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The mechanical interaction of propagating normal faults is known to influence the linkage geometry of first-order faults, and the development of second-order faults and fractures, which transfer displacement within relay zones. Natural examples of growth faults from two active volcanic rift zones (Koa’e, Big Island, Hawaii and Krafla, northern Iceland) illustrate the importance of relay zone heave gradients and associated vertical axis rotations in evolving continental rift systems. Detailed field mapping of deformation within two relay zones, located at the tips of en echelon rift faults, reveals pronounced heave displacement deficits that are accommodated by: (1) extensional-shear faults that strike at a low angle ( 45°) and accommodate a significant component of rift zone-parallel extension. Such extension parallel to the rift axis may oppose any shear-induced shortening that is typically required for vertical axis rotations (e.g. bookshelf faulting models). At the surface, this volume increase is accommodated by open fractures, but may be accommodated in the subsurface by veins or dikes oriented oblique- and normal to the rift axis. This proposal is consistent with data from exhumed contemporaneous fault and dike systems seen on the Faroe Islands and in Kangerlussuaq (East Greenland). Based on the findings presented here we propose a new conceptual model for the evolution of segmented continental rift basins on the NE Atlantic margins.

Qena-Safaga road, which is one of the vital transportation lines in south of Egypt, is affected by a set of recent NE-SW to ENE-WSW vertical tensile and en echelon fractures. These fractures are distributed for about 12 km along both sides of the road and constitute a major threat to the infrastructure and environment. Some studies suggested the tectonic origin of these fractures while others suggested that they were formed due to geotechnical problems in the shallow subsurface soil. In order to study the nature and distribution of these fractures in the subsurface, low cost seismic surveys were conducted at the area of KM 22 of Qena-Safaga road. Eleven shallow seismic refraction lines as well as three MASW lines were acquired. The seismic refraction data were analyzed using tomographic methods to produce 2D velocity-depth models. To estimate the near surface seismic properties such as Vp/Vs and Poisson’s ratio that are important for the geologic interpretation of the data, MASW data where analyzed to obtain 1D shear wave velocity models. 3D images including 3D volume, fence diagram and depth slices were also produced to study the vertical and lateral variation of the P-wave velocity. In the resulted 2D tomographic models, three seismic units were deduced. The first unit represents the thin weathered surface layer having P-wave velocities of 300–700 m/s. The second unit has P-wave velocities of 700–1600 m/s and S-wave velocities of 281–926 m/s. It may represent the marl unit of Pliocene Durri Formation. Its thickness ranges from 11.8 m to 30 m. The bedrock was deduced to be at depths from 13 to 40 m and is characterized by velocities greater than 1600 m/s. The fractures were traced down to the bedrock along the seismic sections. The variable thickness of the marl unit as well as the variable depths of the bedrock were deduced to be resulting from the effect of subsurface.

The Dawn Science Team is conducting a geological mapping campaign at Ceres during the nominal mission, including iterative mapping using data obtained during each orbital phase. We are using geological mapping as a method to identify the geologic processes that have modified the surface of dwarf planet Ceres. We here present the geology of the Ac-9 Occator quadrangle, located between 22˚S-22˚N and 216-288˚E. The Ac-9 map area is within the topographically high region named Hanami Planum. Features of note within the profile include impact craters Occator, Azacca, Lociyo, Nepen and Kirnis. Four of these craters have fractured, shallow floors, morphometrically comparable to floor-fractured craters (FFCs) on the Moon. Similar to models for the formation of the lunar FFCs, we suggest that these Ceres FFCs are a result of cryomagmatic uplift under the crater floors. A set of regional linear structures called the Samhain Catenae do not have any obvious relationship to impact craters. Many of the catenae are comprised of smaller structures that have linked together, suggestive of en echelon fractures. It has been suggested that these fractures formed due to the uplift of Hanami Planum due to cryromagmatic plumes.

Using a 2D and 3D seismic dataset and four exploration wells, we have mapped the Lower Cretaceous interval within the ENE-WNW-striking Swaen Graben in the Barents Sea in order to characterize the presence of clastic wedges and improve the paleogeographic understanding and the depositional role of the graben during this period. A few Lower Cretaceous clastic wedges have been interpreted within the Graben. Four master faults, two of them striking to the west and two striking northeast creating en echelon pattern, control the distribution of the wedges, which are thickest closed to the faults and become thinner toward the Graben center. On the western part of the Graben, a possible transportation path was changing over time, infilling from south to north and then in the opposite direction. While on the eastern part, the wedges are located on both sides. It is suggested that the graben acted as a very shallow and local depocenter and it did not affect the regional paleogeography.

A considerable part of the seismic risk to the capital area of Iceland is provided by a series of strike-slip faults at the mid-Atlantic plate boundary within a distance range of 15–35 km. About two thirds of the Icelandic population lives within this distance range from the source areas of M 6–6.5 earthquakes. The structure of the plate boundaries in SW-Iceland is relatively complex. Three branches meet in the Hengill Triple Junction, the oblique rift of the Reykjanes Peninsula, the South Iceland Seismic Zone (a transform zone) and the Western Volcanic Zone (a rift zone). The Reykjanes Peninsula oblique rift has an over-all trend of 70°, highly oblique with respect to the spreading direction, 101° in this region. It contains both volcanic systems and seismogenic strike-slip faults. The fissure swarms of individual volcanic systems contain normal faults and fissures, with a NE-trend, also quite oblique to the plate boundary. The fissure swarms fade out towards the NE and SW as they extend into the plates on either side. Overprinting this pattern of volcano-tectonic structures are sets of parallel, northerly striking transcurrent faults that generate the largest earthquakes in this zone. Their surface expressions are en echelon fracture arrays and push-up structures. The sense of displacement is right-lateral. In the 15 km long section of the rift studied here we find evidence for at least six faults of this type. The length of individual faults may exceed 12 km. The distance between them varies from 1 to 5 km, and together they form a bookshelf-type fault system taking up the left-lateral component of plate movements across the oblique rift zone.

En-echelon veins are a set of tensile fractures that develop during the initiation of shear zones under certain conditions, but factors that control fracture patterns remain unclear. In this study, we performed numerical simulations using the two-dimensional distinct element method to understand the influence of effective normal stress on the development of fractures during shear deformation. At low effective normal stress (10 MPa), dilation takes place at an angle of ≈40°–45° to the shear boundary, and en-echelon arrays of tensile fractures develop. In contrast, at high effective normal stress (150 MPa), en-echelon veins are not developed, but a distinct shear plane forms. A transient behavior characterizes intermediate effective normal stress (≈50 MPa): early tensile cracks are generated and then propagate to form larger brittle faults. In this case, the larger strain energy released in the later stage is due to the greater shear strength. Under crustal conditions, effective normal stress varies, due to the change in fluid pressure. Our results suggest that en-echelon veins are indicators of high fluid pressure, close to lithostatic conditions, i.e. effective normal stress close to zero, and that a transition of the failure mode from tensile to shear could occur in response to a dynamic change of fluid pressure during fracturing.

