The experimental study of interactions between tectonics and surface processes is an ambitious challenge, requiring the development of specific analog materials capable of jointly simulating geomorphological and crustal deformation processes. In this work, we refined the physical and mechanical properties of the MAT-IV analog material to improve morphological rendering and extend its range of application. We halved the average particle size (D50) of the granular mixture and added a fifth component (pumice powder), which increased the material’s erodibility and allowed the precipitation rate controlling exogenous surface processes to be reduced by a factor of three. We performed a dozen experiments to explore different compositions and determine a standard formula through morphometric analyses. The new material, MAT-V, allows for reproducing better-scaled morphologies and represents a significant upgrade over MAT-IV. Scaling analysis and morphometric measurements lead to the recommended composition: 37.5% silica microbeads (1–50 µm grain size), 37.5% silica powder (1–80 µm grain size), 15% PVC powder (5-85 µm grain size), 10% pumice powder (1–150 µm grain size), < 1% anthracite (0–200 µm grain size). Using an average cyclic rainfall rate of 5–10 mm/h, a spatial scaling of 1 cm = 100 m and 1 s = 5 years are considered relevant to model relief dynamics under temperate to sub-tropical climatic conditions. To constrain the key parameters governing model surface dynamics, we implemented a joint modeling approach combining experimental and numerical modeling. This allowed us to quantify geomorphological parameters, including the slope (n) and discharge (m) exponents, hillslope erodibility (Khill), critical slope (SC), and effective settling velocity (VS).

The Earth surface, where life develops and stands, is strongly affected by denudation which is the sum of physical erosion and chemical weathering. Denudation impacts soil formation and agriculture, affects the relief stability and, at the geological time scale, controls the atmospheric CO2 via the weathering of silicates and the production of sediments that later bury organic matter in the oceans. In the context of global warming, it is particularly important to predict how denudation will change and hence impact the Earth Surface where we live. This requires to understand the links between past climate variability and denudation changes, especially during the Quaternary when Earth experienced rapid climate oscillations of amplitude similar to what is expected in the future due to anthropic impact. To reach this goal, quantitative estimate of past denudation rates during the Quaternary are needed. In this study, we reconstruct Quaternary paleo-denudation rates in the Tianshan range located in Central Asia because (1) it is a major orographic barrier that likely played an important role during the onset of Quaternary glaciations, (2) regional climate variations have been well documented by the geochemical and isotopic analyses of speleothems in caves and (3) well dated Quaternary deposits are abundant in the piedmonts To reconstruct basin average paleo-denudation rates we used the inherited 10Be concentrations derived from the inversion of 10Be cosmogenic depth profile collected across abandoned alluvial surfaces. We used a unique inversion technique to reprocess preexisting data and also analyze 5 new cosmogenic depth profiles located in the northern Tianshan. In this region, to extend the dataset we have also collected 9 ancient river sand samples along the magnetostratigraphically dated Jingou He section. For comparison between all data, paleo-denudation rates are normalized to modern 10Be derived denudation rates across the same drainage basin. This yields to a 0-1.5Ma record of paleo-denudation rates that is compared to climate variations to discuss the potential links between the two.

Predicting how denudation will change in the future, and hence impact the Earth's surface, requires an understanding of the links between past climate variability and denudation responses, especially during the Quaternary. In this study, we reconstructed Quaternary paleo-denudation rates in the eastern Tianshan range (central Asia) and compared the results to climate changes documented by geochemical variations recorded in nearby speleothems. Based on a reanalysis and inversion of 18 published cosmogenic in situ Be-10 depth profiles collected across abandoned Quaternary alluvial surfaces, combined with analyses of five new profiles in the northern Tianshan piedmont, we constrained the inherited Be-10 paleo-concentrations and when the surfaces were abandoned. To extend the dataset beyond the Mid-Pleistocene Transition, when important changes in denudation are hypothesized to have occurred, we also collected nine ancient river sand samples along the Jingou He section in the northern Tianshan, previously dated by magnetostratigraphy to similar to 1.5 to similar to 1 Ma. To calculate paleodenudation rates based on the measured paleo-concentrations, we used both uncorrected cosmogenic paleoproduction rates (assuming no ice in the drainage basin) and rates corrected for maximum ice cover extent. Paleo-denudation rates were then normalized to modern values derived from in situ Be-10 cosmogenic concentrations previously measured in modern river sand. We observed steady Early Pleistocene denudation rates similar to those at present day in the Jingou He basin. However, since 700 ka during the Middle Pleistocene, paleo-denudation rates were more variable, but uncorrelated with climate oscillations. Those variations may have been due to climatic cooling and a stronger glacial influence that had a nonlinear effect on denudation, yielding spatial variations between drainage basins. However, we see no sustained acceleration in denudation despite the increased amplitude of glacial cycles during the Late Pleistocene.

