Basal accretion at active subduction margins occurs through a series of tectonic slicing events at varying depths along the plate interface, shaping the forearc domain. To assess the spatial and temporal scale of the accretion-controlled forearc dynamics, it is crucial to constrain the sequence of basal-accretion episodes that form deep accretionary duplexes. This requires identifying the successive tectono-metamorphic units constituting paleo-duplexes and dating the accretion and exhumation events that expose high-pressure rocks at the surface. This first contribution of two companion papers (this issue) presents a detailed reconstruction of the tectonic and thermal structure of a high-pressure/low-temperature paleo-accretionary duplex in western Crete (Greece) that formed along the active Hellenic margin during the Oligocene-Miocene. Combining field observations, structural measurements and Raman spectroscopy on carbonaceous material (RSCM), we identify five tectono-metamorphic slices (i) bounded by shear zones often reworked during exhumation and (ii) characterized by a down-stepping of peak metamorphic temperatures towards lower structural levels. Our geological and structural mapping reveals the overall geometry of the nappe stack forming a dome-like structure, exhumed beneath major top-to-the-N and subordinate top-to-the-S detachments that accommodated N-S-directed crustal extension. This trench-perpendicular extension was intermittently rotated into an E-W direction (trench-parallel), as evidenced by a newly recognized top-to-the-W ductile-brittle detachment. Minor compressional events did not significantly alter the 3D architecture of the paleo-duplex. Reported RSCM peak metamorphic temperatures of ~350-450 °C from the nappe stack align with the typical temperature range for the downdip limit of the seismogenic zones, suggesting a first-order thermo-mechanical control on the depth of basal accretion along the subduction interface. These findings provide crucial constraints for interpreting the deep-accretion and exhumation dynamics that shaped the long-term evolution of the Hellenic forearc domain.

To understand basal-accretion dynamics in subduction zones and forearc crustal response, it is crucial to constrain the timing of slicing events forming high pressure-low temperature accretionary duplexes. This second contribution investigates the pressure-temperature-time history of tectono-metamorphic units in the paleo-duplex of western Crete, accreted along the Hellenic subduction zone during the late Oligocene-Miocene. Petrological characterization, thermodynamic modeling and a data review reveal peak metamorphic conditions evolving from 17-18 kbar and 410-430 °C to 7-8.5 kbar and 310-360 °C from top to base of the nappe stack. These results suggest a decrease in basal-accretion depth from 55-60 km to 25-30 km, likely linked to an increase in the subduction-related geothermal gradient. New Rb/Sr multi-mineral ages show a consistent decrease toward the base of the duplex, except for the lowermost Plattenkalk Unit. These ages, along with the down-stepping of peak conditions, reveal two slicing episodes between ~26 Ma and ~15 Ma, and likely three additional events from the late Oligocene to middle Miocene. (U-Th-Sm)/He thermochronology on zircon indicates rapid exhumation during the middle Miocene, with rates of ~3-11 mm/yr, decreasing to ~2-4 mm/yr at shallow levels. This dynamics was driven by the accelerating southward retreat of the Hellenic subduction, enhanced by slab tearing from ~15 Ma, contributing to the geothermal gradient increase. This study further suggests a sequence of ~2-3-Myr-long deep slicing events, providing a critical timescale for monitoring the tectonic and topographic signatures of deep mass fluxes along active margins worldwide. It also supports ongoing basal-accretion events beneath Crete, contributing to the island’s emergence.

In Northwestern South America (NWSA) geodetic observations point to a consistent northeastward displacement of blocks, while the geological record shows a predominant shortening in NW‐SE direction. Such clear evidence of strain partitioning has been extensively studied in the context of two convergent plates, but not in complex tectonic area involving several plates or tectonic blocks, such as in the northern Andes, where NWSA interacts with the Caribbean and Farallon/Nazca plates and the Panama‐Choco Arc. We propose a new deforming plate reconstruction for the region that integrates crustal deformation along the NWSA margin into a recent kinematic plate motion model in the Cenozoic. This approach enables a qualitative analysis of strain partitioning over time. Our results indicate that deformation was neither spatially homogeneous nor did it occur continuously. The main drivers of the distribution of deformation were variations of convergence obliquity, heterogeneous lithospheric strength, geometry of the subducting slabs and the transition from subduction to collisional tectonics of the Panama‐Choco Arc against NWSA. Our deforming plate model reproduces a strain‐rate evolution consistent with the different episodes of deformation reported in the region. Beyond accounting for cumulative deformation, the present‐day reconstructed velocity and strain vectors show strong agreement with modern geodetic data and earthquake focal mechanism solutions. Moreover, by integrating our reconstruction with paleoenvironmental interpretations, we propose a paleogeographic evolution of the region for the Cenozoic that closely aligns with the deformation and exhumation history of the northern Andes.

