Search

The presence of ~NS‐trending rifts within the Tibetan Plateau attests that it is undergoing ~EW extension. In southern Tibet, the total extension rate, distributed across seven main rifts over a distance of ~1,000 km, has been inferred to amount to about half of the shortening rate across the Himalayas. Quantifying the late Quaternary extension rates across the largest rift (Yadong‐Gulu rift [YGR]) is important to understand Tibetan deformation and to discuss the high plateau evolution during the later stages of continental collision. We performed 10Be surface‐exposure cosmogenic nuclide dating of 57 samples from three fluvial surfaces and two moraines that are vertically offset by the normal faults bounding the northern YGR. After carefully assessing individual ages at each site, to elucidate scatter in the age distributions, we obtained ~EW extension rates of up to 3–6 mm/yr near the northern end of the rift (Gulu) and of only 1.3 ± 0.3 mm/yr in the south (Yangbajing). The fast rates in the north may be influenced by dextral slip along the Beng Co fault, whose rate ought to be at least 6.0 ± 1.8 mm/yr. The total late Quaternary extension rate of 9 ± 2 mm/yr we infer across southern Tibet between ~81°E and 92°E, assuming similar rates across each rift, is similar to earlier, qualitative inferences and consistent with recent geodetic results. Distinct deformation rates north and south of the Bangong‐Nujiang suture may reflect significant differences between the extensional kinematics and mechanisms across the Qiangtang and Lhasa blocks. Key Points: Extension rates along Yadong‐Gulu rift decrease from north (3–6 mm/yr) to south (~1.3 mm/yr) due to Beng Co dextral faultingThe post‐250 ka extension rate across the ~1,000 km stretch of South Tibet north of Nepal is 9 ± 2 mm/yr, consistent with geodetic ratesThe causes and mechanisms of eastward extension south and north of the Bangong‐Nujiang suture are different [ABSTRACT FROM AUTHOR]

Abstract Mountain domes rising to Is approximately equal to 6600 m along Tibet's Tanggula range herald the Eocene intrusion of calcalkaline granites into terranes accreted much earlier. Together with coeval, cogenetic volcanics, such intrusives, which have similar crystallization and cooling ages, may be part of an ESE-trending belt cutting central Tibet in half. This magmatic belt may have marked a former northern boundary of the plateau, testifying to S-directed subduction of the Asian mantle. Such subduction would have developed soon after India's collision but long before the rise of the plateau's present rims, along one of central Tibet's Mesozoic sutures. [ABSTRACT FROM AUTHOR]

In October 1862, Robert Mallet published an extensive study of a large earthquake that occurred on 16 December 1857, 150 km south-east of Naples. This event is one of the most destructive ever recorded in Italy. Although continental earthquakes of similar size are almost invariably associated with surface faulting, Mallet did not identify any surface rupture and subsequent workers have also failed to find surface traces. Using satellite images and aerial photographs as a guide, we examined two prominent Quaternary normal fault systems in the field. Flanking the Val d'Agri and the Val di Diano, both trend NW-SE and dip to the SW. The distribution of damage suggests that one or both moved in 1857. On one fault segment in Val d'Agri, we found a 2.5-m high scarp whose youthfulness and height suggest it is due to the 1857 earthquake. Comparison of the observed slip with rates derived from geomorphic evidence suggests a recurrence time for 1857 type events of about 3000 years. While the new data we provide are consistent with the event having a magnitude of Ms≈ 7.0, there are also grounds for supposing it might have been bigger. [ABSTRACT FROM AUTHOR]

Examines the growth of the plateau in Tibet, China. Morphology and age of the mountain piedmonts; Organization of late-Cenozoic faulting; Origin of the mountain ranges; Amount of late-Cenozoic crustal shortening.

