Conference Agenda

Understanding how continental deformation partitions between distributed ductile strain and localized fault slip remains a central challenge in active tectonics and geodynamics, and it is also a key uncertainty in translating geodetic observations into seismic hazard assessments. The Tibetan Plateau – Earth’s largest region of active continental deformation – provides an exceptional natural laboratory, but until recently the spatial resolution of geodetic velocity fields has limited our ability to diagnose where strain is truly localized and where it is broadly distributed. Here we present high‑resolution geodetic velocity and strain‑rate fields for the Tibetan Plateau derived primarily from Sentinel‑1 InSAR. The results show how a small number of major strike‑slip systems exert first‑order control on the regional deformation pattern.

We processed a decade of Sentinel‑1 observations (2016–2024) as a large network of short‑baseline interferograms across 127 ascending and 114 descending frames using the COMET‑LiCSAR system and LiCSBAS time‑series methodology to estimate average line‑of‑sight surface velocities. To reduce bias from earthquake transients, we removed coseismic deformation signals for earthquakes larger than Mw 6 before calculating mean velocities. We then jointly inverted InSAR mosaics with a compilation of GNSS velocities and levelling data to solve for reference frame adjustments and a smooth 3‑D velocity field on a coarse mesh. We used the referenced ascending and descending InSAR mosaics to derive 1‑km resolution east–west and vertical velocities using the coarse model north-south component as a constraint. Our estimated velocity uncertainties are generally <2 mm/yr.

The resulting horizontal strain‑rate field is significantly sharpened by the dense spatial sampling of InSAR compared to GNSS only velocity. The data show that the highest strain rates are strongly concentrated on a few major strike‑slip fault systems, including the Altyn Tagh, Kunlun, Haiyuan, and Xianshuihe Fault Zones, which separate regions of comparatively more uniform deformation. South of the Kunlun fault, extension outpaces convergence, producing a broadly dilatational domain consistent with active east–west extension across southern and central Tibet. Vertical velocities are mostly within ±5 mm/yr and show limited correspondence with horizontal dilatation, implying that many vertical signals likely reflect non‑tectonic surface processes and/or deeper mantle contributions rather than simple isostatic responses to horizontal strain alone.

To interpret these observations, we employed a thin viscous shell geodynamic model augmented with fault‑like discontinuities, which exert resistance proportional to fault slip rate. We find that the observed deformation is best explained when major fault systems behave as relatively weak structures underlain by low‑viscosity ductile shear zones extending through the lithosphere. The models show that a weak Kunlun Fault is a key requirement that allows broadly distributed extension across southern and central Tibet. This is consistent with a potential link between Miocene Kunlun activation and the onset of rifting in north–south grabens.

Key Reference:

Wright, T.J., Houseman, G.A., Fang, J., Maghsoudi, Y., Hooper, A.J., Elliott, J.R., Evans, L., Lazecky, M., Ou, Q., Parsons, B.E. and Rollins, J.C., 2026. High-resolution geodetic velocities reveal role of weak faults in deformation of Tibetan Plateau. Science, 391(6784), pp.499-503.

Surface velocities and strain rates from satellite geodesy have become essential tools for understanding the distribution of tectonic deformation, faulting and seismic hazard. However, across large regions of distributed continental deformation, such as the Alpine-Himalayan Belt, data are only sparsely available. While previous studies have mainly used spatially sparse GNSS to measure deformation at such large scales, these approaches cannot characterize shorter wavelength features of deformation in many places. We use Sentinel-1 radar images acquired during 2016–2024 to provide trans-national average surface velocities and time series at 1 km spatial resolution stretching a distance of over 11,000 km from south-western Europe to eastern China, covering an area more than 20 million square kilometres. We produce the velocity field by combining data from over 222,000 Sentinel-1 SAR images with a new belt-wide compilation of GNSS velocities, all combined in a consistent Eurasian reference frame. Horizontal strain rates are derived from gradients of the velocity field, yielding near-continuous spatial deformation information over the entirety of the largest deforming region on the planet. The horizontal velocities and strains are dominated by tectonic deformation, which has a bimodal behaviour – focused on major faults but distributed elsewhere. Shorter-wavelength vertical velocities are dominated by non-tectonic processes, in particular the widespread over-exploitation of groundwater. Our new velocity and strain rates are foundational data sets that reveal the details of how the continents deform for the first time at trans-continental scale.

Stress perturbations generated by magmatic intrusions provide a natural laboratory for investigating how networks of shallow faults slip in response to transient loading. Interferometric Synthetic Aperture Radar (InSAR) is crucial to making detailed measurements of surface deformation to infer the patterns of fault slip and magmatic inflation. The 2024-2025 Fentale-Dofen dike intrusion episode in the Northern Main Ethiopian Rift offers a unique opportunity to investigate time-dependent stress changes and associated fault slip, as surface deformation was captured at unusually high spatial and temporal resolution by COSMO-SkyMed and Sentinel-1 satellite radar missions.

We reconstructed the evolution of deformation in an area 15 km north of the tip of the dike, where phase signals from a sequence of 8 moderate-sized earthquakes of M 4.5-6.0 can be separated from those of the dike. To achieve this, we processed COSMO-SkyMed and Sentinel-1 InSAR data to generate a network of interferograms that are inverted for displacement time-series using the Small Baseline Subset (SBAS) algorithm. We also map pre-existing and newly formed faults that slip at the surface using high-resolution Digital Elevation Models (DEM) and InSAR phase-gradient maps.

