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The quantitative morphology of bedrock fault surfaces combined with aerial surveys and field identification is a useful approach to identify paleoearthquakes, obtain coseismic slips, and evaluate the seismogenic capacity of active faults in bedrock areas where traditional trenching methods are not applicable. Here, we report a case study of the Jiaocheng Fault (JCF) in the Shanxi Rift, China. Although several studies have been conducted on the JCF, its coseismic slip history and seismogenic capacity are still unclear. To address these problems, we investigated two bedrock fault surfaces, Sixicun (SXC) and Shanglanzhen (SLZ), on the JCF’s northern segment using quantitative morphological analysis together with aerial and field surveys. Quantitative fractal analysis based on the isotropic empirical variogram and moving window shows that both bedrock fault surfaces have the characteristics of vertical segmentation, which is likely due to periodic earthquakes, the coseismic slip of which can be determined by the height of the segments. Three seismic events at SXC, with a coseismic vertical slip of 1.74, 1.65, and 1.99 m, and three seismic events at SLZ, with a coseismic vertical slip of 1.32, 2.35, and 1.88 m, are identified. Compared with the previous studies, these three seismic events may occur in the Holocene, but it requires absolute dating ages to support, which is also the focus of our future work. Considering the seismologic capability (M>7.5) and the relationship between the recurrence interval of ~2.6 kyr and elapsed time of more than 3 kyr, the seismic hazard of the northern and middle segments of the JCF requires immediate attention.

International audience

A historically documented M8.0 earthquake occurred in Tianshui, Gansu, China, in 1654. Its epicenter was located near the Lixian-Luojiapu fault in the triangular area at the conjunction of the Tibetan Plateau, North China block and South China block. Due to the lack of geologic and geomorphologic evidence and precise chronologic constraints, the seismogenic fault of this large event remains controversial. This work attempted to further address this issue. Based on data from unmanned aerial vehicle measurements, field investigations, analysis of typical fault profiles, and 14C dating, we determined the age of the latest slip on the Lixian-Luojiapu fault and the corresponding surface rupture range. In combination with historical earthquake data for this region, our work suggests that two sections of the Lixian-Luojiapu fault, the Tanchang-Lixian subsegment and the eastern portion of the Lixian-Luojiapu subsegment, were indeed involved in the surface rupturing of the 1654 Tianshui M8.0 earthquake. The scratches on the fault plane indicate that this seismic rupturing exhibited a left-lateral slip with a normal component and the maximum vertical displacement by this shock on the Tanchang-Lixian subsegment was 1.7±0.2 m. We suggest that the Tanchang-Lixian subsegment and the eastern portion of the Lixian-Luojiapu subsegment of the Lixian-Luojiapu fault and the West Qinling fault in the north jointly constituted the seismogenic structure of the Tianshui M8.0 earthquake based on a previous trench study. Located in the triangular zone between the Tibetan Plateau and the North China and South China blocks, tectonic stress accumulates rapidly on the Lixian-Luojiapu fault, resulting in a high potential of moderate to strong earthquakes, and this issue should be given more attention in the future.

The global and systematic coverage of Sentinel-1 radar images allows characterizing, by radar interferometry (InSAR), surface deformation on a continental scale.Our study focuses on the eastern part of the Tibetan plateau, where a combination of major strike-slip and thrust fault systems accommodates part of the deformation related to the collision between the Indian and Eurasian plates.We use an automated Sentinel-1 InSAR processing chain based on the NSBAS approach (Doin et al., 2011, Grandin, 2015) to measure the interseismic deformation across these fault systems. Processing is made on the CNES high-performance computer center in Toulouse in the FLATSIM project framework (ForM@Ter LArge-scale multi-Temporal Sentinel-1 Interferometric Measurement, Durand et al., 2019). We perform a time series analysis of the 2014-2020 Sentinel-1 InSAR data set, for 1200 km-long tracks (acquired along 7 ascending and 7 descending orbits), covering a 1 700 000 km2 area, with a 160 m spatial resolution. From about 130 acquisitions per track, we perform about 600 interferograms, with short, three months, and one-year temporal baselines. After inversion, we obtain time series of line-of-sight (LOS) delay maps, including residual atmospheric delay and network misclosure measurements. The time series are fitted by a seasonal signal plus a velocity trend. The velocity field on overlap areas agrees within less than 1~mm/yr.Finally, we decompose the LOS velocity maps into a vertical and a horizontal contribution.InSAR velocity maps highlight surface deformation patterns mostly localized on known major faults, short-wavelength patterns attributed to slope instabilities phenomena, and hydrological signals.The seasonal signal combines residual atmospheric phase delays and widespread hydrological phenomena in sedimentary basins, which we interpret in parallel with the regional geological map. Masking areas affected by dominant gravitational slope or hydrological deformation allows to better focus on tectonic deformation.We finally discuss slip partitioning on the various fault systems from the velocity maps and 2D profiles’ analysis.