Quartz veins from a subhorizontal shear zone in the Kodiak accretionary complex in southwest Alaska record cycles of cracking and sealing contemporaneous with simple shear, and analysis of the vein array in the context of silica dissolution, diffusion, and precipitation leads to the conclusion that the time needed to seal after a fracture event overlaps with the time scales associated with the recurrence of slip instabilities along active megathrusts. The central belt of the Kodiak accretionary complex is interpreted as a shear zone developed adjacent to a paleo-decollement that was active in the Late Cretaceous based on large strain magnitudes, recumbent isoclinal folds, and regional cleavage patterns that depict rotation of the steep cleavage that characterizes most of the Kodiak Formation into the horizontal fabrics of the central belt. Within this regional shear zone, crack-seal veins composed of quartz with phyllosilicate inclusion bands are spaced at less than a cm but en echelon vein arrays are spaced at 500 cm. These arrays indicate top-to-the southeast shear on southeast dipping brittle-ductile shear zones. Vein textures indicate cracking and sealing of thin veins in the matrix, but thicker veins in en echelon sets record initial cracking and sealing followed by periodic collapse of fracture porosity at a frequency that is lower than the frequency of crack-seal cycles. Silica depletion zones in the wall rock adjacent to veins indicate local transport of silica by diffusion. By combining the maximum time in which diffusion could dominate over advection with the time needed to precipitate the quartz associated with one crack-seal band, we show that a reasonable range of ΔP, or pressure difference between matrix and crack, can produce crack seal bands in less than 10 days. This time frame is less than the recurrence of earthquakes, and similar to the duration of some slow earthquakes in nature. Therefore, silica redistribution could play a role in modulating the frequency of plate boundary slip instabilities along convergent plate boundaries.

Magnetotelluric studies over the igneous arc of the Indo Burman range in the Sagaing province of Myanmar have delineated the high resistivity Indian plate subducting westwards beneath the Burmese block to depths of 30 km and beyond. The thick moderately resistive (20–100 Ω m) layer overlying the subducting Indian plate may be due to the low resistivity sediments. The entire region is covered with prominent sedimentary layer with a conductance varying between 20 and 3000 S showing a general increase from the east to west, suggesting that their thickness increases toward the west. The large unsystematic variations in the conductance are indicative of the widely varying depositional environments and also possible vertical block movements during the course of their deposition. A west dipping low resistivity zone to the east of Burmese block seems to demarcate its eastern limit, suggesting the possibility of a hitherto unknown deep seated fault, which is also supported by the several earthquake foci located over this zone. The nature of the crustal movements over this fault is not immediately apparent. Possibility exists that the Sagaing fault is an en echelon fault and the present feature observed here is a part of this en echelon fault. The possibility of channel flows of the weakened rocks in the deep crust observed in the vicinity of the eastern Himalayan syntaxis may also cause such low resistivity zones.

High-resolution, single-channel seismic and multibeam bathymetry data collected at the Amendolara Ridge, a key submarine area marking the junction between the Apennine collision belt and the Calabrian subduction forearc, reveal active deformation in a supposedly stable crustal sector. New data, integrated with existing multichannel seismic profiles calibrated with oil-exploratory wells, show that middle to late Pleistocene sediments are deformed in growth folds above blind oblique-reverse faults that bound a regional pop-up. Data analysis indicates that ~10 to 20 km long banks that top the ~80 km long, NW-SE trending ridge are structural culminations above en echelon fault segments. Numeric modeling of bathymetry and stratigraphic markers suggests that three 45° dipping upper crustal (2–10 km) fault segments underlie the ridge, with slip rates up to ~0.5 mm/yr. Segments may be capable with M ~ 6.1–6.3 earthquakes, although an unknown fraction of aseismic slip undoubtedly contributes to deformation. The fault array that bounds the southern flank of the ridge (Amendolara Fault System) parallels a belt of Mw

International audience; The 16 N segment of the East Pacific Rise is the most overinflated and shallowest of this fast-spreading ridge, in relation with an important magma flux due to the proximity of the Mathematician hot-spot. Here, we analyze the detailed morphology of the axial dome and of the Axial Summit Trough (AST), the lava morphology, and the geometry of fissures and faults, in regard to the attributes of the magma chamber beneath and of the nearby hotspot. The data used are 1 m resolution bathymetry combined with seafloor photos and videos. At the dome summit, the AST is highly segmented by 10 third-order and fourth-order discontinuities over a distance of 30 km. Often, two contiguous and synchronous ASTs coexist. Such a configuration implies a wide (1100 m minimum) zone of diking. The existence of contiguous ASTs, their mobility, their general en echelon arrangement accommodating the bow shape of the axial dome toward the hotspot, plus the existence of a second magma lens under the western half of the summit pla-teau, clearly reflect the influence of the hotspot on the organization of the spreading system. The different ASTs exhibit contrasted widths and depths. We suggest that narrow ASTs reflect an intense volcanic activity that produces eruptions covering the tectonic features and partially filling the ASTs. AST widening and deepening would indicate a decrease in volcanic activity but with continued dike intrusions at the origin of abundant sets of fissures and faults that are not masked by volcanic deposits.

The Gulf of Suez rift is dominated by NNW- to NW-striking “Clysmic” faults trending parallel to the rift. In addition there are NNE- and WNW-striking (oblique) faults that trend at an angle to the rift. The Durba–Araba fault (DAF) in southwestern Sinai represents one of several NNE-striking faults. It separates the Durba fault block on its NW from the Araba fault block on its SE. Detailed (1:20,000 scale) field mapping and structural studies of the DAF and the onshore area to the east of Belayim Bay (eastern margin of the central Gulf of Suez rift), indicate that the exposed part of the DAF extends for 7.5 km NNE from the mouth of Wadi Araba, at which point it bends and splays into three N- to NNW striking faults, forming a horse tail structure. The fault shows 4 km of pure sinistral strike-slip displacement. Northerly plunging fault propagation folds in the Phanerozoic rocks adjacent to the DAF accommodated the sinistral displacement. These folds are cut and displaced by the splay faults. Near its northern end, the middle splay fault affects the Pliocene El Qa’a Formation. At Gebel Qabeliat a group of en echelon left-stepping NNE- to N-striking faults overlaps the DAF generating a pull-apart (rhomb) graben, in which Pliocene and Quaternary sediments are downthrown against the Upper Miocene rocks. Kinematic indicators on most of these faults show major sinistral strike-slip movement. Palaeostress analysis of slip striae indicates sub-horizontal ENE to NNE extension, comparable to the present day stress regime. Cross-cutting relationships indicate that the NNE- to N-striking oblique faults are younger than the NW-striking Clysmic faults. These faults are probably presently active since they affect Pliocene and Quaternary sediments. It is proposed that these faults are related to the Aqaba-Levant transform that has been active since the Middle Miocene.

An important but poorly constrained issue for neoarchean orogenic lode-gold deposits of the southern Abitibi subprovince is whether they were reactivated, reworked or even enriched by younger hydrothermal fluids. The Young-Davidson mine is a lode-gold deposit that at least in part was structurally controlled. It experienced polyphase deformation and contains multiple generations of auriferous veins. Four stages of veining (V 1 –V 4 ) occurred after the emplacement of the host Neoarchean syenite. V 1 –V 3 veins formed during Neoarchean time and were responsible for the major phase of gold mineralization of the Young-Davidson deposit. Crosscutting V 1 –V 3 veins is a distinct group of V 4 planar to en echelon carbonate-quartz ± hematite ± epidote veins, which also cut both of the Neoarchean syenite and Paleoproterozoic Matachewan diabase dyke. Hydrothermal monazite extracted from the V 4 veins gives a 235 U- 207 Pb age of 1730 ± 5 Ma. This represents the first Paleoproterozoic age reported from Neoarchean gold deposits of the southern Abitibi subprovince. The hydrothermal activity was most likely related to the far-field 1750–1700 Ma Killarnean or Yavapai magmatism and metamorphism event that ultimately reactivated the pre-existing Neoarchean structures. This Paleoproterozoic activity provides a new perspective for understanding Neoarchean lode-gold deposits of the Abitibi.