Reports results of field-work in Yunnan province, China that aimed to characterize and date crustal deformation in and around the Ailao Shan and Diancang Shan mountain ranges. The Red River fault zone; Ductile, left-lateral shear in metamorphic rocks; Age of the crustal deformation; Uplift of the gneisses; Extrusion of Indochina by continental collision.

Reports on satellite observations of the Quaternary morphology of a fault at the north edge of Tibet, which shows it is very active. Evidence of offsets; Timing of offsets; Slip rates.

Although the M = w 8.7 , 1950 Assam earthquake endures as the largest continental earthquake ever recorded, its exact source and mechanism remain contentious. In this paper, we jointly analyze the spatial distributions of reappraised aftershocks and landslides, and provide new field evidence for its hitherto unknown surface rupture extent along the Mishmi and Abor Hills. Within both mountain fronts, relocated aftershocks and fresh landslide scars spread over an area of ≈330 km by 100 km. The former are more abundant in the Abor Hills while the later mostly affect the front of the Mishmi Hills. We found steep seismic scarps cutting across fluvial deposits and bounding recently uplifted terraces, some of which less than two thousand years or even a couple centuries old, at several sites along both mountain fronts. They likely attest to a minimum 200 km-long 1950 surface rupture on both the Mishmi and Main Himalayan Frontal Thrusts (MT and MFT, respectively), crossing the East Himalayan Syntaxis. At two key sites (Wakro and Pasighat), co-seismic surface throw appears to have been over twice as large on the MT as on the MFT (7.6 ± 0.2 m vs. >2.6 ± 0.1 m), in keeping with the relative, average mountain heights (3200 m vs. 1400 m), mapped landslide scar numbers (182 vs. 96), and average thrust dips (25–28° vs. 13–15°) consistent with relocated aftershocks depths. Corresponding average slip amounts at depth would have been ≈17 and ≈11 m on the MT and MFT, respectively, while surface slip at Wakro might have reached ≈34 m. Note that this amount of superficial slip would be out of reach using classic paleo-seismological trenching to reconstruct paleo-earthquake history. Most of the 1950 first arrivals fit with a composite focal mechanism co-involving the two shallow-dipping thrust planes. Their intersection lies roughly beneath the Dibang Valley, implying forced slip parallel to GPS vectors across the East Himalayan Syntaxis. Successive, near-identical, terrace uplifts at Wakro suggest near-characteristic slip during the last two surface rupturing earthquakes, while terrace boulder ages may be taken to imply bi-millennial return time for 1950-size events. As in Nepal, East-Himalayan mega-quakes are not blind and release most of the elastic, interseismic shortening that accumulates across the range. • Fresh scarps and uplifted terraces attest to >200 km-long surface rupture. • 1950 throw on the Mishmi Thrust was twice that on the Main Himalayan Frontal Thrust. • Aftershock and landslide distributions support a ≈330 km-long rupture extent. • Surface slip was as much as ≈34 m on the Mishmi Thrust. • 1950 first arrivals fit with a mechanism involving two sub-orthogonal thrust planes. [ABSTRACT FROM AUTHOR]

