Mathilde Radiguet

Understanding the mechanisms controlling deformation localization is crucial for our understanding of fault mechanics and improving seismic hazard assessment, but has not been extensively studied for normal‐faulting earthquakes. Here, we present a thorough analysis of the 2016 Mw 6.5 Norcia, Italy, earthquake using high‐resolution satellite geodesy. We investigate the degree of deformation localization, evaluate its controlling factors and the link with the distribution of slip with depth. Using the optical image correlation technique with an innovative method for noise correction, we measure the near‐field 3D displacements associated with the Norcia event. Based on these measurements, we quantify the amount of off‐fault deformation (OFD) and evaluate how it varies with external factors. We find 46 (25 cm) of OFD on average and a strong correlation with local topographic slope and near‐surface lithology, with increased distributed deformation where ruptures traverse unconsolidated sediments and areas of gentler slopes. In contrast, the correlation between OFD and the fault segment orientation relative to the regional stress field is weak. We develop a comprehensive slip model accounting for complex multi‐segmented fault geometry, topography, and 3D elastic structure through a joint inversion of optical, InSAR, and GPS data. The inversion reveals a highly heterogeneous slip distribution characterized by large slip (up to 3.5 m) at depth, and several shallow slip patches. We find a pronounced average shallow slip deficit (SSD) of 73, with no along‐strike correlation between SSD and OFD. This suggests that the OFD primarily reflects surficial inelastic processes occurring within the shallow soil.

Understanding and modeling the deformation following large earthquake is essential for characterizing the rheological structure and processes that release post-seismic stress. Here, we measured postseismic deformation over an 8-year period following the 2014 M_w8.1 Iquique earthquake using Sentinel-1 InSAR and GNSS time series in northern Chile and Bolivia. We jointly modeled the surface displacements caused by afterslip and viscoelastic relaxation using a two-dimensional finite element model. The combination of GNSS and InSAR data allows us to continuously map the temporal and spatial variations of the displacement field, especially in the vertical component, providing valuable constraints for modeling the rheological structure of the continental plate from the slab to the Altiplano. The amplitude of the uplift pattern claims for a weak zone below the western part of the Altiplano, where the volcanic arc is fed by partial melting. To reproduce the temporal evolution of post-seismic uplift, this weak zone must be governed by a Burgers rheology, combining a transient Kelvin body with a viscosity η_Kwz = 2 × 10¹⁸ Pa.s and a Maxwell body with a viscosity η_Mwz = 2 × 10¹⁹ Pa.s. To the west, our preferred model includes a cold nose rooting into the slab at a slab-mantle decoupling depth of d_CN = 84 km. This near-trench elastic wedge, predicted by thermal models, drives mantle flow and generates surface uplift during post-seismic relaxation. By characterizing the post-seismic deformation field following the Iquique earthquake, our results refine the rheological structure below the Central Andes and define its response to stress changes down to short time scales.

Understanding and modeling the deformation following large earthquake is essential for characterizing the rheological structure and processes that release post-seismic stress. Here, we measured postseismic deformation over an 8-year period following the 2014 M_w8.1 Iquique earthquake using Sentinel-1 InSAR and GNSS time series in northern Chile and Bolivia. We jointly modeled the surface displacements caused by afterslip and viscoelastic relaxation using a two-dimensional finite element model. The combination of GNSS and InSAR data allows us to continuously map the temporal and spatial variations of the displacement field, especially in the vertical component, providing valuable constraints for modeling the rheological structure of the continental plate from the slab to the Altiplano. The amplitude of the uplift pattern claims for a weak zone below the western part of the Altiplano, where the volcanic arc is fed by partial melting. To reproduce the temporal evolution of post-seismic uplift, this weak zone must be governed by a Burgers rheology, combining a transient Kelvin body with a viscosity η_Kwz = 2 × 10¹⁸ Pa.s and a Maxwell body with a viscosity η_Mwz = 2 × 10¹⁹ Pa.s. To the west, our preferred model includes a cold nose rooting into the slab at a slab-mantle decoupling depth of d_CN = 84 km. This near-trench elastic wedge, predicted by thermal models, drives mantle flow and generates surface uplift during post-seismic relaxation. By characterizing the post-seismic deformation field following the Iquique earthquake, our results refine the rheological structure below the Central Andes and define its response to stress changes down to short time scales.