The 4 April 2010 moment magnitude (M_w) 7.2 El Mayor–Cucapah earthquake revealed the existence of a previously unidentified fault system in Mexico that extends ∼120 km from the northern tip of the Gulf of California to the U.S.–Mexico border. The system strikes northwest and is composed of at least seven major faults linked by numerous smaller faults, making this one of the most complex surface ruptures ever documented along the Pacific–North America plate boundary. Rupture propagated bilaterally through three distinct kinematic and geomorphic domains. Southeast of the epicenter, a broad region of distributed fracturing, liquefaction, and discontinuous fault rupture was controlled by a buried, southwest-dipping, dextral-normal fault system that extends ∼53 km across the southern Colorado River delta. Northwest of the epicenter, the sense of vertical slip reverses as rupture propagated through multiple strands of an imbricate stack of east-dipping dextral-normal faults that extend ∼55 km through the Sierra Cucapah. However, some coseismic slip (10–30 cm) was partitioned onto the west-dipping Laguna Salada fault, which extends parallel to the main rupture and defines the western margin of the Sierra Cucapah. In the northernmost domain, rupture terminates on a series of several north-northeast–striking cross-faults with minor offset (

Within the southern Abitibi greenstone belt of the Superior Province, intrusion-related, in particular syenite-hosted gold deposits represent a significant type that is poorly understood. Whether the gold mineralization is genetically linked to the syenite intrusions (as in a magmatic model) or structurally associated with the development of subsequent shear zones remains very controversial. Our new structural data show that the multiply deformed Young-Davidson gold deposit and its surrounding Matachewan area occur along the western extension of the Cadillac – Larder Lake Deformation Zone (CLLDZ), a tectonically and economically important crustal-scale deformation zone in the southern Abitibi greenstone belt. Four generations (D1–D4) of deformation are recognized. The first part of the D1 deformation (D1a) records a NE-SW-oriented shortening and resulted in regional upright folding without penetrative foliation, whereas the subsequent D1b generates regional penetrative foliations and top-to-NE reverse faults. D2 occurs during a NW-SE-oriented shortening and produces asymmetric folds, oblique-slip thrusts and dextral strike-slip shear zones. D3 semi-brittle deformation refolds the D1 and D2 fabrics, whereas the latest D4 sinistral fault records a Paleoproterozoic brittle deformation. The Young-Davidson deposit is a lode-gold deposit that at least in part was structurally controlled. It is associated with the development of the CLLDZ and hosted in a syenite. Four main generations of veins are identified in the syenite. V1 veins are characterized by folded and boudinaged quartz–ankerite veins, V2 veins are represented by folded or en echelon quartz–pyrite veinlets, V3 veins are comprised of en echelon quartz–carbonate veins with sulfide minerals, and V4 veins consist of planar carbonate-quartz veins and minor hematite. Petrological studies reveal that the major phase of gold mineralization is associated with the V2 veins and partially with the V3 veins. Gold mineralization and emplacement of the associated veins appear to have occurred during regional D1b NE-SW-oriented shortening and top-to-NE shearing and the syenite acted as a mechanical trap due to competency contrast to the wall rock

We attribute changes in the morphology of relay ramp channels (increased slope and decreased width) to variations in displacement rate on ramp-adjacent normal faults. We map the faults and fluvial channels associated with four sites in different stages of fault interaction and linkage on the Volcanic Tableland, a Late Pleistocene ash-flow tuff in east-central California. Because these channels are inactive today, we estimate downstream changes in channel width and depth using HEC-RAS, a one-dimensional open channel flow model. Our results show that channel slope must be greater than about 0.05 before there are substantial decreases in width or substantial increases in depth. Displacement rate increases during interaction between en echelon segments results in the increases in channel slope and decreases in channel width. Moreover, our data show that these changes begin to occur during the very early stages of fault interaction, well before the fault geometry would indicate ongoing or imminent linkage.

The M-w 8.6 and 8.2 strike-slip earthquakes that struck the northeast Indian Ocean on 11 April 2012 resulted in coseismic deformation both at near and distant sites. The slip distribution, deduced using seismic-wave analysis for the orthogonal faults that ruptured during these earthquakes, is sufficient to predict the coseismic displacements at the Global Positioning System (GPS) sites, such as NTUS, PALK, and CUSV, but fall short at four continuous sites in the Andaman Islands region. Slip modeling, for times prior to the events, suggests that the lower portion of the thrust fault beneath the Andaman Islands has been slipping at least at the rate of 40 cm/yr, in response to the 2004 Sumatra-Andaman coseismic stress change. Modeling of GPS displacements suggests that the en echelon and orthogonal fault ruptures of the 2012 intraplate oceanic earthquakes could have possibly accelerated the ongoing slow slip, along the lower portion of the thrust fault beneath the islands with a month-long slip of 4-10 cm. The misfit to the coseismic GPS displacements along the Andaman Islands could be improved with a better source model, assuming that no local process contributed to this anomaly.

The Himalaya is the result of the on-going convergence and collision of India and Asia. The internal configuration and processes that govern the rise of the Himalayan Mountains and Tibetan Plateau are crucial to understand continental collision zones. However, knowledge of the prior configuration of the colliding plates is equally important, since inherited (pre-orogenic/basement) structures can undeniably influence the development of the orogenic architecture throughout the orogen's cycle of collision and eventual collapse. Three northeast-trending palaeotopographic ridges of faulted Precambrian Indian basement underlie the Ganga basin south of the Himalaya. Our paper illustrates a crustal-scale fault origin for these ridges and succeeds in determining how far north beneath the Himalayan system they extend and how they ultimately govern the location of upper crustal faults in southern Tibet. Spectrally filtered EGM2008 Bouguer gravity data and edges in its horizontal gradient at different source depths ('gravity worms') over northern Peninsular India, the Himalaya and southern Tibet reveal several continuous Himalayan cross-strike discontinuities interpreted to represent crustal faults. Gravity lineaments in Peninsular India coincide with edges of the Precambrian basement ridges and megakinks up to 100 km wide develop in foreland cover sequences between the interpreted basement faults. The interpreted basement faults project northward beneath the Himalayan system and southern Tibet. Our results suggest that several active Himalayan cross-strike faults, such as the ones related to many graben in southern Tibet, are rooted in the underplated Indian lower crust or step en echelon along interpreted basement faults. Our interpretation thus suggests that south Tibet graben are spatially related to deep-seated crustal-scale faults rooted in the underplated Indian crust. These major discontinuities partition the Himalayan range into distinct zones, and could ultimately contribute to lateral variability in tectonic evolution along the orogen's strike.

Large NE–SW oriented asymmetric inversion anticlines bounded on their southeastern sides by reverse faults affect the exposed Mesozoic and Cenozoic sedimentary rocks of the Maghara area (northern Sinai). Seismic data indicate an earlier Jurassic rifting phase and surface structures indicate Late Cretaceous-Early Tertiary inversion phase. The geometry of the early extensional fault system clearly affected the sense of slip of the inverted faults and the geometry of the inversion anticlines. Rift-parallel fault segments were reactivated by reverse slip whereas rift-oblique fault segments were reactivated as oblique-slip faults or lateral/oblique ramps. New syn-inversion faults include two short conjugate strike-slip sets dissecting the forelimbs of inversion anticlines and the inverted faults as well as a set of transverse normal faults dissecting the backlimbs. Small anticline–syncline fold pairs ornamenting the steep flanks of the inversion anticlines are located at the transfer zones between en echelon segments of the inverted faults.