New satellite geodetic data challenge our knowledge of the deformation mechanisms driving the active deformations affecting southeastern Sicily. The PS-InSAR (Permanent Scatterer Interferometry Synthetic Aperture Radar) measurements evidence a generalized subsidence and an eastward tilting of the Hyblean Plateau, combined with a local relative uplift along its eastern coast. To find a mechanical explanation for the present-day strain field, we investigate short- and large-scale surface-to-crustal deformation processes. Geological and geophysical data suggest that the southward migration of the Calabrian subduction could be the causative geodynamic process. We evaluate this hypothesis using flexural modeling and show that the combined downward pull force, induced by the Ionian slab roll-back and the overloading of the Calabrian accretionary prism, is strong enough to flex the adjacent Hyblean continental domain, explaining the measured large-scale subsidence and eastward bending of the Hyblean Plateau. To explain the short-scale relative uplift evidenced along the eastern coast, we perform elastic modeling on identified or inferred onshore and offshore normal faults. We also investigate the potential effects of other deformation processes, including upwelling mantle flow, volcanic deflation, and hydrologic loading. Our results enable us to propose an original seismic cycle model for southeastern Sicily, linking the current interseismic strain field with available long-term deformation data. This model is mainly driven by the southward migration of the Ionian slab roll-back which induces a downward force capable of flexuring the Hyblean crust.

Better understanding of stress perturbations, strain propagation and fluid flow in the upper crust require characterisation of fault damage zone evolution. Outcrop studies help understand the different processes operating during fault movement; but capture little about the evolution through time. In this study, we investigate damage zone evolution using high-resolution analogue modelling; simulating the growth of a normal fault population. The incremental strain reveals that early deformation stages occur by strain localisation into corridors of distributed deformation. Active deformation within these corridors becomes narrower as segment linkage occurs, leading to the formation of master faults, encouraging further localisation of incremental strain. This results in wide zones of cumulative strain around the fault, accommodated by different types of fault damage geometry, which formed at very different stages of the fault system growth. We also highlight the new concept of "fault system damage", that shows similarities with observations in nature. These first descriptions of the fault damage evolution allow an understanding of the composite content of damage zones. This gives support to assess zones of permeability enhancement in naturally fractured reservoirs, and proposes a view of damage distribution for targeting fluid flow, geothermal resources, leaks, micro/macro seismicity and mechanical properties of fault zones.

The Tianshan mountains have complex and variable topography and documenting their growth is important for understanding both intracontinental mountain building and the evolution of the global climate. We investigate whether this topography is in equilibrium with crustal influx (thickening) and sediment outflux (denudation). Based on literature, we estimate that the eastern Tianshan has been subject to a total crustal shortening rate of-9.4 mm/a across the Kuitun-Kuche transect, implying-1.3 mm/a of crustal thickening and a total crustal influx of-9 x 107 m3/a. We measured in-situ cosmogenic 10Be concentrations in modern river sands of 34 catchments to constrain recent (0-6 ka) basin-averaged denudation rates within the range and on its two flanks. Denudation rates range from 0.020 +/- 0.002 to 0.53 +/- 0.07 mm/a, averaging 0.20 +/- 0.04 and 0.11 +/- 0.02 mm/a in the north and south, respectively; these rates correspond to respective total sediment outfluxes of (542 +/- 69) x 104 and (164 +/- 24) x 104 m3/a. To ensure that these values can be compared to Pleistocene tectonic rates, we reconstructed Pleistocene denudation rates in seven of the studied basins. For this, we determined inherited in -situ cosmogenic 10Be concentrations from 11 cosmogenic depth profiles of abandoned fluvial terraces deposited in the Tianshan piedmonts. These data indicate that denudation rates have been relatively steady since the Pleistocene and thus that recent and Pleistocene sediment fluxes can be compared. These results show that crustal thickening outpaced denudation and sediment outflux by a factor of-10. Therefore, the Tianshan topography is not in dynamic equilibrium and is growing, even if materials are being subducted into the mantle. Consequently, to sustain this disequilibrium, the range grew laterally. This lateral growth and the inheritance of structures and basins are likely responsible for the complex topography of the range.