Fault slip rates are critical to quantify continental deformation. Those along the Karakax fault (northwestern Altyn Tagh Fault: ATF) have been debated, even though it is one of Tibet's most outstanding active faults. At Taersa, using LiDAR measurements of terrace and fan riser offsets (∼6 to ∼500 m) and 10Be/26Al dating of alluvial surfaces (<210 ka), we obtain a late Quaternary slip rate of ∼2.5 ± 0.5 mm/yr. This doubles the ∼2.6 ± 0.5 mm/yr rate time span found to the east and west. We interpret the ∼150 km‐long, free‐faced rupture along the fault to be that of the M ∼ 7.6 event felt in Hotan in 1882. Characteristic slip (∼6 m) during four large earthquakes since ∼10 ka implies a ∼2500 ± 500 years return time. A ∼3 mm/yr rate is consistent with the ∼80 km offset of the Karakax river since uplift of the West Kunlun range and sediment deposition in the Tarim foreland accelerated, ∼24 Ma ago. The faster slip rate (∼10.5 mm/yr) on the central ATF matches the sum of those along the reactivated West Tibetan terrane boundaries (Karakax and Longmu‐Gozha Co faults) at the Uzatagh triple junction (∼36°N, 83°E). The abrupt termination and altitude drop of the Karakorum range where the Longmu Co and Karakorum faults meet (Angmong junction), also reflect triple junction kinematics. Such localized changes account for the rise of the Karakorum and West Kunlun ranges and support lithospheric block tectonics rather than diffusely distributed deformation. Plain Language Summary: How the Tibetan plateau rose to ∼4500 m and deforms today remain outstanding questions. Tibet's northern edge follows the ∼2000 km‐long ATF, whose westernmost branch is the Karakax fault. Despite the spectacular escarpments and offsets observed along that fault, its slip rate, critical to quantify continental deformation, has remained controversial. Here, we corroborate that, for the last ∼210,000 years, that rate has been ∼2.5 ± 0.5 mm/yr, based on high‐resolution topography and dating of left‐laterally offset fluvial surfaces. The ∼80 km offset of the Karakax river implies that this rate may have remained constant since the rise of the Kunlun range above the Tarim basin started ∼24 Ma ago. The sharp fault trace reflects the exceptional preservation, since ∼10,000 years ago, of four M ∼ 7.6 earthquake ruptures (the last in 1882), each with ∼6 m of slip (∼2500 years return time). Fault slip rates, GPS vectors and mountain altitudes across western Tibet reflect block motions and triple junction kinematics rather than continuum deformation. Specifically, localized velocity changes appear to account for the rise of the West Kunlun and Karakorum ranges. Our results bridge the gaps between present and long‐term geological history, and broad‐scale geodesy and local field evidence. Key Points: The ∼400 km‐long, left‐lateral Karakax fault (western Altyn Tagh fault) slip rate has been ∼2.5 ± 0.5 mm/yr for ∼210 kaFour M ∼ 7.6 earthquakes (150 km rupture length; 2.5 ka return time) have offset Holocene terraces (6, 12, 18, and 24 m characteristic slip)Block tectonics and triple junction kinematics account for 24 Ma deformation of west Tibet and rise of ≥8000 m‐high Karakorum range [ABSTRACT FROM AUTHOR]

The article determines the slip-rate of the Karakorum fault to understand its kinematic role in the deformation of the Tibetan plateau. It notes that the Karakorum slip-rate is estimated to be just 1±3 millimeters/year (mm/yr), while other Quaternary geologic studies propose slip rates between 4 ±1 mm/yr and 10.7±0.7 mm/yr. Data from quartz-rich samples gathered along the Menshi-Kailas basin puts the Karakorum's current slip-rate at 10.7±0.7 mm/yr.

The article determines the slip-rate of the Karakorum fault to explain its role in the deformation of the Tibetan plateau. Based on the surface exposure ages of 127 samples taken from the right-lateral segment of the Karakorum fault and at the Pulan Graben fault in western Tibet, the slip-rate along the 30° Karakorum Fault bend at Baer to Mount Kailas varies from 5.7±3.4 - 9.4±2.5 millimeters/year (mm/yr) and the slip-rate at the Pulan Graben fault was 1.5±0.3 mm/yr.