It is well known that triaxial deformation is a common feature of continental tectonics, and is accommodated by complex polymodal fault networks. Field investigations confirm that multiple phases involving time-dependent three-dimensional strain conditions (e.g. constriction, plane, and flattening strain) affect the spatial and temporal interaction of polymodal fault systems. However, a key question remains: How do changing strain conditions affect the reactivation of fault systems that formed during a previous deformation phase? Here, we conduct scaled analogue models with time-dependent boundary conditions to investigate how fault networks evolve under changing boundary conditions, including reactivation and formation of new faults.We have developed a setup in which a basal rubber sheet is stretched in one direction, so that longitudinal extension and layer thinning are accompanied by lateral shortening, hence producing triaxial deformation (Liu et al. in revision). According to previous brittle-viscous experiments with this set-up, an increase in longitudinal extension velocity results in a higher coupling between the rubber base and brittle layer, generating increasing transmission of lateral shortening from the base into the brittle layer. We thus induce constriction-to-plane strain conditions in the brittle layer as a function of longitudinal extension velocity by varying the magnitude of lateral contraction. In a new set of experiments, by varying extension velocity either stepwise or continuously, we realize time-dependent kinematic boundary conditions including deformation phases and secular changes, respectively. Digital image correlation (DIC) and photogrammetry (structure from motion, SFM) are employed to track the 3D kinematic surface and topography evolution, respectively.Preliminary observations show both the formation of new faults and the reactivation of early phase faults through a change from plane to constriction strain. Conversely, a change from constriction to plane strain conditions results in the abandonment of the early phase fault network as it becomes overprinted by fault systems of the subsequent phase. Moreover, early-phase fault systems influence the propagation and linkage of fault populations in subsequent phases. Our analogue models highlight the impact of strain conditions on the overall plan-view geometry of fault populations, providing alternative explanations for complex fault patterns and interactions (e.g. the Jeanne d’Arc basin, the North Træna Basin, and the Beagle Platform).

Extensional tectonic settings may undergo time-dependent kinematic changes, causing a multiphase evolution of the resulting fault networks. Yet, the spatial and temporal evolution of fault networks during triaxial and biaxial strain remains underexplored. Here we present scaled analogue models to investigate fault geometry, activity, and patterns across multiple phases of triaxial (constrictional) and biaxial (plane) strain. Our models show that (a) during the shift from biaxial to triaxial strain, first-phase normal faults are fully reactivated and new conjugate sets of oblique-slip faults develop during the subsequent triaxial phase. (b) During the shift from triaxial to biaxial strain, first-phase conjugate sets of oblique-slip faults either become inactive or are partly reactivated, while being cut across and linked up by new faults during subsequent biaxial strain. Our results illustrate kinematic interactions within multiphase fault networks, showing how perturbations in stress domains control the geometry of new faults and how earlier dominant faults create mechanical obstacles that hinder fault propagation. Finally, we compare the fault network evolution in our models to natural examples. The transition from biaxial to triaxial strain reflects the two-phase deformation observed in the Aegean Sea, where pre-existing normal faults were reactivated and new oblique-slip normal faults developed. Similarly, a shift from triaxial to biaxial strain explains the faulting patterns in the Barents Sea during the Late Mesozoic to Early Cenozoic, which exhibit abandoned, reactivated, and newly developed faults.