Decoding the Tibetan plateau and its structural evolution has been a thorny issue for decades, triggering many controversial discussions between the proponents of the numerous key models. Numerical simulations of buoyancy forces associated with a thick crust and a low viscosity channel in the Tibetan crust predict continuous deformation, crustal uplift and thickening through an outward flow of partially molten middle/lower crust. Surface geological observations of fault systems, however, favor a model of localized deformation through the interaction between strike-slip and thrust faults. Here, we investigate the role of thrusting mechanisms involved in the plateau formation, which is essential in order to discuss these end-members competing models. We focus on the Muli thrust, a major Miocene thrust fault located at the eastern edge of the Tibetan Plateau, characterized by a pronounced topographic step of ~2000 m. We provide here an innovative quantitative approach combining thermo-kinematic modelling based on low-temperature thermochronology data, with conceptual 2-dimensional (2D) simulations of the crust’s mechanical behavior. Using the code PECUBE, we test different scenarios of rock cooling by forward modelling and inversion method in order to constrain the amount and timing of exhumation, as well as its simplified first-order crustal geometry. Given that low-temperature thermochronology data only provides the thermal history of the upper part of the crust (< 10 km), such thermo-kinematic modelling does not reveal any direct evidence of the potential implication of the lower crust. To overcome such limitations, we performed 2D mechanical modelling of the Muli thrust to constrain its mechanical behavior at the crustal scale to decipher its importance in the thickening of the plateau margin. We present here, how complementary numerical simulations based on in-situ geological observations on thrust faults, combined with thermochronology data, can be used to have a better understanding of the geological processes involved in the thickening of the Tibetan crust, and discuss both the strengths and weaknesses of such modelling.

The Xianshuihe fault in eastern Tibet is one of the most active faults in China, with the next large earthquake most likely to occur along its SE part near Kangding. Quantifying its slip rate along...

International audience; More accurate normal fault mapping and more recently constrained extension rates in southern and central Tibet allow to better discuss the mechanical processes responsible for the distribution of extension in Tibet. First, we show that the location of the rifts in southern Tibet south of the Karakorum-Jiali fault zone (KJFZ) does not exactly correspond to that of the rigid Indian lower lithosphere flattening below southern Tibet (underthrusting) inferred by P-waves global tomography, thus suggesting an absence of mechanical coupling between the two processes. Instead, E-W extension south of the KJFZ appears primarily due to divergent, orthogonal thrusting along the curved Himalayan arc, as proposed earlier. North of the KJFZ however, lower amplitude extension, distributed on numerous scattered normal faults in the western Qiangtang terrane, absorbs distributed eastward extrusion, while eastern Qiangtang is extruded more rigidly by the Xianshuihe fault, following a slip-line resulting from in-plane forces due to the collision/indenter, visible as a major discontinuity in the GPS velocity field.

International audience

Determining the timing and extent of past glaciations in Tibet is essential to reconstruct regional paleoclimate and understand how atmospheric circulation varies due to the high altitude low latitude Tibetan Plateau. In SE Tibet, geomorphological field observation of glacial deposits shows two main imbricated moraines. We apply statistical analyses to a compilation of eight new 10Be cosmogenic exposure ages from two moraine crests at GMX site and 128 previously published but recalculated exposure ages from 30 additional crests in the region. The results show that ages from the sharpest inner moraines range from 14–25 ka, corresponding to the full range of Marine oxygen Isotope Stage (MIS)-2 (i.e., Last Glacial Maximum, LGM) with less than 2% of older outliers. The outer moraines have a fundamentally different distribution with scattered ages from 10 to 200 ka, obtained using the same method of sampling, dating, and age modeling proven robust for dating the LGM inner moraines, therefore excluding a methodologic artifact. This large scatter prevents the application of any statistical analysis to the age distribution. At a site with well-developed and preserved imbricated moraines (Cuopu), the outer moraine's oldest ages are MIS-6, with the oldest one being at the MIS-6/MIS-7 limit, identical to what is observed in the regional compilation. Following our observations for the LGM moraines where

The left-lateral strike-slip Xianshuihe fault system located in the eastern Tibetan Plateau is considered as one of the most tectonically active intra-continental fault system in China, along which more than 20 M > 6.5 and more than 10 M > 7 earthquakes occurred since 1700. Therefore, studying its activity, especially its slip rate at different time scales, is essential to evaluate the regional earthquake hazard. Here, we focus on the central segment of the Xianshuihe fault system, where the Xianshuihe fault near Kangding city splays into three branches: the Selaha, Yalahe and Zheduotang faults. In this paper we use precise dating together with precise field measurements of offsets to re-estimate the slip rate of the fault that was suggested without precise age constraints. We studied three sites where the active Selaha fault cuts and left-laterally offsets moraine crests and levees. We measured horizontal offsets of 96 ± 20 m at Tagong levees (TG), 240 ± 15 m at Selaha moraine (SLH) and 80 ± 5 m at Yangjiagou moraine (YJG). Using 10Be cosmogenic dating, we determined abandonment ages at Tagong, Selaha and Yangjiagou of 12.5 ( + 2.5 / − 2.2 ) ka, 22 ± 2 ka, and 18 ± 2 ka, respectively. By matching the emplacement age of the moraines or levees with their offsets, we obtain late Quaternary horizontal average slip-rates of 7.6 ( + 2.3 / − 1.9 ) mm/yr at TG and 10.7 ( + 1.3 / − 1.1 ) mm/yr at SLH, i.e., 5.7–12 mm/yr or between 9.6 and 9.9 mm/yr assuming that the slip rate should be constant between the nearby TG and SLH sites. At YJG, we obtain a lower slip rate of 4.4 ± 0.5 mm/yr, most likely because the parallel Zheduotang fault shares the slip rate at this longitude, therefore suggesting a ∼5 mm/yr slip rate along the Zheduotang fault. The ∼10 mm/yr late Quaternary rate along the Xianshuihe fault is higher than that along the Ganzi fault to the NW (6–8 mm/yr). This appears to be linked to the existence of the Longriba fault system that separates the Longmenshan and Bayan Har blocks north of the Xianshuihe fault system. A higher slip rate along the short (∼60 km) and discontinuous Selaha fault compared to that along the long (∼300 km) and linear Ganzi fault suggests a high hazard for a M > 6 earthquake in the Kangding area in the near future, which could devastate that densely populated city.