GPS field and seismic data show that the southeastern margin of the Tibetan Plateau is tectonically and seismically active. This activity is due to the southeastward extrusion of the Chuandian fragment, a large crustal block rotating clockwise around the northeastern syntaxis of the Himalayas. The eastern boundary fault of this fragment is defined by the left-lateral Xianshuihe-Xiaojiang fault, which abruptly truncates the Sichuan basin of the Yangtze block. Our paper presents evidence indicating that the Sichuan basin experienced right-lateral shear along its margin, including the Longmen Shan fault belt, as shown by the presence of a large number of interference deformation features, including S-shaped and Z-shaped folds and faults, aligned in an en echelon pattern. This study hypothesizes that the Sichuan basin experienced counterclockwise rotation, dragged by the left-lateral movement along the Xianshuihe fault, and it is this rotation that was the underlying cause of the 12 May 2008 Wenchuan Ms 7.9 earthquake. During the rotation, the Sichuan basin decoupled along a subhorizontal decollement fault zone that developed along Triassic gypsum- and coal-bearing rocks, at a mean depth of ~5000 m, below which the Paleozoic rocks experienced much more intense deformation than the overlying Mesozoic rocks, suggesting that the lower part of the basin experienced a larger-scale rotation relative to the uppermost part of the basin. Based on thermal data from the western margin of the Sichuan basin and from along the Xianshuihe fault, the counterclockwise bending/rotation of the Sichuan basin initiated in late Cenozoic time (~13 Ma).

The beginning stages of melt segregation and the formation of leucosomes are rarely preserved in migmatites. Most arrays of leucosomes record a more advanced stage where flow dominates over segregation. However, the early stages in the formation of leucosomes and the segregation of melt are preserved in a partially melted meta-argillite from the metatexite zone (>800 °C) of the contact aureole around the Duluth Complex, Minnesota. The rock contains 2.4 modal% leucosome in a matrix consisting of 40.5% in situ neosome and 57.1% cordierite + plagioclase framework. The domainal microstructure in the matrix is a pre-anatectic feature resulting from the bulk composition. Terminal chlorite reactions produced a large volume of cordierite which, with plagioclase, formed a framework that enclosed patches of biotite + quartz + plagioclase ± K-feldspar. Upon melting, these fertile domains became patches of in situ neosome. Plagioclase in the neosome is less sodic than in the leucosome, hence segregation of melt occurred during crystallization, not melting. Segregation was delayed because the cordierite + plagioclase framework was strong enough to resist dilatation and compaction until after crystallization started. The leucosomes are small (i.e. they are microleucosomes) and display a systematic progression in morphology as length and aspect ratio increase from ~1 to 19 mm and from ~2.5 to >30 respectively. Small equant micropores form first, and in places these coalesce into small (~1 mm, aspect ratio ~2.5), isolated, blunt-ended, elliptical microleucosomes. In the next stage, micropores develop ahead of, and at ~45° to the left and right of the blunt tip of a microleucosome; one of these develops into an elliptical leucosome and an en echelon array of either a left- or right-stepping elliptical microleucosome forms. Each elliptical microleucosome in the en echelon arrays is separated by a bridge of matrix. Next, microleucosomes of greater length (>4 mm) and aspect ratio (>5) form when the bridges of cordierite + plagioclase matrix rupture and the elliptical microleucosomes link together to form a zigzag-shaped microleucosome. Finally, still longer microleucosomes with greater aspect ratios (~30) are formed by the joining of zigzag arrays. Such a progression is characteristic of the way ductile fractures grow. The segregation of melt was driven by the pressure gradient between the dilatant fracture and an adjacent in situ neosome, which drew melt to the growing fracture, thereby creating a microleucosome. The microleucosomes are filled arrays of ductile fractures. Melt was contiguous only between microleucosomes and adjacent patches of in situ neosome. The length-scale of segregation was ~5 mm, the size of a typical patch of in situ neosome, and restricted by the surrounding impermeable cordierite + plagioclase framework. The melt in the microleucosome was the most fractionated and the last to crystallize. All microleucosomes contain entrained minerals as a consequence of their mechanism of growth. Rupture of the bridges resulted in the entrainment of pre-anatectic phases. However, microleucosomes that cross patches of in situ neosome are also contaminated with peritectic phases that were transported with the melt.

Based on multiple types of data, the topographical features of the Okinawa Trough (OT) have been characterized and a computation method has been proposed to determine the break point of continental shelf (BOS), foot point of the continental slope (FOS), the central axial point, and the maximum depth point. A total of 48 topographical profiles that crosscut the continental slope have been used to determine the trends of the BOS and FOS (the BOS and FOS lines) in the East China Sea (ECS). The trend of central axial points in the OT has been similarly determined by analyzing 39 topographical profiles across the axis of the trough. The BOS line forms the boundary between the continental shelf and slope. In the ECS, the BOS line roughly follows the 200 m isobath, continuously in the northern and middle parts of the OT, but jumping about somewhat in the south. The FOS line is the boundary between the continental slope and the bottom of the trough. The depth of the FOS increases gradually from north to south in the OT. Intense incisions by canyons into the slope in the southern part of the trough have led to the complex distribution of FOS. Topographical profiles crosscutting the northern, middle, and southern parts of the OT exhibit features that include: a single W-shape, a composite W-shape, and a U-shape, respectively, which suggests that in the middle and northern parts of the trough the central axial points are always located on seamount peaks or ridges associated with linear seamounts, whereas in the south they are found in the center of en echelon depressions. The line formed by the central axial points is the east-west dividing line of the OT, which indicates that the trough is a natural gap that prevents the extension of ECS continental shelf to the east. The distributions of the BOS and FOS lines are influenced by fluctuation of sea levels and submarine canyons, whereas the distribution of axis lines is controlled by tectonics and deposition.

The Gebel Yelleg area includes a number of folds belonging to the northern Sinai Syrian Arc structures. Detailed surface structural mapping and subsurface (seismic and borehole) data show that the Gebel Yelleg structures are related to Late Cretaceous-Early Tertiary inversion of a Jurassic asymmetric (or half) graben formed during the opening of Neotethys. The inversion structures include a large (45-km long) asymmetric fold (Yelleg Anticline) with a steep flank overlying the southeastern (main) bounding fault of the inverted half graben as well as some right-stepped en echelon folds overlying the northwestern bounding fault of the half graben. The large inversion anticline is dissected by a large number of long, nearly orthogonal normal faults whereas the en echelon folds are dissected by transverse normal faults and two sets of oblique-slip faults. Inversion of the northern Sinai extensional basins is related to Africa-Eurasia convergence and was probably transpressional with a small component of dextral slip. This study shows that the magnitude of inversion in the northern Sinai fold belt decreases toward the southern boundary of the Jurassic extensional province.