The sources of the May 1202 and November 1759, M 7.5 Near East earthquakes remain controversial, because their macroseismal areas coincide, straddling subparallel active faults in the Lebanese restraining bend. Paleoseismic trenching in the Yammoûneh basin yields unambiguous evidence both for slip on the Yammoûneh fault in the twelfth-thirteenth centuries and for the lack of a posterior event. This conclusion is supported by comparing the freshest visible fault scarps, which imply more recent slip on the Râchaïya-Serghaya system than on the Yammoûneh fault. Our results suggest that the recurrence of an A.D. 1202-type earthquake might be due this century, as part of a sequence similar to that of A.D. 1033-1202, possibly heralded by the occurrence of the 1995 Mw 7.3 Aqaba earthquake. The seismic behavior of the Levant fault might thus be characterized by millennial periods of quiescence, separated by clusters of large earthquakes. [ABSTRACT FROM AUTHOR]

Beryllium-10 surface exposure dating of offset moraines on onebranch of the Karakorum Fault west of the Gar basin yields a long-term(140- to 20-thousand-year) right-lateral slip rate of ~10.7 ± 0.7millimeters per year. This rate is 10 times larger than that inferredfrom recent InSAR analyses (~1 ± 3 millimeters per year) thatspan ~8 years and sample all branches of the fault. The difference inslip-rate determinations suggests that large rate fluctuations may existover centennial or millennial time scales. Such fluctuations would beconsistent with mechanical coupling between the seismogenic,brittle-creep, and ductile shear sections of faults that reach deep intothe crust. [ABSTRACT FROM AUTHOR]

Teleseismic images suggest that the Tarim plate plunges ∼45°S, down to ∼300 km depth, beneath NW Tibet. The 410 km discontinuity shallows by ∼10 km under the plateau, implying ∼100°C cooler upper mantle. The deepest Moho on record (∼90 km) lies under W Qiangtang. It rises abruptly by ∼20 and ∼10 km beneath the Altyn Tagh Fault and Bangong Suture, respectively. Vp/Vs ratios are normal, except in the Yecheng flexural basin and deep under the south Karakax volcanics (∼1.92). W Kunlun’s Neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward-extruding thrust wedge of the Tarim crust. [Copyright &y& Elsevier]

Examines the faulting and earthquake triggering during the 1783 Calabria, Italy seismic sequence. Identification of three shallow shocks related to slip on the west-dipping; Comparison of damage and mesoseismal effects due to the earthquakes; Magnitudes and location of the various shocks.

Describes the fault propagation and climate control of sedimentation on the Ghoubbet Rift Floor. Organization of volcanism and platform of faulting; Decrease the rate of sedimentation; Accounts on the localization of faulting.

Presents information relating to the use of the cosmogenic surface dating on the Xidatan segment on the kunlan fault (Qinghai, China), in an attempt to determine the holocene left-slip rate. What cosmogenic dating using 26Al and 10Be in quartz pebbles constrains; Differential factors of the competing models of large-scale deformation during continental collision; How the Xidatan pull-apart trough is floored.

The northern Indian Ocean has been widely recognized as an area of broadly distributed deformation within the composite India‐Australia‐Capricorn plate, hosting several diffuse boundary zones and a diffuse triple junction. The occurrence, along reactivated fracture zones, of the exceptionally large (Mw = 8.6 and Mw = 8.2) 2012 Wharton Basin strike‐slip earthquakes, however, questions whether this composite plate is breaking apart along a discrete boundary. Using recent bathymetric and seismic data, we analyze the most prominent fracture zone (F6a), whose structural trace is particularly well expressed. We identify 60 kilometric‐scale pull‐apart basins with geometric properties (length/width ratios) similar to those observed along continental strike‐slip plate boundaries. Four of the pull‐aparts formed above narrow, subvertical faults extending into the oceanic crust. Within the broad Wharton deformation zone, the significant slip rates (0.8 to 2.5 mm/yr) and unusually large coseismic displacements recorded along F6a suggest that it may be a nascent plate boundary. Plain Language Summary: Oceanic plates are usually rigid and aseismic, except along their boundaries. In 2012, two extraordinary earthquakes with magnitudes M > 8, typical of plate boundary events, occurred in the Wharton Basin, inside the India‐Australia‐Capricorn plate, slicing the seafloor along straight, old fracture zones bearing evidence of active tectonic deformation. Using submarine relief and seismic data, we study the freshest fracture zone (F6a) to examine whether it might qualify as a nascent plate boundary between India and Australia. We find that localized cracks along it and narrow rectangular basins (pull‐aparts) resemble those along large continental strike‐slip boundary faults, supporting the inference that the composite Indo‐Australian plate is breaking apart. Key Points: Sixty kilometric‐scale pull‐apart basins show aspect ratios similar to those observed along crustal‐scale strike‐slip faultsAt least four deep pull‐aparts rooted into lithospheric faults illustrate a progressive localization of deformation along F6aSinistral slip rates <2 mm/yr and exceptionally large 2012 coseismic slip support the evolution of F6a into a nascent plate boundary [ABSTRACT FROM AUTHOR]