Constraining the timing and extent of past glaciations can help understand how glaciers respond to climate change as well as study past changes in atmospheric circulation patterns, precipitation and temperature. Southern Tibet, thanks to its numerous, well-preserved, glacial deposits, is an ideal place to conduct such study, as it receives occasional winter precipitation from the mid-latitude Westerlies and abundant summer precipitation (snowfall at high elevation) from the Indian and East Asian monsoons. The fact that amounts of precipitation varied in space and time over the plateau, greatly influenced past glaciations, now recorded as successive moraine deposits. Here, we study two large moraines from the southern Yadong rift (China-Bhutan border) and determined (using 19 new 10Be cosmogenic samples) that at Jichu, which is located at the base of high summits (~7000 m), glacial deposits were abandoned during Marine oxygen Isotope Stage (MIS)-3 (~29–57 ka), and that at Qudui, located at the base of lower summits (~6000 m), the moraine was deposited during the Last Glacial Maximum (LGM, 19–26.5 ka). Both moraines directly rest on top of presumably MIS-6 (~130–191 ka) remnant surfaces. We suggest that while abundant MIS-3 precipitation allowed MIS-3 moraines to be deposited at the base of the highest summits (such as at Jichu) despite warmer temperature than during the LGM, smaller amounts of precipitation occurred during colder MIS-2, blocked by high summits, preventing deposition of large LGM moraines. By contrast, where restricted LGM precipitation can easily reach across lower summits, large MIS-2 moraines exist at their base (such as at Qudui). In addition, we compiled published ages from 22 most extensive moraines (≤MIS-6) from the northern Himalaya to central Tibet (211 samples) along three N-S transects (~50–400 km-long). We found that the relative extent of LGM and MIS-3 moraines varies between different regions, that we infer is due to spatial variations in precipitation: in general, MIS-3 (or maybe MIS-4 at places) moraines are more extensive than MIS-2 moraines, except in the Yadong rift, where LGM monsoon was able to reach, thanks to low topographic barrier and proximity to the monsoonal front. This thus allows to draw the limit of monsoonal precipitation during the LGM.

The geometry and kinematics of first-order structural systems on the Tibetan Plateau (TP) are key to understanding how the continental crust and lithosphere deformed during the India-Asia collision. The Altyn Tagh Fault (ATF), which is a large-scale fault bounding the northern edge of the Tibetan Plateau (NTP), absorbed as much as one-third of the total convergence in the collision between India and Eurasia. The Baiganhu Fault, in the western Qimen Tagh Mountains on the NTP, is recognized as belonging to the ATF and has played an important role in the development of its adjacent region. Due to the high elevation and harsh working conditions, this fault has received little attention, and the timing of its activation has not been thoroughly researched. In this study, we collected granite samples from close to the Baiganhu Fault in the Qimen Tagh Mountains, and used zircon and apatite fission track dating to constrain the timing of activation for this fault. The fission track ages and HeFTy modeling results reveal two rapid cooling stages along the Baiganhu Fault: one during the Jurassic-cretaceous (~180–120 Ma) and the second since the mid-Miocene (~15–10 Ma), consistent with other regions on the NTP. The first fast exhumation event was a far-field response to the Lhasa-Qiangtang collision, and the second stage most likely resulted from crustal thickening, with a connection to the ATF occurring at around ~15–10 Ma.

The Longmu–Gozha Co left-lateral strike-slip fault system (LGCF) is located in remote western Tibet, forming a triple junction with both the Altyn Tagh fault (ATF) and the Karakorum fault (KF), the two major strike-slip faults in the region. The Ashikule, Gozha Co and Longmu Co faults are clear and distinct left-stepping en-echelon faults, together forming the LGCF system. Although poorly documented, quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost Tibetan Plateau. Indeed, the Karakax fault (NW segment of the ATF), LGCF and KF together control the tectonics of western Tibet which itself controls the extrusion of Tibet towards the east, with the LGCF acting as a natural boundary for eastward motion of the Tibetan Plateau due to India's northward impingement. The LGCF system shows clear and impressive morphological indications of left-lateral active shear, that we quantify using field measurements (terrestrial LIDAR) along with 10 Be surface-exposure dating. Our data suggest a slip-rate 9 and > 8 mm/yr, respectively), yielding a few mm/yr of extension accommodated most likely in the Ashikule graben and surroundings, located between the ATF and Karakax faults. Numerous evidences of recent tectonic-related events are present in the vicinity, such as the 1951 volcanic eruption as well as the 2008 and 2014 Ms 7.3 Yutian earthquakes, attesting of its high activity. In addition, the LGCF's en-echelon geometry and identical direction with the ATF, as well as smaller geological offsets and lower slip-rate compared to those on the surrounding faults, suggest that this segment of the ATF may be the most recent.

The northern part of the already highly debated Karakorum fault (KF) in western Tibet (regarding its initiation age, total geological offset and slip-rate) has been argued by Robinson (2009a) and Robinson et al. (2015) to be inactive. This is based on field investigation and satellite images interpretation showing a few km of Quaternary deposits from the southern Tashkorgan basin in the Chinese Pamir, that appear undisturbed by the main branch of the KF. In particular, Robinson et al. (2015) suggested that the Kongur Shan extensional system (ICES) is not kinematically related to the KF, and that the latter is only a local fault. Here, we use basic definitions of what is an active strike-slip fault system, as well as re-emphasize the importance of the timescale of observation to discuss whether a fault is active, to demonstrate that the KF and the ICES are part of the same fault system. We argue that they together play a significant role in accommodating deformation at the western Himalayan syntaxis, under the form of extensional displacement in the Chinese Pamir. (C) 2016 Elsevier B.V. All rights reserved.