After large earthquakes, aftershocks are observed globally as a time-dependent phenomenon. In subduction zones, aftershocks occurring in the upper plate are particularly hazardous, as they often take place near densely populated areas, increasing the risk to structures already weakened by the mainshock. The number of aftershocks typically decreases over time, following a pattern described by the empirical Omori-Utsu law. Despite this well-documented behavior, the physical mechanisms driving this decay remain uncertain. While coseismic static stress transfer cannot explain the non-linear time dependence of aftershocks, transient postseismic processes such as afterslip and viscoelastic relaxation have been proposed as possible mechanisms. Alternatively, considering the temporal decay of aftershock sequences and the similar behavior observed in induced seismicity caused by wastewater injection, we explore the hypothesis that pore-pressure diffusion plays a key role in controlling the spatial and temporal distribution of natural earthquake aftershocks.In this study, we investigate the 2014 Mw 8.2 Iquique event to test our hypothesis, using an approach that integrates geodetic and seismological data, as well as geological, frictional, rheological, and hydraulic constraints. Using a 4D (space and time) modeling approach considering realistic rock material properties, we first reproduce the 3D postseismic deformation time series observed by continuous GNSS stations. We then disaggregate the individual contributions of the three dominant postseismic processes, i.e., afterslip, viscoelastic, and poroelastic relaxation, to the deformation signal. In particular, poroelastic deformation substantially affects the observed vertical geodetic signal in the near field. We then compute and analyze the spatiotemporal stress changes produced by the individual postseismic processes using the Coulomb Failure Stress (CFS) parameter. By comparing these CFS changes to the distribution of upper-plate aftershocks, we find that stress changes produced by pore-pressure changes best correlate in space with increased upper-plate aftershock activity. Furthermore, increased pore pressure reduces the effective fault normal stresses independently of the fault orientation and consequently triggers all faulting styles. This explains the higher diversity of faulting styles observed in upper-plate aftershocks. Finally, we find a very strong temporal correlation (>0.98) between the exponential increase of the cumulative number of upper-plate aftershocks and pore-pressure changes. This finding suggests that the unclear physical basis for Omori-type aftershock decay may relate to the hydraulic properties (e.g., rock permeability and porosity) of the upper plate. Thus, our work offers a deeper understanding of the hydro-mechanical behavior of the upper plate during large earthquakes and may open new avenues for physics-based aftershock forecasting.

The simplified view of the subduction interface is that of a single plane along which seismic and aseismic deformation occurs. In reality, however, exhumed subduction zones and geophysical imaging have shown that the seismogenic plate interface is a deformed, 100m-1km thick tabular region. Within this region, we currently do not know if seismic slip is localized on a single fault or distributed over several active faults, and how this impacts seismogenesis and the timing of deformation. Here, we use high-resolution earthquake locations to shed light on these questions. We focus on the aftershock sequence of the March 27th 2022, Mw 5.8 Esmeraldas earthquake which occurred at 19 km depth at the plate interface in Ecuador, and which was recorded by the dense temporary seismic network deployed during the HIPER2 marine campaign. We use machine learning to detect and pick over 1700 earthquakes (Mw 0-3), which we then locate using a double difference algorithm with cross-correlation times and a 3D velocity model. This allows us to obtain an exceptionally detailed image of the seismicity at the plate interface, which falls into a 200-400 m thick zone, comparable to plate interface thicknesses observed in exhumed subduction zones. Using a cross-correlation threshold of 0.75, we extract families of similar earthquakes, whose geometry we investigate using the 3-point method. These families generally occur on subparallel, sometimes superposed planes with a thickness of 0-40 m that is comparable to the thickness of individual fault zones observed within fossil subduction shear zones. These individual fault zones appear to form a network whose geometry impacts the aftershock expansion, itself controlled by afterslip rather than diffusive processes, thus demonstrating the importance of considering the 3D structure of the plate interface when modeling slip.

Tectonic underplating of high‐pressure/low‐temperature (HP‐LT) tectonic slices is a key mechanism in crustal growth at convergent margins. Yet, the processes controlling the geometry, depth and sequence of underplating events remain poorly constrained. We investigate the 3D petro‐structural architecture of the Phyllite‐Quartzite (PQ) nappe stack in southeastern Peloponnese (Greece), a well‐preserved segment of an Oligo‐Miocene accretionary complex within the Hellenic subduction zone, to constrain how successive pluri‐kilometric slices were formed and exhumed. Detailed structural mapping, petrology, Raman thermometry and thermobarometric modeling reveal two distinct sub‐units: Velanidhia and Pandanassa, interpreted as individual tectonic slices underplated at ∼50–60 km depth. Their pressure peak conditions (Velanidhia: 16 ± 1 kbar, 480 ± 10°C; Pandanassa: 15–18 kbar, 435 ± 21°C) and contrasted retrograde pressure‐temperature paths, witnessing post‐peak heating in Velanidhia and isothermal decompression in Pandanassa, reflect discrete underplating events under evolving thermal regimes. Geological cross‐sections and structural analysis reveal a deep paleo‐accretionary wedge geometry, involving a top‐to‐the‐E ductile‐brittle detachment that accommodated syn‐orogenic exhumation of a dome‐shaped HP‐LT nappe stack later crosscut by steep normal faults. Thanks to the detailed characterization and structural architecture of the PQ series, it is possible to constrain the trench‐parallel (≥115 km) and trench‐perpendicular (≥50 km) dimensions of each tectono‐metamorphic unit, confirming their pluri‐kilometric lateral extent. This work provides new insights into how episodic underplating at the subduction interface, witnessed by stacked tectono‐metamorphic units with contrasted P‐T evolution, governs the architecture of paleo‐accretionary wedges at active margins.

