maule earthquake

We localized crustal earthquakes in the Andean arc, between 35°S and 36°S, from December 2009 to May 2010. This research shows a seismicity increase, in a narrow longitudinal area, of more than nine times after the great M_w 8.8 Maule earthquake.The localized seismicity defines an area of ∼80 km long and ∼18 km wide and NNW to NNE trend. The M_d magnitudes varied from 0.7 to 3.1 except for two earthquakes with M_w of 3.9 and 4.5, located in the northern end of the area. The focal mechanisms for these two last events were normal/strike-slip and strike-slip respectively.During 2011, a network of 13 temporary stations was installed in the trasarc region in Malargüe, Argentina. Sixty earthquakes were localized in the study region during an 8 month period.We explored how changes in Coulomb conditions associated with the mega-thrust earthquake triggered subsequent upper-plate events in the arc region. We assumed the major proposed structures as receiver faults and used previously published earthquake source parameters and slip distribution for the Maule quake. The largest contribution to static stress change, up to 5 bars, derives from unclamping resulting consistent with co-seismic dilatational deformation inferred from GPS observations in the region and subsidence in nearby volcanoes caused by magma migration.Three different Quaternary tectonic settings–extensional, strike-slip and compressional-have been proposed for the arc region at these latitudes. We found that the unclamping produced by the Maule quake could temporarily change the local regime to normal/strike-slip, or at least it would favor the activation of Quaternary NNE to N-trending dextral strike-slip faults with dextral transtensional movement.