Field investigations reveal that the 2014 M w 6.9 Yutian earthquake on the left‐lateral strike‐slip Altyn Tagh fault (ATF) system, Tibetan Plateau, produced an ∼25‐km‐long surface rupture zone that contains conjugate Riedel shear faults. The coseismic surface ruptures occurred mainly along two parallel east‐northeast‐trending active left‐lateral strike‐slip faults. Rupture also occurred in a conjugate, west‐northwest‐trending zone along an active right‐lateral strike‐slip fault. The east‐northeast‐trending ruptures are concentrated in a zone of

Southern Tibet is characterized by seven main N-S trending rifts bounded by normal faults which accommodate E-W extension. Quantifying the throw and extension rates along these rifts is essential to understand their activity, onset timing, regional seismic hazard and kinematic role in the tectonic evolution of the Tibetan Plateau. The Yadong-Gulu rift (YGR), near Lhasa, is the longest and most prominent rift in southern Tibet, and one of the few that crosses the Himalayas, however it remains poorly studied and understood. Here, we focus on the Yadong rift, i.e., the southern section of the YGR, south of the Yarlung Zangbo suture. We determine the late Quaternary/Holocene throw rates at four sites, where the active Yadong normal fault vertically offsets glacial and fluvial geomorphic surfaces. Using terrestrial LiDAR, UAV and kinematic GPS, we precisely measured vertical offsets (up to 17 m) and constrained the age of abandoned surfaces using 32 10Be cosmogenic surface-exposure ages (~10–20 ka), one optically stimulated luminescence age and two travertine samples dated using U-series dating. The offset-age reconstructions yield uniform throw rates of 0.9 ± 0.3 mm/yr along the entire Yadong rift. Taking a fault dip of 50° as measured in the field, we obtain late Quaternary E-W extension rates of 0.8 ± 0.3 mm/yr, which is similar to but at the lower end of those along other rifts in southern Tibet (~1–2 mm/yr).

The 2008 Mw 7.9 Wenchuan Earthquake produced two major rupture zones: one in the Yingxiu-Beichuan fault zone (YBF) and another in the Anxian-Guanxian fault zone (AGF). A shallow trench was dug in Bajiaomiao village, Dujiangyan, Sichuan Province, which experienced a ∼4.3 m vertical offset during this large earthquake. The hanging wall of the YBF in this trench includes fault gouge and breccia. Optical microscope observations and X-ray diffraction (XRD) measurements show obvious differences between the fault gouge and breccia. Moreover, rock magnetism measurements were collected and include mass magnetic susceptibility (MS), Isothermal Remnant Magnetization (IRM), Saturation Isothermal Remnant Magnetization (SIRM), high-temperature thermo-magnetism (K–T) and magnetic hysteresis loops. Several cm-thick magnetic mineral anomalies are observed close to the Wenchuan Earthquake surface rupture zone of the YBF. Magnetite and Fe-sulfide are the main magnetic carrier materials for the fault rocks close to the surface rupture zone, including 3 cm-thick fault gouge and 3 cm-thick fault breccia, while the other fault breccia, further from the surface rupture zone, contains the paramagnetic minerals. The possible magnetic change is attributed to newly-formed magnetite from paramagnetic minerals at high temperatures (>500 °C) during the large earthquake, implying that the YBF has ever experienced high-temperature thermal pressurization earthquake slip dynamics. Moreover, the YBF has also experienced high-temperature frictional melting earthquake slip dynamics, constrained by the multiple vein pseudotachylite. These high-temperature earthquake slip processes may be responsible for the high dip angle thrust characteristic of the YBF.

Drilling in an active fault quickly after a large earthquake is an effective way to study earthquake mechanisms. In order to better understand the mechanical, physical, and chemical characteristics of the faults that ruptured during the 2008 Wenchuan earthquake (Mw 7.9), six boreholes were drilled on the two main strands (Yingxiu–Beichuan and Guanxian–Anxian faults) by the Wenchuan earthquake Fault Scientific Drilling project (WFSD). This paper focuses on the cores from the WFSD-3 borehole which drilled across the Guanxian–Anxian fault. A detailed petrological study shows that fault gouge and fault breccia are developed in the WFSD-3 cores in the Late Triassic Xujiahe Formation. The thicknesses of fault gouge range from ~1 mm to ~2.3 m. According to the characteristics of the fault rock combinations and their distribution, at least 22 subsidiary fault zones were recognized in the WFSD-3 cores. The Guanxian–Anxian fault zone is composed of fault rocks from 1192 to 1250.09 m depth, with a real thickness of ~50 m (~60 m thick in the WFSD-3 cores), and an actual damage zone of ~160 m (~980–1192 m depth in the WFSD-3 cores), and shows characteristics of multiple high-strain fault cores. The damage zone is only present in the hanging wall. The actual total thickness of the Guanxian–Anxian fault zone is ~210 m. Based on the analyses of comprehensive logging data, characteristics of the fault gouge, and seismic fault structures, the principal slip zone for the Wenchuan earthquake is identified in the black fault gouge at 1249.95 m depth in the cores, which lies almost at the bottom of the Guanxian–Anxian fault zone, and is also confirmed by surface rupture zone observations. The slip plane of the Wenchuan earthquake is a low-angle thrust fault with a dip angle of ~38° as estimated from the results of the WFSD-3 core analyses. The results from WFSD-1 showed that the Yingxiu–Beichuan segment is a high-angle thrust fault striking NW with a dip angle of ~65°. These two fault segments have different thicknesses and fault structures, which may suggest different faulting mechanisms and evolution history.