Stress distribution and creep mechanisms along modern subduction interfaces remain poorly understood, due to the lack of high-resolution constraints on the rheology of the heterogeneous plate interface and associated fluid distribution in the so-called transition zone (40-60 km depth), where deep slow slip events (SSEs) occur. Here, we document the presence of dislocation-based creep in a blueschist facies metachert block exhumed from the North Qilian paleo-subduction interface, NE Tibet. This block exhibits foliation-parallel micro-shear zones inferred to have formed under relatively fast strain rates of 10-9 s-1 and shear stresses exceeding 100 MPa. These values are paradoxical, as they are significantly higher than those estimated for the surrounding, weaker calcschist matrix, raising questions about their physical origin. We propose that the observed micro-shearing in the block, formed over a duration on the order of decades, sheds light on the local coupling induced by transient block interactions during large-scale SSEs along the deep subduction channel.

The Coastal Cordillera of Central Chile, recognized as the world's longest coastal mountain range, exhibits notable variations in erosion rates, mean precipitation, vegetation cover, and topography along its expanse. Serving as a natural laboratory, this region facilitates an in-depth exploration of the intricate interplay between tectonics and climate, owing to its distinct climate gradient and unique subduction margin features. Moreover, subduction and migration of the aseismic Juan Fernandez Ridge (JFR) from northern latitudes to its current position (~ 33.5°S) establish distinct subduction erosion conditions in the north and accretion conditions in the south of the ridge. This has implications for the tectonic deformation style of the forearc, potentially influencing the style and timing of uplift.Across the region, numerous high elevation – low relief surfaces, often surrounded by knickpoints resembling flat mountain tops, offer valuable insights into the temporal aspects of knickpoint formation hence uplift processes, which might reflect the history of the ridge subduction. Using geomorphometric indices such as steepness, chi, and knickpoint zones along rivers, we conduct a comprehensive analysis of these surfaces. Initial morphological assessments reveal no obvious trend in the distribution of these surfaces along the strike, although their size diminishes from north to south. Additionally, we used in situ cosmogenic 10Be nuclides to quantify erosion rates at five different flat mountain tops, thereby determining the knickpoint initiation time. Erosion rates are lower above knickpoint than the ones below knickpoints as expected. Consistently low erosion rates (0.004 mm/yr – 0.07 mm/yr) prevail across the region. Considering the substantial height of these surfaces (approximately 1.5-2 km), the initiation time of the knickpoints might show the history before arrival of the JFR in the south, whereas in the north they might be comparable with the passage of the JFR. However, by incorporating paleoclimate and geodynamic conditions overtime into the landscape evolution model, we anticipate obtaining more precise results for comparison. In conclusion, the Coastal Cordillera of Central Chile undergoes complex interactions among tectonics, seismology, and climate. A nuanced understanding of these processes contributes significantly to broader insights into convergent plate boundaries and the geological evolution of forearcs.

Upper-plate aftershocks following megathrust earthquakes are particularly dangerous as they may occur close to densely populated regions. Aftershock numbers decay with time, imposing a time-dependent seismic hazard that is assessed with statistical forecast models. While coseismic static stress transfer cannot explain this time-dependency, transient postseismic deformation due to afterslip, viscoelastic relaxation, and pore-pressure diffusion are potential candidates. Here we demonstrate which postseismic process is the key driver of the upper-plate aftershocks pattern following the 2014 Mw = 8.2 Iquique earthquake in northern Chile. We first use a 4D (space and time) model approach to reproduce the postseismic deformation observed in geodetic data. We then analyze the spatiotemporal stress changes produced by individual postseismic processes and compare them to the upper-plate aftershocks distribution. Our results reveal that stress changes produced by coseismically-induced pore-pressure diffusion best correlate in space and time with increased upper-plate aftershock activity. Moreover, an increase in pore-pressure reduces the three effective principal stress magnitudes likewise. Hence, all faults, regardless of their orientations, are brought closer to failure. This explains the higher diversity of the aftershocks faulting styles. Our findings provide further insights into the link between pore-pressure diffusion and upper-plate deformation in subduction zones and provide grounds for a physics-based aftershock forecast.