Investigations of geometry and kinematics of foreland fold-and-thrust belts provide key information for understanding how convergence is accommodated in deformed forelands of orogenic belts. Here, we present the structural styles, deformation ages and shortening rates of three en echelon anticlines located at the west end of the Baicheng-Kuqa foreland fold-and-thrust belt. The results indicate that the three anticlines developed above the Eocene evaporites of the Kumugeliemu Group which constitute the decollement level in this typical thin-skinned tectonics. The initial growth of the East Awate and North Kalayuergun anticlines, as indicated by the syn-tectonic growth strata accumulations, occurred at ~5.3 Ma with shortening rates of ~0.70–0.77 mm/yr and ~0.40–0.43 mm/yr, respectively. Whereas, the initial folding time of the Middle Kalayuergun anticline is ~2.6–1.7 Ma, resulting in a shortening rate of ~0.35–0.65 mm/yr. The shortening rates are lower when compared with foreland deformation in the middle and eastern parts of the Baicheng-Kuqa fold-and-thrust belt. Such differences are mostly related to the strain partitioning caused by the NW-SE dextral strike-slip Kalayuergun fault as well as the influence of a dextral wrenching component in the west end of the Baicheng-Kuqa fold-and-thrust belt. Our study suggests that episodic tectonic deformation in the southern foreland of Tian Shan has been a response to the ongoing India-Asia convergence since the latest Miocene, and the spatial variability of crustal shortening rates has depended on regional tectonic differences.

The Himalayan foreland in N Pakistan, dissected by Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT) contains spectacular salients and syntaxes. The lateral (N-S) boundaries between these salients and syntaxes around Kalabagh city and east-southeast of Islamabad were believed to host deep-seated lateral ramps with strike slip movements. However, seismic data in these two sectors suggest that there are N-S trending folds and locally east- or west-vergent thrusts that affect the Paleozoic-Paleogene cover of the Indian shield, as well as the Miocene-Pliocene molasse sediments. The proposed lateral ramps cannot be followed on the seismic and on maps either; instead, both maps and seismic data suggest folding, often on a regional scale of harder Paleo-Mesozoic-Paleogene and softer Oligo-Miocene-Pilo-Pleistocene cover. The NE corner of Surghar range is proposed to be formed of relaying thrust sheets with emergent heads composed of Paleozoic-Paleogene and its slightly detached Miocene molasse. These relaying imbricates are taken in a southward flexure generated by a major right lateral shear of a wide zone, where transpressive Riedel shears, en echelon anticlines and southwards flexed earlier thrust faults are the main elements (but a single, through-going Kalabagh fault is missing). The generation of mapped N-S trending folds and east-vergent thrusts preceded the formation of the wide shear zone and southwards flexing.Hazara syntaxis is interpreted as a major antiform that re-folded MBT and Panjal thrust around Oligo-Miocene molasse, itself forming an antiform (BOSSART ET AL. 1988). In our model we propose that the west-vergent Balakot thrust and deeper blind thrusts are in the core of this antiform. In the southern continuation we propose that folds in Miocene molasse continue from eastern Potwar region to western Kashmir and there appears no major break. These structures are also re-folded in a major antiform with N-S axial trend. Map analysis also suggests that N-S trending folds bending earlier main thrusts are occurring in a wide area south of the Indus-Tsangpo suture.Several independent geological and geophysical observations including mapping, seismic analysis, earlier measurements of strain axes and of paleomagnetic declinations suggest that the salients and syntaxes may have been much more linear in the past (although a total linearity is not realistic). It is proposed that the present-day undulating pattern may have been generated by N-S trending folds due to general (and episodic) E-W shortening. If the main fault zones were more linear, the relay pattern along their segments suggests a left lateral shear component along MBT and a mixed, locally left, locally right lateral component along MFT. Earlier (ZEITLER 1985) and now provided low temperature thermochronological ages strongly suggest a rather general episode of E-W shortening between 4-5 Ma for the whole northern Indian margin. However, there should have been original transversal dome formation as early as Oligocene (DIPIETRO ET AL. 2008). It is also clear that longer N-S shortening and shorter E-W shortening episodes should alternate eventually in a very short time frame, since earthquake focal mechanisms (LISA AND KHWAJA 2004, BURG ET AL. 2005) suggest the coexistence of E-W compression and NW-SE compression in Potwar.There are several potential explanations for generating E-W shortening and related structures in a general N-S shortening regime. Possibilities range from fault terminations of thrust faults at high angles in a particular zone (TREOLAR ET AL. 1992) to en echelon folding along a major right lateral E-W fault zone. However, we speculate that E-W shortening could be much more general, suggesting a mechanism that affects the whole of Indian plate. Possibly the best explanation is given by analogue models (REPLUMAZ ET AL. 2012) proposing major, slightly convergent confining boundaries. If applied to the northwards advance of India, the northwards converging boundaries generate secondary E-W shortening and east-or west-vergent orogens parallel to these boundaries.

The Shillong plateau in northeast India constitutes an actively deforming anticlinal basement uplift in the foreland of the Himalayas in the north and the Indo-Burman ranges in the east. The study aims to document zones of active crustal deformation in the Shillong plateau through the interpretation of the geometry and the quantitative analysis of stream profiles derived from 30-m SRTM DEM. Longitudinal profiles of the streams draining the plateau exhibit conspicuous convex upward reaches, mainly to the upstream of faults and in areas of deep river incision. Analysis of river profiles using Hack’s stream-gradient index (SL-index) reveals perturbations in profiles and steep channel-gradients in the middle reaches of the streams. Spatial distribution of the SL-index brings out extensive zones of anomalously high stream-gradients along the monoclinal flexure at the southern margin of the plateau adjacent to the Dauki fault and along the northern margin, where multiple en echelon faults define step-like topography. In the western part of the plateau, spatial association of zones of high stream-gradients with well-defined fault-scarps is suggestive of active crustal deformation by differential vertical movement along faults. The observed spatial distribution of anomalously high stream-gradients is uncorrelated with the lithological variations and hence, perturbations in river profiles and abrupt changes in stream-gradients are suggestive of differential tectonic uplift of the plateau. The study suggests that the rate of active tectonic deformation in the plateau decreases from the east to the west.

The North-western Bonaparte Basin offers a very good opportunity to understand the nature of oblique extension system, where Neogene flexure-induced extension was superimposed obliquely to the Mesozoic rift-related structures. The Mesozoic trends strongly control the distribution and style of the younger Neogene structures, both at regional and local scale. The younger Neogene activity produced a new set of NE trending, right-stepping en echelon faults and reactivated the older faults. In addition, episodes of stratigraphic growth provide critical evidence regarding the timing of fault activity. Results demonstrate that, in the study area, main fault activity occurred in several pulses during the latest Miocene to Late Pleistocene. These episodes of fault activity correspond to recently constrained regional tectonic events i.e., the initial collision of the Australian Plate with the Banda Arc, the episodes of uplift of the Timor Island and the timing of lithospheric flexure.

International audience; The Quito Fault System (QFS) extends over 60km along the Interandean Depression in northern Ecuador. Multidisciplinary studies support an interpretation in which two major contemporaneous fault systems affect Quaternary volcanoclastic deposits. Hanging paleovalleys and disruption of drainage networks attest to ongoing crustal deformation and uplift in this region, further confirmed by 15 years of GPS measurements and seismicity. The resulting new kinematic model emphasizes the role of the N-S segmented, en echelon eastward migrating Quito Fault System (QFS). Northeast of this major tectonic feature, the strike-slip Guayllabamba Fault System (GFS) aids the eastward transfer of the regional strain toward Colombia. These two tectonic fault systems are active, and the local focal mechanisms are consistent with the direction of relative GPS velocities and the regional stress tensor. Among active features, inherited N-S direction sutures appear to play a role in confining the active deformation in the Interandean Depression. The most frontal of the Quito faults formed at the tip of a blind thrust, dipping 40 degrees W, is most probably connected at depth to inactive suture to the west. A new GPS data set indicates active shortening rates for Quito blind thrust of up to 4mm/yr, which decreases northward along the fold system as it connects to the strike-slip Guayllabamba Fault System. The proximity of these structures to the densely populated Quito region highlights the need for additional tectonic studies in these regions of Ecuador to generate further hazard assessments.