The study of faults in the upper crust has generated interests in modelling their impact on fluid flow and the mechanical behavior of the earth's crust. Fault damage zones are important structures with multiple implications for resource management and earthquake studies. This work aims to characterize the distribution and growth of damage around faults, and to study its impact on the Displacement - Damage thickness (D-T) scaling law. Two complementary approaches of field analyses and analog modelling of normal faults are developed to answer this question. We presents new results of fault damage mapping, D-T scaling in carbonate rocks and the first analog modelling experiments of fault damage zones inspected in-plane. The results show a heterogeneous and asymmetric distribution of damage around faults, mainly influenced by fault interactions during their growth (segmentation, conjugate faults). A D-T law specific to wall damage is established and shows a normal correlation between D and T for less than c. 100 m of fault displacement, and also confirms the existence of a damage thickness threshold after c. 100 m of displacement. To explain this law, we propose a damage zone growth model controlled by the interaction and coalescence of fault segments. Analogue modelling shows a failure mode transition during fault growth, from a segmented dilatational-shear mode to a localized compactional-shear mode. They also demonstrate that initiation of segmentation, segment activity selection, interaction and coalescence processes control the development of fault damage zones and the D-T law. Furthermore, the thickness of the faulted brittle layer is a main controlling parameter of segmentation, strain localization and the fault damage thickness threshold observed.

A better understanding of stress perturbation around faults, strain propagation, and fluid flow in the upper crust require characterization of the evolution of fault damage zones. Numerous studies provide significant amounts of data and description from a broad variety of faults, however, fault damage evolution is not clearly understood.In this study, we investigate experimentally damage zones dynamic evolution during normal faults population growth. With this aim, we used a sandbox type device and multilayered analog model, monitored by high-resolution cameras. Several types of damage zones are evidenced and we performed an accurate description of their growth from initiation to mature damage. New damage types including conjugate link damage and graben damage are described for the first time and show similarities with observations in nature. We highlight the new concept of “fault system damage” as the increase of deformation and secondary fault density by the interaction of major faults. We also show that fault damage zones grow by segment linkage into corridors of fault segments formed in the first stages of model deformation. Based on these observations, we propose and discuss the new concept of “segment selection in corridors” as the process of the onset of fault maturation and their damage zone development.

The goal of the ERC funded FOCUS project is to study an active fault offshore Catania using fiber optics, sea-floor geodesy, seismological stations (onshore and OBS on the seafloor) and detailed in-situ observations using an ROV and an AUV. Here, we report on the latter. In October 2020 using the ROV Victor6000 and in January 2022 using the AUV IdefX, we performed micro-bathymetric mapping (at an altitude of 50 m above the seafloor) of a 15-km-long segment of the North Alfeo Fault, covering water depths of about 1600 m to 2300 m. A prominent lozenge-shaped transpressive ridge or “pop-up” type structure is one of the primary features of this portion of the fault zone. It forms a flat-topped plateau culminating at about 1700 m water depth. It is cross-cut by a network of N-S striking faults resembling domino blocks or books in a book-shelf.Sub-bottom profiling (using a chirp system on the AUV IdefX at an altitude of 70 m above the seafloor) crossed the transpressive ridge and imaged the network of narrowly spaced (typically 100 - 200 m spacing) N-S striking faults, which are steeply W dipping normal faults. This suggests the transpressive ridge is currently collapsing. Indeed, the eastern part of the plateau is marked by a small (600 m long from headscarp to toe) submarine landslide. The overall pattern in the northern portion of the mapped area (west of the plateau) is a series of oblique secondary faults, crossing the primary fault at an angle of about 30°. Using a very simple analog model of a thin layer of cohesive granular material above two rigid plates, with a slightly curved fault track, it was possible to produce a primary strike-slip fault directly above the cut between the two plates, and several distinct transpressional ridges (pop-ups) as well as transtensional fissures or gashes. Secondary faults form obliquely to the primary fault and are oriented at about a 30° angle clockwise from the trend of the primary fault. This pattern reproduces the large-scale features observed in the micro-bathymetry from the NW prolongation of the North Alfeo fault. A series of analog experiments using different rheologies in the sediment layer is planned in the future to test the likely detachment (nucleation) depth for the strike-slip fault in the basement.