The Charnath Khola is a large river crossing the Himalayan thrust system in the region devastated by the great M8.3 1934 Bihar‐Nepal earthquake. Fluvial terraces are abandoned along the river and at the base of a ~20‐m high cumulative thrust escarpment. A trench across the fault scarp exposed Siwalik mudstone/siltstone overthrusting Quaternary units and three colluvial wedges interfingered with fluvial sands. The 85 accelerator mass spectrometry radiocarbon dates, from detrital charcoals sampled in the trench, a river cut and river terraces, constrain the timing of the sedimentary processes following the last two major earthquakes, in 1934 and 1255 CE. Although several samples straddle the main earthquake horizon, associating it with the 1934 earthquake, based solely on radiocarbon ages, remains challenging. The 49 detrital charcoal ages found in the pre‐earthquake and postearthquake units fall between 65 and 225 BP, a period with a flat calibration curve. Many of these radiocarbon ages are suspected to include a part due to inbuilt time (i.e., age of the wood at the time of burning), transport time, and reworking processes, which are difficult to resolve. Considering these ages at their face value could lead to dates older than the actual earthquake dates. We suggest that a part of this chronological bias is also related to a local postseismic aggradation pulse of 4 to 5 m of sediments, which is documented in the trench and terraces. This fluvial sequence, hiding the most recent surface rupture, is likely related to landslide‐sediment deposition triggered by the 1934 Bihar‐Nepal earthquake. Key Points: Evidence for 1934 and 1255 AD surface ruptures at Charnath Khola, eastern NepalAggradation pulses at the Charnath Khola follow large surface rupturing earthquakesOverlooking the predeposit processes of detrital charcoal samples could lead to paleo‐earthquake dates older than the actual earthquake dates [ABSTRACT FROM AUTHOR]

Oblique convergence across Tibet leads to slip partitioning with the coexistence of strike-slip, normal and thrust motion on major fault systems. A key point is to understand and model how faults interact and accumulate strain at depth. Here, we extract ground deformation across the Haiyuan Fault restraining bend, at the northeastern boundary of the Tibetan plateau, from Envisat radar data spanning the 2001-2011 period.We show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep-seated convergence. Mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for Synthetic Aperture Radar interferometry. The processing strategy is based on a small baseline approach. Before unwrapping, we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors. A series of filtering steps is applied to improve the signal-to-noise ratio across high ranges of the Tibetan plateau and the phase unwrapping capability across the fault, required for reliable estimate of fault movement. We then jointly invert our InSAR time-series together with published GPS displacements to test a proposed long-term slip-partitioning model between the Haiyuan and Gulang left-lateral Faults and the Qilian Shan thrusts. We explore the geometry of the fault system at depth and associated slip rates using a Bayesian approach and test the consistency of present-day geodetic surface displacements with a longterm tectonic model. We determine a uniform convergence rate of 10 [8.6-11.5]mm yr-1 with an N89 [81-97]°E across the whole fault system, with a variable partitioning west and east of a major extensional fault-jog (the Tianzhu pull-apart basin). Our 2-D model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this thrust/strike-slip fault system and demonstrates how the geometry of the Haiyuan fault system controls the partitioning of the deep secular motion. [ABSTRACT FROM AUTHOR]