The Kongur Shan Extensional System (KES) is a ~250 km long normal fault system that bounds the Muji–Tashkorgan basin of the Chinese Pamir. It accommodates E–W extension due to the northward indentation of the Pamir salient, and its late Miocene activity has been the focus of tectonic studies. While the KES has a main normal component, ~WNW–ESE-striking segments have an additional right-lateral strike-slip component. Here, we quantify late Quaternary horizontal and vertical slip rates at three locations along the KES, where active faults cut and offset abandoned geomorphic features. We find rates of >3–4 mm a−1 (horizontal) along the western Muji fault in the north and of ~1.7 mm a−1 (vertical) and ~1 mm a−1 (horizontal) along the Kongur Shan fault in the south during the late Pleistocene. These rates are consistent with GPS and late Miocene rates, and imply that E–W extension in the Muji–Tashkorgan basin is faster in the north than in the south.

The Litang fault system that crosses the Litang Plateau, a low relief surface at high elevation (~4200–4800 m above sea level) that is not affected by regional incision, provides the opportunity to study exhumation related to tectonics in the SE Tibetan Plateau independently of regional erosion. Combining apatite and zircon fission track with apatite (U-Th)/He thermochronologic data, we constrain the cooling history of the Litang fault system footwall along two transects. Apatite fission track ages range from 4 to 16 Ma, AHe ages from 2 to 6 Ma, and one zircon fission track age is ~99 Ma. These data imply a tectonic quiet period sustained since at least 100 Ma with a slow denudation rate of ~0.03 km/Ma, interrupted at 7 to 5 Ma by exhumation at a rate between 0.59 and 0.99 km/Ma. We relate that faster exhumation to the onset of motion along the left-lateral/normal Litang fault system. That onset is linked to a Lower Miocene important kinematic reorganization between the Xianshuihe and the Red River faults, with the eastward propagation of the Xianshuihe fault along the Xiaojiang fault system and the formation of the Zhongdian fault. Such strike-slip faults allow the sliding to the east of a wide continental block, with the Litang fault system accommodating differential motion between rigid blocks. The regional evolution appears to be guided by the strike-slip faults, with different phases of deformation, which appears more in agreement with an “hidden plate-tectonic” model rather than with a “lower channel flow” model.

Using thermochronological data and thermokinematic modeling, we constrain the timing of late Miocene exhumation of the northern portion of the Gongga batholith, located in Southeast Tibet along the Xianshuihe Fault (XF). We show that rapid exhumation started in the north of the Gongga batholith at ∼9 Ma at a rate of ∼1.85 km/Myr and slowed down since ∼4 Ma. A magmatic pulse occurring during the early Pliocene (∼4 Ma) has overprinted the rapid Miocene exhumation phase in some parts of the batholith, which record mainly early Pliocene post-magmatic cooling. Slow exhumation since ∼4 Ma is consistent with the present-day lower relief observed in the centre of the batholith, which contrasts with the rugged high peaks located to the south. We propose that the northern segment of the XF, the Yalahe fault, which is not active at present, was active between 9 and 4 Ma, forming a restraining bend that focused exhumation south of it. Since ∼4 Ma, the Selaha and the Zheduotang faults form the present-day restraining bend south of which the highest part of the massif is located, including the Gongga Shan that rises more than 3000 m above the mean elevation of the plateau. In the north of the batholith, similar peaks have been removed since the Miocene by local relief reduction at high elevations. Considering that the onset of motion along the XF is contemporaneous with the onset of rapid exhumation recorded along the Kangding transect at ∼9 Ma and a total offset of ∼62 km documented for the XF, the average slip rate of the XF is ∼7 mm/yr since 9 Ma.

International audience; We present a new stratigraphy of the Jianchuan basin, one of the largest Cenozoic sedimentary basins in southeastern Tibet. This basin was regarded as recording sedimentation from the Eocene up to the Pliocene, and as such has been the focus of several studies aiming at constraining the environmental, tectonic and topographic evolution of the area. Within the Shuanghe and Jianchuan formations thirteen new zircon U/Pb ages and one biotite 40Ar/39Ar age of interbedded and cross-cutting ultrapotassic magmatic rocks show that a brief magmatic event occurred from ~ 35.7 to ~ 34.5 Ma (35.2 ± 0.4 Ma on average). The uppermost formation (Jianchuan Fm), supposedly Pliocene in age, is related to this magmatic event and is 35.4 ± 0.8 Ma old. All sedimentary formations are thus Eocene in age, with neither Oligocene nor Miocene sediments. The coal-bearing Shuanghe Formation yields a fossil of a large amynodontid typical of the Upper Eocene Ergilian interval (37.2 to 33.9 Ma). Sedimentation of the Shuanghe Formation took place in a short time interval at ~ 35.9 ± 0.9 Ma, after a large-scale drainage reorganization that induced the abandonment of a large braided-river system. This reorganization was possibly linked with the initiation of the left-lateral Ailao-Shan Red River fault and/or to widespread magmatism in the Jianchuan basin. Previous high paleoaltitude estimates for the Jianchuan basin are thoroughly re-evaluated and yield a value of 1200 ± 1200 m.a.s.l. for the Upper Eocene.