The Multi-scale Laboratories (MSL) are a network of European laboratories bringing together the scientific fields of analogue modeling, paleomagnetism, experimental rock and melt physics, geo- chemistry and microscopy. MSL is one of nine (see below) Thematic Core Services (TCS) of the European Plate Observing System (EPOS). The overarching goal of EPOS is to establish a compre- hensive multidisciplinary research platform for the Earth sciences in Europe. It aims at facilitating the integrated use of data, models, and facilities, from both existing and new distributed pan European Research Infrastructures, allowing open access and transparent use of data. The TCS MSL network allows researchers to collaborate with other labs and scientists. By becoming part of the rapidly growing TCS MSL network, new laboratories are offered a platform to showcase their research data output, laboratory equipment and information, and the opportunity to open laboratories to guest researchers through the Transnational Access (TNA) program. The EPOS Multi-scale laboratories offer researchers a fully operational data publication chain tailored to the specific needs of laboratory research, from a bespoke metadata editor, through dedi­ cated, (domain­specific) data repositories, to the MSL Portal showcasing these citable data publica- tions. During this process the data publications are assigned with digital object identidiers (DOI), published with open licenses (e.g. CC BY 4.0) and described with standardized and machine-read- able rich metadata (following the FAIR Principles to make research data Findable, Accessible, Interoperable and Reusable. The TCS MSL is currently working on linking these data publications to the EPOS Central Portal1, the main discovery and access point for European multi-disciplinary data, and on increasing the number of connected data repositories.

The Quaternary geodynamics of the Central Mediterranean region is controlled by the migration of narrow orogenic belts within the slow Nubia‐Eurasia plate convergence. As testified by the occurrence of major volcanic and seismic events, the Eastern Sicilian Margin is presently one of the most active regions. Using a Permanent‐Scatterer approach, we process Sentinel‐1 satellite images acquired from 2015 to 2020 to provide an island‐wide quantification of surface displacements at a high spatiotemporal resolution. We then convert the calculated mean surface velocities along the ascending and descending satellite line of sight into the ITRF2014 reference frame by using GNSS velocity data derived from regional stations. The resulting pseudo‐3D velocity field mainly highlights a general uplift of about 1.5 ± 0.5 mm/yr of the Nebrodi‐Peloritani range and its differential motion with respect to mainland Sicily along the Cefalù‐Etna seismic zone. Permanent/Persistent‐Scatterer (PS) vertical velocities in the Eastern Hyblean region reveal a long wavelength eastward downbending of the margin, including the inferred epicentral area of the 1693 Noto earthquake. Compared to Quaternary coastal uplift rates, these results confirm the relative low activity of Western Sicily, a potential slow uplift of South‐Central Sicily and a significant discrepancy along the Eastern Hyblean margin were PS‐derived vertical velocities that appear 2–3 mm/yr lower than the Quaternary rates. Over the 2015–2020 timespan, transient processes are also captured, notably on Mount Etna, showing both magmatic pressurization uplift and collapse of the eastern flank, but also all over Sicily where numerous gravitational mass movements and anthropogenic ground subsidence are detected.

Surface topography results from complex couplings and feedbacks between tectonics and surface processes. We combine analog and numerical modeling, sharing similar geometry and boundary conditions, to assess the topographic evolution of an alluvial fan crossed by an active thrust fault. This joint approach allows the calibration of critical parameters constraining the river deposition–incision laws, such as the settling velocity of suspended sediments, the bed-rock erodibility, or the slope exponent. Comparing analog and numerical models reveals a slope-dependent threshold process, where a critical slope of ca. 0.081 controls the temporal evolution of the drainage network. We only evidence minor topographic differences between stable and stick-slip fault behavior localized along the fault scarp. Although this topographic signature may increase with the slip rate and the return period of slip events, it remains slight compared to the cumulated displacement along the fault scarp. Our results demonstrate that the study of morphology cannot be used alone to study the slip mode of active faults but can be a valuable tool complementing stratigraphic and geodetic observations. In contrast, we underline the significant signature of the distance between the fault and the sediment source, which controls the degree of channels incision and the density of the drainage network.