Integrated structural, anisotropy of magnetic susceptibility (AMS), and paleomagnetic analyses of sedimentary cover rocks along variably oriented major faults and en echelon fold systems in the southern Bighorn Arch, Wyoming, were undertaken to test kinematic and mechanical models of Laramide thick-skin deformation. The Laramide foreland is characterized by an anastomosing network of basement-cored arches and associated cover folds that trend overall NW-SE, but in detail are curved, range from N-S to E-W trending, and form both right- and left-stepping en echelon systems. Development of variably trending Laramide arches has been variously attributed to temporal changes in stress directions, wrench faulting, and localization of deformation related to basement heterogeneities during regional SW-NE shortening. Within the southern Bighorn Arch, widespread but limited layer-parallel shortening (LPS) was accommodated mostly by minor faults with conjugate wedge and strike-slip geometries early in the deformation history. LPS directions vary from perpendicular to acute with local fold structural trends, consistent with a single shortening episode. Although internal strain is limited, weak AMS lineations defined by kinked and rotated phyllosilicates are widely developed and consistently perpendicular to LPS directions. Structurally restored paleomagnetic declinations record only limited, non-systematic vertical-axis rotations, indicating that wrenching was not an important component of the deformation field during development of the southern Bighorn Arch and that curvature of the arch was a primary feature. Palinspastically restored LPS directions are on average WSW-ENE, but display local deflections related to heterogeneities of underlying basement blocks and proximity to major faults, some of which were localized along Precambrian shear zones and igneous dikes. Crustal shortening patterns across the Laramide foreland are interpreted to reflect deformation partitioning in response to a single far-field shortening direction partly related to flat-slab subduction along with effects of pre-existing basement weaknesses and strain softening during progressive faulting.

Granitic rock mass of the upper Aar valley (Grimsel area, Switzerland) contains distinct generations of exfoliation joints, which formed during different stages of the Pleistocene, subparallel to distinct glacial valley palaeotopography. The bulk of exfoliation joints shows prominent, common fractographic features: (1) radial plumose structures with distinct plume axes; (2) arrest marks superimposed by plumose striations; and (3) gradually-developing en echelon fringe cracks. Multiple arrest marks reveal that exfoliation joints formed incrementally and, together with the absence of hackle fringes, suggest stable, i.e., subcritical fracturing conditions. Smooth transitions from plumose structures on the parent plane to en echelon fringe cracks, combined with non-systematic stepping senses of fringe cracks, suggest local (vs. temporal) stress field variations. Assuming that plume axes formed parallel to the maximum principal compressive stress (σ1) enables us to infer near-surface palaeostress orientations and compare them with classical borehole-based in-situ stress data. The majority of plume axes suggest (1) persistently subhorizontal to slightly inclined σ1 orientations at trough valley slopes and (2) near-surface variability of σ1 orientations originating from topographic perturbation caused by glacial valley erosion superimposed on the regional stress field. Our investigations of fracture surface morphologies yield unique insights into exfoliation fracture formation, such as directional trends of fracture propagation and associated palaeostress orientations within Alpine valley slopes.

[1] We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ∼40 m horizontally and ∼120 m vertically. Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American-Pacific plate boundary and en echelon, conjugate features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three-dimensional analysis reveals individual and intersecting fault planes that are limited in their along-strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner.

We use GPS, bathymetric/structural, and seismic data to define the pattern of present deformation along the northern half of the Azores plateau, where the Nubia–Eurasia plate boundary terminates at the axis of the Mid-Atlantic Ridge (MAR). New and existing campaign GPS velocities from the Azores islands reveal extension oblique to a series of en echelon volcanic ridges occupied by Terceira, S. Jorge, Pico, and Faial islands. In a frame of reference defined by 69 continuous GPS stations on the Eurasia plate, Terceira Island moves 2 ± 1 mm / yr away from Eurasia, consistent with the islandʼs location within the Terceira Rift and plate boundary structure. The volcanic ridges south of the Terceira Rift move toward WSW at progressively faster rates, reaching a maximum of 3.5 ± 0.5 mm / yr ( 2 - σ ) for the Pico/Faial volcanic ridge. The hypothesis that the Terceira Rift accommodates all Nubia–Eurasia plate motion is rejected at high confidence level based on the motions of sites on S. Jorge Island just west of Terceira Rift. All of the islands move relative to the Nubia plate, with Pico Island exhibiting the slowest motion, only 1 ± 0.5 mm / yr ( 2 - σ ). Detailed bathymetry from the interior of the hypothesized Azores microplate reveals faults that crosscut young MAR seafloor fabric. These observations and the GPS evidence for distributed deformation described above argue against the existence of a rigid or semi-rigid Azores microplate, and instead suggest that Nubia–Eurasia plate motion is accommodated by extension across a ∼140-km-wide zone east of the MAR axis, most likely bounded to the north by the northern shoulder of the Terceira Rift. The MAR spreading rate along the western end of the Azores deformation zone (∼38.5°N–39.5°N) is intermediate between the Eurasia–North America rate measured at 39.5°N and the Nubia–North America rate measured at 38.5°N, consistent with the joint conclusions that the Nubia–Eurasia boundary is broad where it intersects the MAR, and the Azores Triple Junction is diffuse rather than discrete.

The Tan-Lu fault zone (TLFZ) traverses the Liaohe western depression (LHWD), affords an exceptional opportunity to reveal the structural deformation and evolution of a major strike-slip fault of the LHWD using three dimensional seismic data and well data. In this paper, based on structural interpretations of the 3-D seismic data of the LHWD, combined with depth slice and seismic coherency, a variety of structural features in relation to right-lateral strike-slip fault (the western branch of the Tan-Lu fault) have been revealed presence in the depression, such as thrust faults (Xinlongtai, Taian-Dawa, and Chenjia faults), structural wedges, positive flower structures, and en echelon normal faults. Fault cutoffs, growth strata and the Neogene unconformity developed in the LHWD verify that the activity of right-lateral strike-slip from the late Eocene to Neogene (ca. 43–23 Ma). The study indicates that the right-lateral strike-slip played an important role in controlling the structural deformation and evolution of the LHWD in the early Cenozoic. Moreover, the front structural wedge generated the gross morphology of the Xinlongtai anticline and developed the Lengdong faulted anticline during the late Eocene, and the back structural wedge refolded the Lengdong faulted anticline zone in the late Eocene to the early Oligocene. Wrench-related structures (the Chenjia thrust fault and the en echelon normal faults) were developed during the late Oligocene. Uniform subsidence in the Neogene to Quaternary. Furthermore, the driving force of the right-lateral strike-slip deformation was originated from N–S extension stress related to the opening of the Japan Sea and NE–SW compression, as the far-field effect of India–Eurasia convergence.