Primary rock magnetism analysis was performed on samples from the Jiulong outcrop across the Anxian–Guanxian fault of the 2008 Wenchuan Earthquake rupture zone. The protolith of hanging wall of this outcrop is the upper Triassic sediments, which formed the fault breccia and gouge by repeated large earthquakes. The footwall of this outcrop contains Jurassic grayish-green and dark-purple sandstones. The average magnetic susceptibility value of the gouge is slightly less than that of potential protolith. Based on the primary rock magnetism, the main magnetic carriers are Fe-sulfides for the gouge, magnetite for the fault breccia, and magnetite and hematite for the Jurassic grayish-green and dark-purple sandstones. Possibly during or after repeated large earthquakes (just like the 2008 Mw 7.9 Wenchuan Earthquake), it transformed the magnetic mineral from magnetite to Fe-sulfides by low thermal decomposition processes along the Anxian–Guanxian earthquake fault, which induces the slightly less average magnetic susceptibility values of the gouge than that of potential protolith. If this magnetic mineral changed only because of repeated large earthquake process, the heating by low velocity seismic slip friction and seismic fluid could possibly have been less than 300 °C. If this magnetic mineral of the Anxian–Guanxian earthquake fault is only induced after repeated large earthquakes, the earth surface process acts an important role for the magnetic mineral change. More other further studies should be done to verify the primary magnetic mineral phase change and discriminate the time of this magnetic mineral variation.

On 12 May 2008, the Wenchuan earthquake (Mw 7.9) produced complicated thrust-type co-seismic surface rupture zones, which encompass the dextral-slip thrust of the Yingxiu–Beichuan fault, the approximately pure thrust of the Guanxian–Anxian fault, and the sinistral-slip thrust of the Xiaoyudong rupture zone located between the former two. In order to understand the faulting mechanism, we discuss the rupture process by examining the segmentation and kinematics of the surface rupture zones, together with the co-seismic fault striations at various sites. Based on the two along-strike main displacement peaks (6–6.5 m and 11–12 m) and on the different geometric and kinematic patterns for the southern and northern segments of the surface rupture zones, we find that the Wenchuan earthquake might have consisted of two rupture stages, which is in agreement with seismic wave inversion results. By comparing the kinematics of fault striations occurring in the Bajiaomiao and Beichuan areas, it suggests that during the first stage, thrusting along both the Yingxiu–Beichuan fault and Guanxian–Anxian fault produced the ~ 80–100 km-long Yingxiu–Qingping surface rupture segment and the ~ 80 km-long Guanxian–Anxian surface rupture zone, respectively. Then, faulting was triggered along the Yingxiu–Beichuan fault by the first rupture process, yielding the second rupture stage, which was characterized by dextral strike-slip (or dextral oblique thrusting). Due to the overlap between the two rupture stages, the southern segment (Yingxiu–Qingping) of the Yingxiu–Beichuan rupture zone comprises two different processes while the northern segment (Gaochuan–Beichuan–Shikan) only suggests one rupture phase.

The Wenchuan earthquake Fault Scientific Drilling project (WFSD) started right after the 2008 Mw 7.9 Wenchuan earthquake to investigate its faulting mechanism. Hole 1 (WFSD-1) reached the Yingxiu–Beichuan fault (YBF), and core samples were recovered from 32 to 1201.15 m-depth. Core investigation and a suite of geophysical downhole logs (including P-wave velocity, natural gamma ray, self-potential, resistivity, density, porosity, temperature, magnetic susceptibility and ultrasound borehole images) were acquired in WFSD-1. Integrated studies of cores and logs facilitate qualitative and quantitative comparison of the structures and physical properties of rocks. Logging data revealed that the geothermal gradient of the volcanic Pengguan complex (above 585.75 m) is 1.85 °C/100 m, while that of the sedimentary Xujiahe Formation (below 585.75 m) is 2.15 °C/100 m. In general, natural gamma ray, resistivity, density, porosity, P-wave velocity and magnetic susceptibility primarily depend on the rock lithology. All major fault zones are characterized by high magnetic susceptibility, low density and high porosity, with mostly low resistivity, high natural gamma ray and sound wave velocity. The high magnetic susceptibility values most likely result from the transformation of magnetic minerals by frictional heating due to the earthquake. The YBF exposed in WFSD-1 can be subdivided into five different parts based on different logging responses, each of them corresponding to certain fault-rocks. The high gamma radiation, porosity and P-wave velocity, as well as low resistivity and temperature anomalies indicate that the Wenchuan earthquake fault zone is located at 585.75–594.5 m-depth, with an average inclination and dip angle of N305° and 71°, respectively. The fact that the fracture directions in the hanging wall and footwall are different suggests that their stress field direction is completely different, implying that the upper Pengguan complex may not be local.

Determining the slip-rate history along the right-lateral Karakorum fault (KF) is fundamental to understanding its present-day kinematic role in the deformation of Tibet. Geodetic and geologic studies suggest slip-rates of 0–11 mm/yr along this structure. Whether slip-rate variability exists along strike and/or time, or simply results from different measuring techniques/timescales, remains unknown. In order to constrain slip-rates within a timescale of 200 ka, we studied fluvial and glacial geomorphic features that are right-laterally or vertically offset by the fault by varying amounts from 7 ± 1 m to 430 ± 30 m and up to 53 ± 5 m, respectively. We constrained their ages using 10Be surface exposure dating on 141 quartz-rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the KF (Menshi–Kailas basin) and along the Gurla Mandhata detachment fault in the Pulan graben. From the 30° fault bend at Baer (80.5°E) to Mount Kailas area, the slip-rate along the KF is > 7.1+ 3.2/− 1.7 mm/yr at Menshi and > 7.9+ 3.2/− 2.5 mm/yr at Kailas (slip on two parallel fault strands). In the Pulan graben, the normal fault slip-rate is > 1.6+ 0.4/− 0.3 mm/yr. Our data suggest that the Quaternary slip-rate along the southern KF does not decrease eastward but is constant along strike for at least 200 km, from > 5–11 mm/yr in the Gar basin further north to > 7–8 mm/yr in the Menshi–Kailas basin. Because no expected along-strike slip-rate gradient is observed, it implies that the KF does not end at the Kailas but must extend where the slip rate decreases, i.e. eastward along the Yarlung Zangbo suture and southward along the Gurla Mandhata–Humla fault system.