The hydrological conditions during the Last Glacial Maximum in the Eastern Mediterranean have long been debated. In particular, very little is known about the development of high-altitude glaciers in this region. In the present study, morphological and sedimentological evidence, such as U-shape valleys, glacial cirques, and morainic ridges, are used to identify past glaciers on the western slopes of Mount Lebanon, which is by far the highest topography along the eastern Mediterranean coast (3088 m a.s.l.). The geometry of three paleo-glaciers is reconstructed: one 8-km-long glacial tongue stretching from the highest peak down to an elevation of about 2000 m a.s.l., and two small glacial cirques located at about 2300 m a.s.l. The age of maximum glacier advance is constrained from a 10-m-deep 36Cl depth-profile within the diamicton of one terminal moraine, and yields an early LGM timing (between 25.4 ± 3.1 ka and 31.2 ± 4.5 ka), which agrees with the chronology of the last maximum glacier extension in the Eastern Mediterranean. The three glaciers together form a consistent group, compatible with an Equilibrium Line Altitude (ELA) at 2400 m estimated using the Accumulation Area Ratio method. A degree-day model is further used to infer the temperature and precipitation conditions required to depress the LGM ELA to 2400 m. Our results suggest that the observed glacier extent is compatible with early LGM paleo-temperature records of the area only under the condition of decreased precipitation relative to modern times. These findings thus support an early LGM climate of the Levant region that was drier than today. • First evidence of LGM glaciers in the southeastern Mediterranean (Mount Lebanon; 34.25°N) are provided. • The geometry of three glaciers is reconstructed and constrains the LGM Equilibrium Line Altitude at about 2400 m a.s.l. • Glacial and climate modeling indicates a drier LGM climate than today. [ABSTRACT FROM AUTHOR]

Abstract: 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 ∼23Ma in North Ayilari and ∼19Ma in Tangtse. The onset of deformation at 12Ma 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 ∼60Ma granodiorite bodies, the ophiolitic rocks and the south Kailash thrust that are correlated across the fault to provide a 52±2km 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 13mm/yr, approximately twice that proposed by Wang et al. (2012). [Copyright &y& Elsevier]

Abstract: The M s 8.0, Wenchuan earthquake, which devastated the mountainous western rim of the Sichuan basin in central China, produced a surface rupture over 200 km-long with oblique thrust/dextral slip and maximum scarp heights of ~10 m. It thus ranks as one of the world''s largest continental mega-thrust events in the last 150 yrs. Field investigation shows clear surface breaks along two of the main branches of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping Beichuan fault, displays nearly equal amounts of thrust and right-lateral slip. Basin-ward of this rupture, another continuous surface break is observed for over 70 km on the parallel, more shallowly NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of ~3.5 m. This is one of the very few reported instances of crustal-scale co-seismic slip partitioning on parallel thrusts. This out-of-sequence event, with distributed surface breaks on crustal mega-thrusts, highlights regional, ~EW-directed, present day crustal shortening oblique to the Longmen Shan margin of Tibet. The long rupture and large offsets with strong horizontal shortening that characterize the Wenchuan earthquake herald a re-evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau, and require a re-assessment of seismic hazard along potentially under-rated active faults across the densely populated western Sichuan basin and mountains. [Copyright &y& Elsevier]