We conducted seismic multiattribute analysis by combining seismic data with wireline logs to determine hydrocarbon sweet spots and predict resistivity distribution (using the deep induction log) within the Austin Chalk and Eagle Ford Shale in South Texas. Our investigations found that hydrocarbon sweet spots are characterized by high resistivity, high total organic carbon (TOC), high acoustic impedance (i.e., high brittleness), and low bulk volume water (BVW), suggesting that a combination of these log properties is required to identify sweet spots. Although the lower Austin Chalk and upper and lower Eagle Ford Shale intervals constitute hydrocarbon-sweet-spot zones, resistivity values and TOC concentrations are not evenly distributed; thus, the rock intervals are not productive everywhere. Most productive zones within the lower Austin Chalk are associated with Eagle Ford Shale vertical-subvertical en echelon faults, suggesting hydrocarbon migration from the Eagle Ford Shale. Although the quality factor (Q) was not one of the primary attributes for predicting resistivity, it nevertheless can serve as a good reconnaissance tool for predicting resistivity, brittleness, and BVW-saturated zones. In addition, local hydrocarbon accumulations within the Austin Chalk may be related to Austin TOC-rich zones or to migration from the Eagle Ford Shale through fractures. Some wells have high water production because the water-bearing middle Austin Chalk on the downthrown side of Eagle Ford Shale regional faults constitutes a large section of the horizontal well, as evidenced by the Q attribute. Furthermore, the lower Austin Chalk and upper Eagle Ford Shale together appear to constitute a continuous (unconventional) hydrocarbon play.

The Anninghe, Zemuhe, Xiaojiang and Daliangshan faults bound the southeastern margin of the Tibetan Plateau, which has almost been entirely ruptured by strong earthquakes during the past 500 years. The geometry and deformation features of the most recent co-seismic surface ruptures show not only the surface morphology of the source seismogenic fault, but also the structural characteristics of the upper crust, as well as the pre-existing tectonic environment. Hence, the most recent co-seismic surface ruptures along the Xiaojiang Fault zone reveal the surface deformation of the southeastern Tibetan Plateau. Our investigation reveal that the 1833 Songming rupture zone is about 150 km, with maximum co-seismic offset of 8.4 m, and the re-evaluated moment magnitude is about M 7.5–7.6 which is lower than previously estimated M 8.0. The 1500 Yiliang rupture zone is about 80 km, with maximum co-seismic offset of 8.0 m, and the re-evaluated moment magnitude of M 7.2–7.5, which is higher than previously demonstrated M 7.0. The spatial distribution of the surface rupture zones along Xiaojiang Fault shows an arcuate geometry. Our findings also reveal that strong earthquakes rupture not only the two major strands but also the en echelon faults between them. The arcuate geometry of the fault zone and the development of these en echelon faults are consistent with the clockwise rotation of the southeastern Tibetan Plateau.

The Yinggehai Basin, lying along the trace of the Red River fault zone in the South China Sea, has been related to the movements of the Red River fault zone and the rotation of the Indochina block. However, the tectonic origin of the Yinggehai Basin remains unclear. This paper explores the initiation of the Yinggehai Basin using a visco-elasto-plastic model. This model concentrates on two main aspects: lateral viscosity variations (mainly controlled by temperature) in the lithosphere and internal friction angles of the pre-existing fault zone. Modeling results show that: (1) for a layered viscosity, en echelon faults would likely form when there is no pre-existing strike–slip fault; whereas, the basin would be narrow and deep, if any, when there is a pre-existing fault; (2) for moderate lateral viscosity variations, a large basin forms, even without a pre-existing fault zone; and (3) for strong lateral viscosity variations, a major rift could form over geologic time. Our results indicate that the initiation of the Yinggehai Basin requires moderate lateral viscosity variations (i.e., a pre-existing gentle upwelling of the Mohorovicic discontinuity) but no pre-existing fault. In addition, the initial extension predicted is NE–SW and is generated by the rotation of the Indochina block. This differs from the NW–SE extension that resulted from the movements of the Red River fault zone. This indicates that the left-lateral displacements of the Red River fault zone and the spreading of the South China Sea only influence the basin evolution after its initiation.

Detecting earthquake precursors is a difficult task in earthquake prediction at home and aboard. Carrying out rock deformation experiments in the laboratory and observing the evolution of the characteristics and rules of related physical parameters are fundamental to exploring of earthquake precursors. In this study, a sample of a compressive en echelon fault set was used to perform deformation experiments. An infrared thermal image system recorded temperature variations of the rock sample during the deformation stage. The deformation process with precursory significance is divided into strongly-off-linearity stage, meta- instability stage and instability stage based on the stress-time curve. The purpose of this work is to study the spatial and temporal variations of the thermal field in each stage especially the meta-instability stage and summarize the possible precursory phenomena. The experimental results show that the temperature in the jog area increases because of compressive stress state during the strongly-off-linearity stage. The temperature inside the fault decreases due to the crack in the jog area and the high temperature points on the fault spread and connect due to the converting of fault dislocation from local to overall during the stage of meta-instability. And the synergy of temperature increases on the fault and the synergy of temperature decreases between the faults (including the jog area), which are two important signals before the instability. The temperature of the whole sample decreases because of stress release except for increasing on the faults caused by friction during the instability stage. In short, there are evident characteristics of the thermal field in the stage of meta-instability, which can help identify the meta-instability state. The temperature varies in different deformation stages and different tectonic positions, which means the stage of the deformation and the tectonic position of anomalies should be taken into consideration when we attempt to find thermal anomalies related to tectonic activity.

Referring to the previous shearing model tests on intermittence jointed rock mass, DDARF method was adopted to conduct the corresponding numerical simulation. It could be concluded from the cracking failure phenomena that the results of the numerical simulation and the tests were in good agreement. Then the intermittence joints were arranged as en echelon and different cracking failure phenomena, peak shear strengths and strain-stress relationships were also obtained.

[1] At Santorini, active normal faulting controls the emission of volcanic products. Such geometry has implication on seismic activity around the plumbing system during unrest. Static Coulomb stress changes induced by the 2011–2012 inflation within a preexisting NW-SE extensional regional stress field, compatible with fault geometry, increased by more than 0.5 MPa in an ellipsoid-shaped zone beneath the Minoan caldera where almost all earthquakes (96%) have occurred since beginning of unrest. Magmatic processes perturb the regional stress in the caldera where strike-slip rather than normal faulting along NE-SW striking planes are expected. The inflation may have also promoted more distant moderate earthquakes on neighboring faults as the M > 5 January 2012, south of Christiania. Santorini belongs to a set of en echelon NE-SW striking rifts (Milos, Nysiros) oblique to the Aegean arc that may have initiated in the Quaternary due to propagation of the North Anatolian fault into the Southern Aegean Sea.

Late Paleoproterozoic dikes of the Maimakan Complex were studied in the Ulkan-Uchur district at the eastern margin of the Aldan-Stanovoi Shield. The dikes are parallel or arranged en echelon in the Uchur-Uyan, South Uchur, and Ukikan fields of dike swarms. The spatial distribution of the dike swarms pertaining to the Maimakan Complex in the Ulkan Trough and its framework shows that the area of their intersection is located in the center of the Ulkan granitoid batholith. The basic dikes, which are distinguished by elevated contents of alkali metals, Fe, Ti, and P in combination with a low Mg content, are defined as moderately alkaline rocks transitional from tholeiitic to alkaline series similar in composition to within-plate basalts and E-MORB. The REE pattern is comparable to that of tholeiitic and subalkaline series in extensional settings. Along with the geological data, this indicates that the complex was formed under conditions of intracontinental extension. As follows from geological relationships, the age of dikes is estimated as 1670–1715 Ma.

