To understand the effects of substantial topographic relief on deformation localization in the seismically active mountains, like the Longmen Shan thrust belt in the eastern Tibet, sandbox experiments were performed based on the framework of the critical taper theory. First, a reference experiment revealed that the critical taper angle was 12° for our experimental materials. Subsequently, different proto wedges (subcritical (6° in taper angle), critical (12°), and supercritical (20°)) were introduced to cover the range of natural topographic relief, and we used two setups: setup A considered only across‐strike topographic relief, whereas setup B investigated along‐strike segmentation of topography, consist of two adjacent proto wedges. In all experiments, thrust wedges grew by in‐sequence accretion of thrust sheets. Setup A revealed an alternating mode of slip partitioning on the accreted thrusts, with large‐displacement thrust and small‐displacement thrust developing in turn. And contrasting wedge evolutions occurred according to whether the proto wedge was subcritical or critical‐supercritical. In setup B, the differential deformation along the strike produced transverse structures such as tear fault and lateral ramp during frontal accretion. The observed tear fault and its associated thrust system resemble the seismogenic fault system of the 2008 Mw7.9 Wenchuan earthquake. Our experimental results could also explain first‐order deformation features observed in the Longmen Shan. Consequently, we conclude that topographic features, including topographic relief across the range and along‐strike segmentation of topography, contribute significantly to the kinematics and deformation localization in such active mountains.

No abstract

International audienceThe modern Tianshan is an active intracontinental range in central Asia. Its initial timing is poorly known and still hotly debated. As the subsidence of foreland basins is intrinsically coupled with the uplift of orogenic wedges, the foreland sedimentary records may accurately constrain the Tianshan uplifting history. To better address the question, we analyse a seismic profile across the southern Junggar foreland basin to decipher its tectonic and stratigraphic history. Four structural layers can be identified in an ascending order: the Permian - Lower Jurassic transtension-related layer, the Jurassic - Cretaceous thermal-subsistence layer, the Palaeogene layer and the Miocene - Quaternary foreland sedimentary layer. The oldest sedimentary sequence in the foreland succession is of the Shawan Formation deposited at ~24 Ma based on magnetostratigraphic constraints. This indicates that foreland deformation in the northern Tianshan and uplifting of the modern Tianshan probably initiated at the beginning of the Miocene

The intracontinental earthquake behavior is not well understood due to its complexity in the interior of the continent. The Tianshan Mountain is located in the interior of the Eurasian plate, which was rejuvenated in the Cenozoic due to the India‐Asia collision and sourced several large earthquakes. The 2016 Hutubi earthquake occurred within the northern Tianshan, China, during rupture of a high‐angle back‐thrust toward the hinterland, which broke the long‐time quiescence in the mountain front. The geometry, dynamics, and hazard implications of this earthquake on an out‐of‐sequence thrust fault remains unclear. The 3‐D structural model shows that the coseismic fault is connected to the large‐scale blind Southern Junggar thrust, which sourced the 1906 Mw ~8 Manas earthquake. The geometry of the coseismic fault and the occurrence of extensional tectonics in the Jurassic suggest that the Hutubi earthquake occurred on a reactivated rift‐related structure. To test this hypothesis and study the kinematics, we performed sandbox modeling, with results suggesting that coseismic fault can form during positive inversion of a preexisting Jurassic rift, and that the Southern Junggar thrust and related structures may be recently active. Coal beds facilitated the transfer of fault slip and strain from mountain to basin and from basal to roof detachment. We propose that the preexisting rift and related sedimentation controlled the subsequent structure and geomorphology of the mountain belt through thrust wedge formation. This study provides a typical example for the study of intracontinental inversion structure and its earthquake behavior.

Three-dimensional (3D) modeling and restoration are powerful in describing the geological characteristics and kinematics which cannot be fully accomplished by the two-dimensional modeling methods. In this study, we applied 3D modeling and restoration to the Beisantai anticline along the mountain front of the Northern Tianshan. The Beisantai anticline shows an EW-trending structure in the shallow layers with NS-trending structures in the deep layers. The 3D seismic reflection data visualize the growth strata well, which record the evolution of the anticline and the influence of Cenozoic India-Asian collision. Our results suggest that a combination of multiple deformations of this anticline on different layers developed during different episodes. In addition, multiphase deformation and strain distribution along the eastern part of the northern Tianshan was implied. Combined with an analysis of the burial and hydrocarbon-generating history from borehole data, we proposed new potential