Abstract: The timing of E–W extension of the Tibetan plateau provides a test of mechanical models of the geodynamic evolution of the India–Asia convergence zone. In this work we focus on the Kung Co half graben (Southern Tibet, China), bounded by an active N–S normal fault with a minimum vertical offset of 1600 m. To estimate the onset of normal faulting we combined high and medium temperature (U–Pb, Ar/Ar) and low temperature ((U–Th)/He) thermochronometry of the Kung Co pluton, a two-mica granite of the northern Himalayan granitic belt that outcrop in the footwall of the fault. Biotite and muscovite Ar/Ar ages , are close from each other [∼16 Ma±0.2 (Ms) and ∼15±0.4 Ma (Bt)], which is typical of fast cooling. The zircon and apatite (U–Th)/He ages range from 11.3 to 9.6 Ma and 9.9 to 3.7 Ma respectively. These He ages are indicative of (1) fast initial cooling, from 11.3 to ∼9 Ma, gradually decreasing with time and (2) a high geothermal gradient (∼400 °C/km), close to the surface at ∼10 Ma. The Kung Co pluton was emplaced at about 22 Ma (U–Pb on zircon) at less than 10 km depth and 520–545 °C. Subsequent to its shallow emplacement, the pluton underwent fast thermal re-equilibration ending around 7.5 Ma, followed by a period of slow cooling caused either by the end of the thermal re-equilibration or by very slow exhumation (0.02–0.03 mm/yr) from ∼7.5 Ma to at least 4 Ma. In either case the data suggest that the exhumation rate increased after 4 Ma. We infer this increase to be related to the initiation of the Kung Co normal fault. A critical examination of previously published data show that most ∼N–S Tibetan normal faults may have formed less than 5 Ma ago rather than in the Miocene as assumed by several authors. Such a young age implies that E–W extension is not related to the Neogene South Tibetan magmatism (25 to 8 Ma). Consequently, models relating E–W extension to magmatism, such as convective removal of the lower lithosphere, may be inappropriate. We rather think that this extension is related with local accommodation of boundary forces and displacements. [Copyright &y& Elsevier]

A new detailed palaeomagnetic study of Tertiary volcanics, including extensive K-Ar and 40Ar/39Ar dating, helps constrain the deformation mechanisms related to the opening processes of the Afar depression (Ethiopia and Djibouti). Much of the Afar depression is bounded by 30 Myr old flood basalts and floored by the ca 2 Myr old Stratoid basalts, and evidence for pre-2 Ma deformation processes is accessible only on its borders. K-Ar and 40Ar/39Ar dating of several mineral phases from rhyolitic samples from the Ali Sabieh block shows indistinguishable ages around 20 Myr. These ages can be linked to separation of this block in relation to continental breakup. Different amounts of rotation are found to the north and south of the Holhol fault zone, which cuts across the northern part of the Ali Sabieh block. The southern domain did not record any rotation for the last 8 Myr, whereas the northern domain experienced approximately of clockwise rotation. We propose to link this rotation to the counter-clockwise rotation observed in the Danakil block since 7 Ma. This provides new constraints on the early phases of rifting and opening of the southern Afar depression in connection with the propagation of the Aden ridge. A kinematic model of propagation and transfer of extension within southern Afar is proposed, with particular emphasis on the previously poorly-known period from 10 to 4 Ma. [ABSTRACT FROM AUTHOR]

Discusses the determination of the Altyn Tagh strike-slip fault basin and its relationship with mountains in China. Ratio of length to width; Influence of the straight normal faults with strike-slip component on the long boundaries at the sides of the basin; Formation of the reverse thrust structures at the two sides of the center of the basin.

Examines the chronological evidence of Indo-Chinese strike-slip movement in the Altyn Tagh fault zone. Illustration on the product of the syntectonic anatexis resulting from ductile transpression; Types of zircon from mylonite; Measurement of zircon by ion microscopes.

Describes the use of frequency-time analysis on the source mechanism determination of major earthquakes in Gansu, China. Distribution of aftershocks; Calculation of depths and seismic moments; Involvement of low-frequency displacement energy on surface waves.

Assesses the accuracy and stability of earthquake relocations during the 1989 Dobi graben of the central Afar region. Inference to the Djibouti seismological network data; Elaboration of the relocation codes associated in the seismic sequence; Characterization of the seismogenic crust in the Dobi sequence.