In terms of neotectonics, the Timan Range and Kanin Peninsula represent a spacious mountainous structure 1150 km long and 80–160 km wide extend� ing in the northwesterly direction from Mount Poly� udov Kamen to Cape Kanin Nos in the Kanin Penin� sula. It consists of isolated en echelon arranged horst� like uplifts with Upper Precambrian rocks cropping out in their arch parts. In the southwest the Timan Range borders the Pechora Plate that surrounds the Karelian part of the East European Platform in the northeast. The boundary between the Pechora Plate and Mezen megablock of the East European Platform

Hough Transform analysis is used as an objective means to constrain volcano distribution in the central Sunda Arc, Indonesia. Most volcanoes in the arc define four en echelon, linear segments, each of 500–700 km length. Javan volcanoes that do not lie on these segments either (i) formed at an early stage in the history of the arc and erupted products that are petrologically and geochemically distinct from typical arc magma, or (ii) lie along other mapped structures. The en echelon distribution of volcanoes in the central Sunda Arc is best explained as originating from two possible sources. First, interaction with the subducting Indo-Australian Plate may induce stress in the arc lithosphere generating pathways for magma to exploit. Second, downward flexure of the arc lithosphere, as a result of mantle flow or loading by the arc, would also establish arc-normal tension towards the base of the lithosphere, where magma is supplied to volcanic systems. To the west and east of the central Sunda Arc deviations from the distribution of long, en echelon, linear segments can be understood as responses to specific stress fields in the arc lithosphere of Sumatra and eastern Nusa Tenggara, respectively. Control of volcano distribution by arc lithosphere explains why there are large variations in the depth from volcanoes to the zone of slab seismicity in the central Sunda Arc, where there is little variation in slab geometry or the rate of plate convergence.

[1] A vigorous swarm of over 1000 small, shallow earthquakes occurred 20–22 September 2009 beneath Mount Rainier, Washington, including the largest number of events ever recorded in a single day at Rainier since seismic stations were installed on the edifice in 1989. Many events were only clearly recorded on one or two stations on the edifice, or they overlapped in time with other events, and thus only ~200 were locatable by manual phase picking. To partially overcome this limitation, we applied waveform-based event detection integrated with precise double-difference relative relocation. With this procedure, detection and location goals are accomplished in tandem, using cross-correlation with continuous seismic data and waveform templates constructed from cataloged events. As a result, we obtained precise locations for 726 events, an improvement of almost a factor of 4. These event locations define a ~850 m long nearly vertical structure striking NNE, with episodic migration outward from the initial hypocenters. The activity front propagates in a manner consistent with a diffusional process. Double-couple-constrained focal mechanisms suggest dominantly near-vertical strike-slip motion on either NNW or ENE striking faults, more than 30° different than the strike of the event locations. This suggests the possibility of en echelon faulting, perhaps with a component of fault opening in a fracture-mesh-type geometry. We hypothesize that the swarm was initiated by a sudden release of high-pressure fluid into preexisting fractures, with subsequent activity triggered by diffusing fluid pressure in combination with stress transfer from the preceding events.

We use interferometric synthetic aperture radar (InSAR), body wave seismology, satellite imagery, and field observations to constrain the fault parameters of the Mw 7.1 2011 Van (Eastern Turkey) reverse-slip earthquake, in the Turkish-Iranian plateau. Distributed slip models from elastic dislocation modeling of the InSAR surface displacements from ENVISAT and COSMO-SkyMed interferograms indicate up to 9 m of reverse and oblique slip on a pair of en echelon NW 40°-54° dipping fault planes which have surface extensions projecting to just 10 km north of the city of Van. The slip remained buried and is relatively deep, with a centroid depth of 14 km, and the rupture reaching only within 8-9 km of the surface, consistent with the lack of significant ground rupture. The up-dip extension of this modeled WSW striking fault plane coincides with field observations of weak ground deformation seen on the western of the two fault segments and has a dip consistent with that seen at the surface in fault gouge exposed in Quaternary sediments. No significant coseismic slip is found in the upper 8 km of the crust above the main slip patches, except for a small region on the eastern segment potentially resulting from the Mw 5.9 aftershock on the same day. We perform extensive resolution tests on the data to confirm the robustness of the observed slip deficit in the shallow crust. We resolve a steep gradient in displacement at the point where the planes of the two fault segments ends are inferred to abut at depth, possibly exerting some structural control on rupture extent. ©2013. American Geophysical Union. All Rights Reserved.

Multi-channel seismic profiles and swath bathymetric data were used to investigate the tectonic evolution of the South Korea Plateau (SKP) associated with the opening of the East Sea (Japan Sea). The SKP is a deformed fragment of continental crust with numerous horsts and sediment-filled grabens. Three sedimentary units in the plateau were identified, which consist of the lower sequence (Unit I) interpreted as syn-rifting deposition during the early to middle Miocene, and the middle and upper sequences (Units II and III) considered as post-rifting deposition since the late Miocene. The fault system in the SKP includes the South Korea Plateau Fault (SKPF) trending NNW-SSE and smaller en echelon normal faults oriented NE-SW. We interpreted the information to postulate that the formation of the SKPF is the result of divergent right-lateral strike-slip movement in the SKP. This study suggests that the dextral movement of the SKP was induced by WSW-ward propagation of the spreading center located in the Japan Basin from the early to middle Miocene times.

The deformation in the central part of Al Jabal Al Akhdar, NE Libya, is dominated by E-W right-lateral strike-slip fault zones that form a conjugate system with the N-S left-lateral strike-slip faulting. The dextral wrench-dominated transpression is responsible for the formation of strike-slip duplexes, en echelon folds, and thrusts that deform the Cretaceous-Eocene sedimentary sequences. The strike-slip duplex is formed by the progressive linkage of horsetail-like structures at the western tip of the Al Bayda strike-slip fault that joined splays coming from other dextral strike-slip faults. The master linear fault branches into second-order dextral or sinistral faults that regroup into a linear single fault. Faults started from arrays of en echelon extensional/extensional-shear fractures that then coalesced into throughgoing strike-slip faults. Shortening was accompanied by significant N-S-striking left-lateral strike-slip displacements, with the development of NE- to ESE- and SW-plunging major f...

Identifying individual subsurface faults in a larger fault system is important to characterize and understand the relationship between microseismicity and subsurface processes. This information can potentially help drive reservoir management and mitigate the risks of natural or induced seismicity. We have evaluated a method of statistically clustering power spectra from microseismic events associated with an enhanced oil recovery operation in southeast Utah. Specifically, we were able to provide a clear distinction within a set of events originally designated in the time domain as a single cluster and to identify evidence of en echelon faulting. Subtle time-domain differences between events were accentuated in the frequency domain. Power spectra based on the Fourier transform of the time-domain autocorrelation function were used, as this formulation results in statistically independent intensities and is supported by a full body of statistical theory upon which decision frameworks can be developed.

International audience; The ferocity of volcanic eruptions – their penchant for either effusive or explosive behaviour – is to a large extent a matter of the ease with which volatiles are able to escape the volcanic system. Of particular importance are the mechanisms by which permeable networks within magma are fabricated and how they permit gas escape, thereby diffusing possibly calamitous explosions. Here, we present a series of experiments that confirms sample-scale fracture propagation and permeability development during shearing viscous flow of initially impermeable, bubble-bearing (2×10−4 s−1). At moderate shear strain rates (2×10−4 s−13) via en échelon Mode I fractures produced by repeated fracture events. At high shear strain rates (γ˙>4.5×10−4 s−1), permeability develops shortly after the onset of inelastic deformation and is, again, established through a series of en échelon Mode I fractures. Critically, strain is not immediately localized on Mode I fractures, making them long-lived and efficient outgassing channels that are ideally oriented for directing volatiles from the central conduit upward and outward toward the conduit rim. Indeed, Mode I fracture arrays may prove necessary for dissipating gas overpressures in the central regions of the magma column, which are considered difficult to outgas. These experiments highlight mechanisms that are likely active along conduit margins and constrain previously postulated processes under truly applicable conditions.