The Litang fault system (LTFS) in the eastern Tibetan Plateau has generated several large (7.5\textgreaterM\textgreater7) historical earthquakes and has exhumed granitic peaks rising \textgreater1700 m above the mean elevation of the plateau, despite being located within a tectonic block surrounded by highly active faults. We study horizontally offset moraine crests from the Cuopu basin and a vertically offset alluvio-glacial fan from the eastern Maoya basin. We determine a left-lateral rate of 0.09 +/- 0.02 mm/yr along a slowly slipping secondary fault at Cuopu, while the main active fault at present is the normal range-front N Cuopu fault, along which we determined a left-lateral rate of 2.3 +/- 0.6 mm/yr since 173 ka. At Maoya fan, matching the vertical 12 +/- 1 m cumulative offset with the 21.7 +/- 4.2 ka fan age yields a vertical (normal) rate of 0.6 +/- 0.1 mm/yr. This rate is very similar to that recently determined at the same location using low-temperature thermochronology (0.59 +/- 0.03 mm/yr since 6.6 +/- 05 Ma). Left-lateral rates along the main faults of the LTFS range between 0.9 and 23 mm/yr at all time scales from a few years to similar to 6 Ma. The facts that the LTFS is highly segmented and that at present, the Cuopu, Maoya and South Jawa segments are mostly normal (while the Litang and Dewu segments are left-lateral/normal), could prevent the occurrence of M\textgreater7.5 destructive earthquakes along the LTFS, as is generally assumed. However, motion on the normal faults appears to be linked with motion on the strike-slip faults, potentially allowing for exceptional larger earthquakes, and implying that the area is not experiencing pure similar to NS extension but rather NW-SE left-lateral transtension. (C) 2016 Elsevier B.V. All rights reserved.

The inverse/right-lateral Yingxiu–Beichuan fault ruptured during the Wenchuan earthquake for ~ 270 km. We investigated the northeastern segment of that fault by analysing 3 newly acquired and 3 older seismic lines that cross the fault. We combine this analysis with that of the surface ruptures and of the regional geology in order to discuss the geometry, the style and the amount of motion of the fault. We conclude that the Yingxiu–Beichuan fault is very steep (~ 70°) at the surface and has still a dip > 45° at 6 km depth. The fault offsets all previous structures and particularly the Tangwangzhai nappes from which a vertical offset of 3 to 6 km is evaluated. The right-lateral component of motion along the Yingxiu–Beichuan fault appears to be larger at the surface than at depth and increases only slightly towards the NE. We suggest that the Yingxiu–Beichuan fault is continuous at depth between its northern and southern segments.

International audience; Field evidence for syn-deformation migmatization and crystallization along the Karakorum fault contradicts the study of Wang et al. (2012). The ages of such magmatic rocks provide minimum ages for the onset of deformation at similar to 23 Ma in North Ayilari and similar to 19 Ma in Tangtse. The onset of deformation at 12 Ma in the Ayilari range inferred by Wang et al. (2012) from a muscovite Ar/Ar age is a cooling age, thus only a minimum age. The similar to 60 Ma granodiorite bodies, the ophiolitic rocks and the south Kailash thrust that are correlated across the fault to provide a 52 +/- 2 km finite offset do not define reliable piercing points. Such observations as well as our previous work concur to show that the Karakorum fault initiated in the Oligo-Miocene, and has a long-term dextral slip-rate between 7.5 and 13 mm/yr, approximately twice that proposed by Wang et al. (2012).

[1] The exact location of the northern Karakorum fault (KF) in western Tibet is unclear and its current activity is debated. Here, we investigate the possible northern extension of the KF, the Muji fault, located in the Chinese Pamir, which belongs to the Kongur Shan extensional system, and provide the first quantitative estimate of its Holocene slip-rate. The fault cuts and offsets a series of 6 fluvial terraces, yielding a minimum slip-rate of 4.5 ± 0.2 mm/yr, by matching the largest terrace riser offset with its upper surface age (10Be, n = 24). Field evidences of right-lateral movement along the Kongur Shan fault, as well as geometry and kinematic similarities with the southern half of the KF attest that the Muji fault belongs to the KF system. Therefore, its fast slip-rate combined with the slow slip-rates along minor splays of the northern KF (maybe up to 4 mm/yr) southwest of the Tashkorgan basin agrees with the late Pleistocene southern KF slip-rate (>8 mm/yr).

International audience; The 400 km-­long Karakax left-­lateral strike-­slip fault is the westernmost segment of the Altyn Tagh fault. It separates northwestern Tibet to the south from the Tarim basin to the north. The western section of the Karakax fault exhibits clear co-­seismic surface ruptures of past large earthquakes. Geomorphic offset measurements from the field and high-­resolution Ikonos images along 1.5 km across the Sanshiliyingfang fan and along 55 km of the fault, range from 3 to 28 m, with distinct clusters at 6 ± 2(3), 14 ± 2, 19 ± 2 and 24 ± 3 m. The cluster of the smallest offsets around 6 m (full range from 3 to 10 m) distributed over a minimum length of 55 km, is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude Mw 7.4-­7.6 earthquake along the Karakax fault. We interpret the other offset clusters as the possible repetition of similarly sized events thus favoring a characteristic slip model for the Karakax fault. In a 3 m-­deep trench dug across the active trace of the fault we can identify the main rupture strands of the last and penultimate events. The penultimate event horizon, a silty-­sand layer, has been radiocarbon dated at 975-­1020 A.D. (AMS 14C age). It is proposed that large Mw 7.4-­7.6 events with co-­seismic slip of about 6 m rupture the Karakax fault with a return time of about 900 years implying an average slip-­rate of about 6-­7 mm/yr during the late Holocene. These results suggest that the Karakax fault is the largest left-­lateral strike-­slip fault at the rim of northwestern Tibet accommodating eastward movement of Tibet due to the India-­Eurasia collision.