Since the Neogene, the Central Mediterranean geodynamics is controlled by the migration of narrow orogenic belts, driven by fast slabs retreat, and the slowly converging Nubian and Eurasian plates. Nowadays, the Calabrian Arc continues its southeast migration in response to the Ionian oceanic plate rollback but at a much slower rate. The Sicilian kinematics has reached a transient state between the ending subduction-collision phase that formed the island, and the steady-state convergence between Africa and Eurasia. This setting explains why Sicily is among the most seismically active region of the Mediterranean, gathering the most destructive historical events recorded in Italy, such as the Noto (1693, Mw ∼ 7.4) and Messina earthquakes (1908, Mw ∼ 7.1). Such tectonic activity has led to numerous studies aimed at evaluating current surface motions at a regional scale using GPS networks. To improve the spatial coverage, we built the first 3D geodetic velocity field over the whole Sicily Island by processing from the Sentinel-1 InSAR time-series. Averaged velocities along the ascending and descending satellite line-of-sight (LOS) were obtained using the Permanent-Scatterer approach (PS-InSAR) over the 2015-2020 period. We converted PS velocity fields into the Nubia reference frame, with the ITRF2014 vertical reference, by adjusting PS to 3D-GPS mean velocities. Reliable GPS velocities were retrieved from time-series of the MAGNET GPS network, leading to about 40selectedsitescoveringSicily and south-west Calabria. Onalltracks, theagreementbetweenPSandGPSLOSvelocitiesisexcellent (rms < 1mm/yr), and derived orbital corrections are robust, except for the western descending track that is only constrained by five GPS data. Since the projected north-south GPS velocity difference along the LOS is about 0.5 mm/yr, we assumed that thenorth-componentoftheground displacementisnegligible. By reducing the problem to a 2D estimation(East and Up component) and using both ascending and descending LOS velocities, we derived the East-andUp-component of the ground deformation within the Nubia-ITRF2014 reference frame. Uncertainties are estimated in the order of 1mm/yr. The results show that the Up-component is consistent with previous works indicating a significant uplift of the Peloritani range (~ 1±0.5 mm/yr) in north-eastern Sicily. Together with the East-component, the whole Peloritani block appears, however, as a coherent tectonic unit and does not show any dislocation along the Tindari line, as suggested by previous structural field observations. Interestingly, PS-InSAR data evidence an eastward tilting of the Hyblean Plateau, with about 1.5 mm/yr of subsidence of the Augusta bay relative to the Vittoria plain, and a 1 to 2 mm/yr of differential vertical motion along the southern coast, between Agrigento and the Licata and Sciacca locations. Although the reconstructed ground motion only captures a short time-window of the seismic cycle, these data represent a major milestone to evaluate the seismic hazard of Sicily.

Fault damage zones strongly influence fluid flow and seismogenic behavior of faults and are thought to scale linearly with fault displacement until reaching a threshold thickness. Using analog modeling with different frictional layer thicknesses, we investigate damage zone dynamic evolution during normal fault growth. We show that experimental damage zone growth with displacement is not linear but progressively tends toward a threshold thickness, being larger in the thicker models. This threshold thickness increases significantly at fault segment relay zones. As the thickness threshold is approached, the failure mode progressively transitions from dilational shear to isochoric shear. This process affects the whole layer thickness and develops as a consequence of fault segment linkage as inferred in nature when the fault matures. These findings suggest that fault damage zone widths are limited both by different scales of mechanical unit thickness and the evolution of failure modes, ultimately controlled in nature by lithology and deformation conditions.