Subduction zones generate the largest earthquakes on Earth, yet their detailed structure, and its influence on seismic and aseismic slip, remains poorly understood. Geological studies of fossil subduction zones characterize the seismogenic interface as a 100 m-1 km thick zone1-3 in which deformation occurs mostly on metres-thick faults1,3-6. Conversely, seismological studies, with their larger spatial coverage and temporal resolution but lower spatial resolution, often image the seismogenic interface as a kilometres-wide band of seismicity7. Thus, how and when these metre-scale structures are active at the seismic-cycle timescale, and what influence they have on deformation is not known. Here we detect these metres-thick faults with seismicity and show their influence on afterslip propagation. Using a local three-dimensional velocity model and dense observations of more than 1,500 double-difference relocated earthquakes in Ecuador, we obtain an exceptionally detailed image of seismicity, showing that earthquakes occur sometimes on a single plane and sometimes on several metres-thick simultaneously active subparallel planes within the plate interface zone. This geometrical complexity affects afterslip propagation, demonstrating the influence of fault continuity and structure on slip at the seismogenic interface. Our findings can therefore help to create more realistic models of earthquake rupture, aseismic slip and earthquake hazard in subduction zones.

Along-strike seismogenic behavior of subduction megathrusts may feed back into the forearc deformation pattern as elastic and permanent deformation. The Chilean subduction zone, including the megathrust and the forearc, shows along-strike variations in both short-term behavior observed from seismicity and geodesy as well as from long-term records (upper-plate faults and topography) archived in the forearc. Unlike elastic deformation, which accumulates temporarily during the earthquake cycle, permanent deformation is reflected in the topography. Over which stage of the earthquake cycle permanent deformation occurs, however, remains unclear. Also, the connection between short-term (mainly elastic) and long-term (permanent) deformation in the forearc remains unclear.To evaluate the forearc deformation, we analyze interseismic surface deformation data of the coast and coast range (i.e., Coastal Cordillera), covering the North Chilean forearc from the south of Iquique to south of Taltal (Latitude: -20.5 to -26). We tie displacement rates obtained from five years of Sentinel-1 radar interferometric (InSAR) time series, and two view angles to a uniform reference frame spanned by accurate positioning rates and decompose the InSAR to east and vertical components. We evaluate the correlation between interseismic deformation, topography, and the activity of forearc faults. This involves an attempt to subtract the elastic vertical component, assuming a small percentage of interseismic permanent deformation. We assess the conversion of interseismic vertical deformation into permanent deformation along the coast (i.e., examining available uplifted marine terraces data) and Coastal Cordillera topography. Our preliminary findings propose a systematic change in vertical deformation from the coast to the Coastal Cordillera during the interseismic period: the coast (a narrow zone) is mainly experiencing subsidence, whereas the Coastal Cordillera is undergoing uplift. Uplift rates at the Coastal Cordillera vary along strike and are highest at the northern and southern regions of the Mejillones peninsula. Here, our elastic interface locking model fails to predict the uplift rates, implying additional processes governing uplift. Subsurface data (e.g., seismicity and seismic tomography) are required to examine the processes involved in the uplift pattern. Known as a barrier for megathrust events, the Mejillones peninsula exhibits maximum ongoing subsidence. Although interface locking is probably the primary process controlling the subsidence, our preliminary results imply the potential contribution of upper-plate faults in amplifying the subsidence rate.