Since the deformation field exhibits high phase-gradients and discontinuous fringe patterns, standard phase unwrapping was challenging, and led to errors that bias the time-series or force the removal of valuable pixels. By inspecting individual complex interferograms and identifying unwrapping errors using the loop closure method, we corrected the unwrapping errors by masking displacement lineaments recognised as phase discontinuities in the phase-gradient maps prior to unwrapping. Using these masked interferograms led to an average network improvement of 52% in the root-mean-square misfit of loop-closure triplets after unwrapping.

We then used the improved time-series to track the deformation history of the area. By comparing a relocated catalogue of >150 moderate-sized earthquakes (M4.5-6.0) with each interferogram, we isolate time periods dominated by seismic and aseismic deformation by fitting the pixel-by-pixel time-series using a step function at the time of each significant earthquakes and a linear velocity term for interseismic periods. We used these reconstructed deformation fields to derive seismic and aseismic slip distributions and associated static stress changes on the shallow fault network. We then test whether observed slip is consistent with one or more of the following driving mechanisms: (a) a normal mainshock–aftershock sequence governed by rate-and-state friction, (b) static Coulomb stress perturbations from ongoing dike intrusions that reload fault patches, or (c) elevated pore-fluid pressure that transiently reduces effective normal stress on the faults.

Finally, we quantify the proportion of seismic and aseismic strain accommodated by pre-existing and newly formed faults during the magmatic episodes, providing new constraints on fault mechanics and their interaction with magmatic processes in active rifts.

The southern Caribbean-South America (CA-SA) transform plate boundary in northern Venezuela takes up ~22 mm/yr of dextral relative motion with strain partitioned on two sub-parallel fault systems: (1) the immediately (<5km) offshore San Sebastian Fault (SSF) and (2) the La Victoria Fault (LVF). Previous geodetic studies employing Global Navigation Satellite System measurements have found that this segment of the plate boundary is locked.

We investigated these fault systems using Sentinel-1 C-band Synthetic Aperture Radar data to yield high-resolution line-of-sight (LOS) velocities of northern Venezuela. The velocity field was created by estimating displacement time series using interferograms with long temporal (600 to 800 days) and short perpendicular (<5 m) baselines (LTSPB strategy). Velocity estimation was accomplished by fitting, to the time series, a function that accounted for seasonal variations and step artefacts introduced by unwrapping errors. The resulting LOS velocity can resolve across fault motions of 2 mm/yr.

Our time series analysis reveals complex ground deformation of the LVF onshore and variable interseismic strain accumulation of both faults. We find the LVF is a nascent right-stepping pull-apart basin with no well-defined master faults, and its development is controlled by contrasting accreted terranes. The velocity field shows that most en echelon faults of the basin are creeping, and their geometry produces both uplift (pushups) and subsidence at rates up to 10 mm/yr. The appreciable rates of ground deformation occur in the country's industrial centers, Valencia and Maracay. The LOS velocities also revealed a fault skirting the capital city, Caracas, the El Avila Fault (EAF). The fault had been previously identified, but there is no evidence of its activity. Inversion of the LOS velocities shows EAF is a thrust that divides the Caribbean Mountain range and is partially locked. Offshore, we find that most of the right-lateral SSF is locked and capable of producing a Mw 7.1 earthquake. Also, the eastern segment of the SSF (west of the EAF) accommodates dip-slip motion, suggesting that the eastern Caribbean mountain is part of an extinct pull-apart to the east, and the 220 km-long SSF has two distinct segments that might modulate maximum magnitude rupture.

In the months to years following large earthquakes, a significant amount of deformation is observed both on the faults that ruptured coseismically and in the surrounding crustal regions. Postseismic deformation can result from the relaxation of static stress changes induced by the mainshock and/or be triggered by dynamic stresses associated with the passing of seismic waves. Postseismic deformation patterns typically include seismic and aseismic slip on faults, viscous lower crust and/or upper mantle relaxation, and poroelastic deformation. Shallow postseismic creep has also been observed on secondary faults that did not rupture coseismically following the 2021 M_w 6.4 and M_w 7.1 Ridgecrest (California) earthquakes and the 2021 M_w 7.2 Nippes (Haiti) earthquake, but no evidence of similar creep events was found after other earthquakes. Here we study postseismic deformation following 3 large continental strike-slip earthquakes or earthquake sequences, including the Ridgecrest sequence, the 2021 M_w7.4 Maduo (China) earthquake and the 2023 M_w 7.8 and M_w 7.6 Kahramanmaraş (Turkey) earthquake doublet. We map the ground displacement field with InSAR time series in order to finely characterize postseismic deformation patterns. As expected for each earthquake, we observe a large-scale signal resulting from deep afterslip and viscous relaxation of the lower crust. We also observe shallow afterslip in some parts of the coseismic ruptures and on secondary faults that did not take part in the main rupture. Finally, several previously creeping landslides accelerated shortly after the Kahramanmaraş earthquakes before gradually returning to their initial creep rate over the course of months. The temporal evolution of postseismic slip both on the main fault and on secondary faults follows a logarithmic decay compatible with gradual relaxation of coseismic stress changes or previously accumulated stresses. We put our measurements of postseismic slip in perspective with interseismic slip rates and coseismic stress changes to obtain valuable insight about the rheology of these secondary faults and their role in regional tectonics. Our three case studies present variable levels of fault maturity and fault zone complexity, and comparing the extent of triggered creep on secondary faults can help better understand how strain distributes in time and space within complex fault systems.