Tectonic inversion of passive margins is a common but poorly documented process preceding subduction inception. We perform here a comprehensive land‐sea experimental modeling of this key process by reproducing the morphotectonic and sedimentary evolution of the central Algerian margin over the last 6 Myr. Our approach is based on scaled analog models integrating interactions between crustal shortening and surface processes, including erosion, water transport, sedimentation, gravitational instabilities, and base‐level changes. A challenge was to simulate the effects of the Messinian Salinity Crisis (MSC) through a major sea‐level oscillation and halite deposition. By using realistic boundary conditions, adapted analog material, and robust, first‐order parameters for physiography setups, we successfully reproduce the morphotectonic domains and the time‐dependent geometrical relationships between fluvio‐deltaic sedimentary systems, erosional surfaces, and thrust faults as observed since Messinian times. Our results highlight (1) the key role played by the MSC sea‐level oscillation on an ultra‐fast building, destruction and re‐sedimentation of fans and deltas from the upper slope to the abyssal plain; (2) the development of a large popup structure subparallel to the coastline, with progressive strain migration from the backthrust on land toward a frontal thrust of opposite vergence at mid‐slope and the margin toe; and (3) the importance of lateral changes in initial wedge shape and strain distribution for determining the non‐cylindrical geometry of the margin and progradation of piggy‐back basins during tectonic inversion. Our results support that the central Algerian margin is witnessing the early building of an accretionary wedge combining thin‐skinned and thick‐skinned tectonic styles.

We have developed a scaled analog model of a subduction zone simulating seismic cycle deformation phases. Its rheology is based on multilayered visco‐elasto‐plastic materials to account for the mechanical behavior of a continental lithospheric plate overriding a subducting oceanic plate. The seismogenic zone displays unstable slip behavior, extending at depth into a weak interface with stable slip properties. The model succeeds in reproducing interseismic phases interrupted by coseismic ruptures and followed by after‐slip. The experimental data catalog shows a broad variability of slip events from aseismic slow slips to fast dynamic lab quakes. Results also show the occurrence of both isolated and precursory slow‐slip events arising before the mainshocks. Given the absence of fluids in the model, the broad variability in slip event velocity can be attributed to fault roughness complexity. The model rheology induces also a key visco‐elastic coupling between the elastic overriding plate and the mantle wedge allowing, for the first time, to reproduce experimentally a realistic postseismic visco‐elastic relaxation phase. Preliminary results reveal that the tectonic loading rate modulates this visco‐elastic coupling. A low loading rate weakens it, which increase the amount of storable interseismic elastic deformation, and favors the occurrence of large megathrust events. A high loading rate strengthens it, which minimize the accumulation of interseismic elastic deformation, the slip‐event sizes, and promote aseismic creep. This new scaled‐analog subduction model is a complementary tool to investigate earthquake mechanics and improve the interpretation of geodetic and seismological records.

Faults form dense, complex multi‐scale networks generally featuring a master fault and myriads of smaller‐scale faults and fractures off its trace, often referred to as damage. Quantification of the architecture of these complex networks is critical to understanding fault and earthquake mechanics. Commonly, faults are mapped manually in the field or from optical images and topographic data through the recognition of the specific curvilinear traces they form at the ground surface. However, manual mapping is time‐consuming, which limits our capacity to produce complete representations and measurements of the fault networks. To overcome this problem, we have adopted a machine learning approach, namely a U‐Net Convolutional Neural Network (CNN), to automate the identification and mapping of fractures and faults in optical images and topographic data. Intentionally, we trained the CNN with a moderate amount of manually created fracture and fault maps of low resolution and basic quality, extracted from one type of optical images (standard camera photographs of the ground surface). Based on a number of performance tests, we select the best performing model, M Ref , and demonstrate its capacity to predict fractures and faults accurately in image data of various types and resolutions (ground photographs, drone and satellite images and topographic data). M Ref exhibits good generalization capacities, making it a viable tool for fast and accurate mapping of fracture and fault networks in image and topographic data. The M Ref model can thus be used to analyze fault organization, geometry, and statistics at various scales, key information to understand fault and earthquake mechanics.

In this study, we reconstruct the Miocene to Quaternary shortening history across the Qiulitag anticline, a complex fault-bend fold located in southern Tianshan. We studied the Yaha and Kuche sections, where we combined surface structural measurements and seismic imaging to model the stratigraphic horizons. The history of folding was reconstructed based on magnetostratigraphic analyses and eight cosmogenic burial ages in Kuche. Pleistocene deformation rates were also quantified in Yaha based on a deformed fluvial terrace that we dated to similar to 67 ka using a cosmogenic depth profile. Our results suggest that the fold grew at a mean slip rate of 0.9-1.3 mm/a in both sections but accelerated to similar to 2.5 mm/a during the Pleistocene in Kuche. These results support a migration of the deformation towards the basin during the Pleistocene and suggest that most of the present deformation in the Tianshan is accommodated across the external structures of the range.