Sets of marine terraces, sediments, and paleoshorelines are commonly found in forearc regions worldwide. A common assumption holds that crustal uplift prevents these features from littoral erosion. Here, we study the vertical deformation of Karpathos, a forearc island in the eastern Mediterranean, whose long axis extends at a high angle to the strike of the Hellenic Subduction System (HSS). We target three key coastal localities along the island to discuss spatial and temporal variability of vertical motion. We mapped sets of up to 19 marine terraces per locality, with elevations ranging from 1.5 to similar to 350 masl. Ages for terraces and sediments are constrained by radiocarbon (<31 masl) and Sr-isotope (2-310 masl) dating, and range from 2.4 ka to similar to 4.3 Ma. Data analysis shows that average uplift rates are up to two orders of magnitude faster over shorter (less than or similar to 100 ka) than longer (greater than or similar to 100 ka) timescales, in agreement with other local and global data sets. Further, we find evidence for multiple marine reoccupations of late Pleistocene terraces, indicating that carbonate beachrock is often resistant to multiple interactions with sea-level. Neogene marine sequences that witness longer periods (similar to 4 Ma) show signs of alternating vertical motion. Using this novel data set, we explore the effects of various mechanisms (i.e., upper-plate normal faulting, splay-thrust faulting, basal underplating) on the spatial and temporal patterns of vertical deformation. Although the contribution of each mechanism to the net vertical deformation cannot be isolated with certainty, our results show that none alone could account for the observations. Plain Language Summary In this study, we focus on understanding how the landmass of Karpathos Island, in the Hellenic Subduction System in the Mediterranean Sea, moved vertically over time. We focus mainly on marine terraces, which are wave-cut platforms near the sea forming staircase-like topography. The age of these platforms has been constrained by dating fossil shells, shell fragments, and soils that mantle the terraces: for young (closer to the sea-level) markers we used the isotope Carbon-14, while for older terraces (further inland) Strontium-87. We found that the island of Karpathos subsided prior to similar to 4.3 Ma, but since then it experiences uplift. From our analysis, we find that the vertical motion of the island is the result of, at least, three interrelated processes: (a) sediment underplating, that scrapes sediments from the down-going plate during subduction and attaches them to the base of the upper plate, pushing it upwards; (b) large earthquakes that occur either at the interface of two converging plates or on large faults that splay from this interface; and (c) smaller earthquakes produced by the horizontal stretching of the Aegean crust.

Along-strike seismotectonic behavior of subduction megathrusts feeds back into the forearc deformation as elastic and permanent deformation. However, whether and how short-term elastic deformation reflects long-term permanent deformation in the forearc and shapes the coastal region remains unclear. To evaluate the forearc deformation, we analyze the interseismic surface deformation obtained from six years of Sentinel-1 InSAR time series along the North Chilean Forearc (between 21.5°S to 26°S latitude), a hyperarid region where erosional processes masking topographic signals are minimized. To assess the conversion of interseismic vertical deformation into permanent deformation, we examine the spatial correlation between geodetic (short-term) vertical deformation and geomorphic (long-term) uplift markers and topography along the coast and Coastal Cordillera. Our findings reveal that the correlation between geodetic uplift rates and long-term uplift markers becomes neutral at the Mejillones Peninsula, suggesting localized tectonic activity. The Peninsula also separates two distinct seismotectonic segments with differing deformation patterns in the North and South. In the Northern segment, correlations and anticorrelations between geodetic uplift rates and geomorphic features imply episodic uplift, while upper plate faults exhibit less strain accumulation compared to the Southern segment and the Peninsula. The correlation variation may result from short-term, short-wavelength processes, while the consistently positive correlations with topography likely reflect long-term, long-wavelength deformation, overshadowing seismic-cycle short-wavelength deformation.

Megathrusts at convergent plate boundaries generate the largest and some of the most hazardous earthquakes on Earth. However, their physical properties, including those influencing fault slip accumulation and release and earthquake-related surface displacements, are still poorly constrained at critical depths. Here, we combine seismic imaging and geodetic modeling to investigate the structure and mechanical behavior of the Main Himalayan Thrust fault (MHT) in the center of the 2015 Mw 7.8 Gorkha rupture in Nepal. Our results from two independent observations consistently suggest the presence of a channel associated with the MHT with high compliance (shear modulus as low as similar to 4 GPa) and strain anisotropy (stiffer in the vertical orientation than in the horizontal), likely arising from a weak subducting layer with north-dipping foliation. Such mechanical heterogeneity significantly influences the quantification of short-term fault kinematics and associated earthquake potential, with implications on across-scale dynamics of plate boundaries in Himalaya and elsewhere.