International audience; This contribution provides new constraints on the timing of Tibetan glacial recessions recorded by the abandonment of moraines. We present cosmogenic radionuclide 10Be inventories at 17 sites in southern and western Tibet (32 crests, 249 samples) and infer the range of permissible emplacement ages based on these analyses. Individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10Be abundance. We consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages: 1) Erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age; and 2) Erosion progressively exposes large boulders with little prior exposure, and so the oldest sample age records the minimum moraine emplacement age. We found that depending on the scenario chosen, the moraine emplacement age can vary by > 50% for 100 ka-old samples. We consider two scaling models for estimating the production rates of 10Be in Tibet, which has an important, although lesser, effect on inferred moraine ages. While the data presented herein effectively increase the database of sample exposure ages from Tibet by 20%, we find that uncertainties related to the interpretation of the 10Be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies. A reanalysis of published data from moraines throughout Tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the Tibetan moraine age database. Thus, when viewed in a similar way with other samples collected from this area, uncertainties within moraine exposure ages obscure attribution of Tibetan glacial advances to temperature minima or precipitation maxima. Our work suggests that more reliable chronologies of Tibetan glaciations will come from improvements in production rate models for this portion of the world, as well as a better understanding of the processes that form and modify these geomorphic surfaces.

International audience; The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response, advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) highly localized deformation with the lithosphere deforming as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general. Homogeneous deformation is supported by relatively low decadal, geodetic slip-rate estimates for the Altyn Tagh and Karakorum faults. Localized deformation is supported by high millennial, geomorphic slip rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic slip-rate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip rates over various observation intervals, secular variations in slip rate appear to persist no longer than 2000 yr and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamental reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeastern edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate a significant eastward decrease in the shortening rate. This rate decrease is consistent with the transfer of slip from the Altyn Tagh fault to genetically related thrust mountain building at its terminus. Rates on the Altyn Tagh fault suggest a similar decrease in rate, but the current data set is too small to be definitive. Overall, the high, late Pleistocene-Holocene geomorphic slip velocities on the major strike-slip faults of Tibet suggest that these faults absorb as much of India's convergence relative to Siberia as the Himalayan Main Frontal Thrust on the southern edge of the plateau.

International audience; Insight into the spatial and temporal changes of slip-rate is essential to understand the kinematic role of large strike-slip faults in continental collision zones. Geodetic and geologic rates from present to several million years ago along the Karakorum fault range from 0 to 11 mm/yr. Here, we determine the first late Quaternary slip-rate at the southern end of the linear Bangong-Chaxikang seg- ment of the Karakorum fault, using cumula- tive offsets (20–200 m) of fans and terraces at three sites, as well as 74 new 10Be surface- exposure ages to constrain the age of these offset geomorphic markers. The rate is >3 mm/yr at sites Gun and Chaxikang, and it is >1.7–2.2 mm/yr at the Gar fan site. Together with rates obtained along the southernmost Menshi-Kailas segment, the Karakorum fault slip-rate seems to increase southeast- ward from south of Bangong Lake to Kailas (from >3 to >8 mm/yr). These Karakorum fault slip-rate data (>3–8 mm/yr), together with the total length of the fault (>1000 km) and its initiation age (>13–23 Ma), confirm that the Karakorum fault is the major fault accommodating dextral strike-slip motion NE of the western Himalayas. The dextral Karakorum fault in the south and the con- jugate left-lateral Longmu Co–Altyn Tagh fault system in the north are thus the major strike-slip faults of western Tibet, which con- tribute to eastward extrusion of Tibet.

Beryllium-10 surface exposure dating of offset moraines on one branch of the Karakorum Fault west of the Gar basin yields a long-term (140- to 20-thousand-year) right-lateral slip rate of approximately 10.7 +/- 0.7 millimeters per year. This rate is 10 times larger than that inferred from recent InSAR analyses ( approximately 1 +/- 3 millimeters per year) that span approximately 8 years and sample all branches of the fault. The difference in slip-rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales. Such fluctuations would be consistent with mechanical coupling between the seismogenic, brittle-creep, and ductile shear sections of faults that reach deep into the crust.

Searle and Phillips’ comment provides us with a welcome opportunity to discuss further a fundamental problem in continental collision zones, namely whether deformation is better approximated by fluid flow or block tectonics. The central issue being whether strain is localized or not on faults and shear zones, estimates of geological offsets, slip-rates, and ages of shear are the most crucial data. Searle and Phillips question the new results we present, claiming instead that: (1) Cosmogenic dating indicates slow late-Quaternary slip-rates on Asian faults (a few mm/ year or less), including the Karakorum, in conflict with early inferences [1–3]; (2) The leucogranites we

Brown et al . ([ 1 ][1]) argue that the dispersion in the exposure ages we obtained from the Manikala glacier moraines ([ 2 ][2]) is influenced by postdepositional processes and that only the oldest boulder age on each moraine group can be used to assess its abandonment age. Determining the