• Tsunami earthquakes trigger oversize tsunami waves (e.g. the M w 7.8, 2010 Mentawai). • In the 2010 rupture area conjugate thrusts bound pop-ups branched on the megathrust, • Propagation of coseismic slip onto the thrusts generates extrusion of pop-ups. • Pop-up extrusion is a mechanism that efficiently generate large seafloor uplift. • We tested this mechanism by running tsunami simulations for the 2010 event. Published slip distribution models, based on geodetic, seismological and tsunami data, of the M w 7.8, 2010 Mentawai tsunami earthquake offshore south-central Sumatra, suggest that the large tsunami wave was generated by a narrow swath of high seafloor uplift along the accretionary wedge front, implying higher vertical throw than that consistent with slip on the shallow-dipping megathrust. Here we present high-resolution seismic reflection profiles across the 2010 rupture zone that image the youngest deformation at the accretionary wedge front. The profiles reveal conjugate, steeply-dipping, active thrust faults that branch upwards from the megathrust and bound triangular pop-ups. The seismologically determined co-seismic slip (≥10 m) on the 6°-dipping decollement probably caused a comparable amount of upward expulsion of these ∼3 km–wide, flat-topped pop-ups. Co-seismic throw on the ≈60° dipping thrusts that bound the pop-up plateaus maximize the uplift of the seafloor and overlying water-column, providing an additional localised tsunami source. Tsunami simulations show that such combined deformation, i.e. the broad-scale seafloor displacement caused by slip on the megathrust and the localized 8–10 m seafloor uplift across a 6–9 km-wide pop-up belt involving up to three pop-ups, is able to reproduce the 2010 tsunami amplitude measured by a DART buoy, and observed run-up heights in the Mentawai Islands. This simple mechanism, observed in analogue sandbox shortening experiments, may thus efficiently generate the oversize waves that characterize Tsunami-Earthquakes. Systematic mapping of pop-ups along accretionary wedge fronts may help identify trench segments prone to produce the special class of seismic events that spawn exceptionally large tsunamis. [ABSTRACT FROM AUTHOR]

With its central position between the Tibetan Plateau and the Tian Shan Range, the Tarim Basin is a key element of the Cenozoic Asian orogenic system. However, a comprehensive regional study, and more particularly the quantification of shortening through this basin and its margins, are still needed to understand its role in the Cenozoic deformation of Asia. From a compilation of previous works, together with an extensive dataset of satellite, field, seismic and well data, we provide a tectonic map of the Cenozoic structures and four balanced geological transects of the Tarim Basin and its surrounding ranges. Based on this map and these cross-sections, we characterize the Cenozoic deformation of the original Proterozoic Tarim block. From structural restorations and crustal budgets, we also quantify the compressive component of this deformation. Most of the Cenozoic compressive deformation (from ~94% to 100%) is concentrated in the ranges along the block margins. To the west, up to 78 ± 23 km and 54 +24/−18 km of crustal shortening are accommodated across the compressive Western Kunlun and Southwestern Tian Shan ranges, while to the east, up to 38.6 ± 18 km and 15 + 20/−15 km are accommodated across the transpressive Altyn Tagh and Southeastern Tian Shan ranges. A non-negligible amount of compressive deformation (up to ~6%) is also accommodated within the Tarim Basin by large basement-cored uplifts with a vergence synthetic to the deformation of the Tibetan Plateau edge. To the west, the Bachu uplift absorbs ~5 km of the total crustal shortening of the Western Kunlun thrust system, while to the south, the Tanan uplift accumulates ~0.6 km of the Altyn Tagh strike-slip system. Structural inheritance has a major influence on the Cenozoic deformation since ~33.3% to 100% of the total shortening is accommodated by reactivated basement structures inherited from the Protero-Paleozoic history of the Tarim block. Finally, we argue that the basement-cored uplifts in the centre of the basin imply a deformation transfer from the Tibetan Plateau to the Tian Shan, above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle. [ABSTRACT FROM AUTHOR]