Triaxial deformation is a general feature of continental tectonics, but its controls and the systematics of associated fault networks remain poorly understood. We present triaxial analog experiments mimicking crustal thinning resulting from distributed longitudinal extension and lateral shortening. Contemporary longitudinal extension and lateral shortening are related by the principal horizontal strain ratio (PHSR). We investigate the effect of crustal geometry, rheology and strain rate on deformation localization, faulting regime and pattern, and PHSR in brittle and brittle-viscous crustal-scale models. We find that in brittle models the fault networks reflect the basal boundary condition and fault-density scales inversely with brittle layer thickness. In brittle-viscous models, as strain rate (& edot;) decreases, (a) Three fault patterns emerge: conjugate sets of strike-slip faults (& edot; > 3 x 10(-4) s(-1), PHSR > 0.31), sets of parallel oblique normal faults (& edot; = 0.3-3 x 10(-4) s(-1), PHSR = 0.15-0.25), horst-and-graben system (& edot; < 0.3 x 10(-4) s(-1), PHSR < 0.1). (b) The strain localization increases systematically and gradually. We interpret the strain rate dependent of faulting regimes to be controlled by vertical coupling between the model upper mantle and model upper crust resulting in spontaneous permutation of principal stress axes. Rate-dependency of strain localization can be related to mechanical coupling between the upper and lower crust. We identify the following parameters controlling triaxial tectonic deformation: upper crustal thickness and friction coefficient, lower crustal thickness and viscosity, as well as strain rate. We test our models and predictions against natural prototypes (Tibet, Anatolia, Apennines, and Basin and Range Province) thus providing new perspectives on triaxial deformation.

AbstractUplifted Pleistocene marine terrace sequences are used to quantify uplift rates along active margins by knowing terrace age and elevation, and sea level (SL) position at the time of terrace formation. When terraces are undated, ages are assigned by correlating terraces at progressively higher elevations with progressively older highstands. Uplift at convergent margins can be constant over time or occur coseismically during upper plate earthquakes. We explore the formation of terrace sequences under conditions of constant and earthquake‐driven uplift by using a forward numerical model. The modeling reveals that terraces are generally abandoned at SL highstands but they are carved during all stands, depending on the time spent within the sea erosional‐depth‐range. Therefore sea reoccupation of a same platform after formation is a common occurrence that decreases with increasing uplift rates, suggesting that most platforms in nature may be in fact polygenetic. Furthermore, the model run time influences the terrace sequences: terraces formed at the beginning of longer runs constitute an ‘inherited morphology’ affecting subsequent sequences. When coseismic uplift is applied, the formation and preservation of terraces for a given average uplift rate depend stochastically on the coseismic displacement ‐ recurrence interval combination in relation to the SL position at the time of the earthquake. These factors significantly contribute to a higher likelihood of non‐preserved terraces along a terrace sequence, which may affect age correlation and, consequently, the resulting uplift rates. Further research is needed to explore the effect of the full seismic cycle in shaping a terrace sequence.

&lt;p&gt;The eastern Mediterranean island of Crete is located on the overriding plate of the Hellenic subduction thrust which is curved and changes strike from ~170&amp;#176; to ~50&amp;#176; in a west to east direction. Crete is located in the zone of maximum curvature of the subduction thrust. Basin and range topography together with prominent limestone scarps indicate that Quaternary deformation at the ground surface on Crete is dominated by normal faults with slip rates of up to ~1 mm/yr. These active faults comprise two primary sets that strike N-NNE (0-30&amp;#176;) and E-ESE (90-120&amp;#176;), with the more easterly faults dominating in southern Crete. Each fault set is characterised by dip slip and together they accommodate coeval W-WNW and N-NNE crustal extension. The E-ESE normal faults are approximately parallel to the strike of the subducting North African plate and form part of a regional fault system that swings in strike in sympathy with depth contours on the top of the concave northwards plate. By contrast, N-NNE normal faults are sub-parallel to the line of maximum curvature on the subduction thrust. These geometric relationships support the view that normal faulting on Crete formed, at least partly, in response to Cenozoic slab retreat (e.g., Jolivet et al., 2013), which continued into the Quaternary. In this model contemporaneous multi-directional crustal extension on Crete is driven by geologically simultaneous westward and southward retreat of the slab.&lt;/p&gt; &lt;p&gt;&amp;#160;Jolivet, L., Faccenna, C., Huet, B., Labrousse, L., Le Pourhiet, L., Lacombe, O., et al. (2013). Aegean tectonics: Strain localisation, slab tearing and trenchretreat. Tectonophysics, 597&amp;#8211;598, 1&amp;#8211;33. https://doi.org/10.1016/j.tecto.2012.06.011&lt;/p&gt;