Understanding and modeling the deformation following large earthquake is essential for characterizing the rheological structure and processes that release post-seismic stress. Here, we measured postseismic deformation over an 8-year period following the 2014 M_w8.1 Iquique earthquake using Sentinel-1 InSAR and GNSS time series in northern Chile and Bolivia. We jointly modeled the surface displacements caused by afterslip and viscoelastic relaxation using a two-dimensional finite element model. The combination of GNSS and InSAR data allows us to continuously map the temporal and spatial variations of the displacement field, especially in the vertical component, providing valuable constraints for modeling the rheological structure of the continental plate from the slab to the Altiplano. The amplitude of the uplift pattern claims for a weak zone below the western part of the Altiplano, where the volcanic arc is fed by partial melting. To reproduce the temporal evolution of post-seismic uplift, this weak zone must be governed by a Burgers rheology, combining a transient Kelvin body with a viscosity η_Kwz = 2 × 10¹⁸ Pa.s and a Maxwell body with a viscosity η_Mwz = 2 × 10¹⁹ Pa.s. To the west, our preferred model includes a cold nose rooting into the slab at a slab-mantle decoupling depth of d_CN = 84 km. This near-trench elastic wedge, predicted by thermal models, drives mantle flow and generates surface uplift during post-seismic relaxation. By characterizing the post-seismic deformation field following the Iquique earthquake, our results refine the rheological structure below the Central Andes and define its response to stress changes down to short time scales.

Understanding and modeling the deformation following large earthquake is essential for characterizing the rheological structure and processes that release post-seismic stress. Here, we measured postseismic deformation over an 8-year period following the 2014 M_w8.1 Iquique earthquake using Sentinel-1 InSAR and GNSS time series in northern Chile and Bolivia. We jointly modeled the surface displacements caused by afterslip and viscoelastic relaxation using a two-dimensional finite element model. The combination of GNSS and InSAR data allows us to continuously map the temporal and spatial variations of the displacement field, especially in the vertical component, providing valuable constraints for modeling the rheological structure of the continental plate from the slab to the Altiplano. The amplitude of the uplift pattern claims for a weak zone below the western part of the Altiplano, where the volcanic arc is fed by partial melting. To reproduce the temporal evolution of post-seismic uplift, this weak zone must be governed by a Burgers rheology, combining a transient Kelvin body with a viscosity η_Kwz = 2 × 10¹⁸ Pa.s and a Maxwell body with a viscosity η_Mwz = 2 × 10¹⁹ Pa.s. To the west, our preferred model includes a cold nose rooting into the slab at a slab-mantle decoupling depth of d_CN = 84 km. This near-trench elastic wedge, predicted by thermal models, drives mantle flow and generates surface uplift during post-seismic relaxation. By characterizing the post-seismic deformation field following the Iquique earthquake, our results refine the rheological structure below the Central Andes and define its response to stress changes down to short time scales.

The deformation regime that accommodates tectonic motion at plate boundaries changes as pressures and temperatures increase with depth, transitioning from the shallow frictional sliding of seismic ruptures to deep, viscous flow. We use recurring swarms of low-frequency earthquakes in this transition zone to measure the recurrence intervals and durations of accompanying slow slip across four plate boundaries. We find these time scales systematically decrease with depth and linearly scale with one another. Assuming a transition zone governed by episodic faulting, the observed time scales produce an average slow slip rate of 7 ± 2 mm/d across all four plate boundaries that is independent of depth. Thermal models place these slow slip dynamics within a common, narrow range of temperatures. Our results suggest deep slow slip is the result of the episodic unjamming of the plate boundary by frictional heterogeneities whose relaxation is modulated by surrounding temperature-dependent viscous material.

Les observations récentes ont mis en évidence la diversité des régimes de glissement des failles, et particulièrement l'existence de glissements asismiques transitoires, les séismes lents. Ce travail a pour objectif la compréhension de l'impact de ces séismes lents sur le cycle sismique. La zone étudiée correspond à la zone de subduction du sud du Mexique, au niveau de la lacune sismique de Guerrero. A partir de mesures de déplacement de surface, principalement par GPS, le glissement sur l'interface de subduction est modélisé par des dislocations dans un milieu élastique. Cette analyse nous permet de contraindre l'évolution spatio-temporelle de deux épisodes de glissements lent (2006 et 2009-2010), ainsi que le couplage de l'interface de subduction. Nos résultats montrent une certaine variabilité dans l'évolution spatio-tempororelle des deux glissements étudiés : le séisme lent de 2006 présente clairement une propagation du glissement, à une vitesse d'environ 1 km/jour ; le séisme lent de 2009-2010 présente deux sous-évènements, l'occurrence du deuxième sous-évènement étant liée au déclenchement par le séisme de Maule au Chili. Nos résultats mettent également en évidence les variations latérales dans le couplage intersismique de l'interface de subduction : le couplage dans la lacune sismique de Guerrero étant 4 fois plus faible que le couplage de part et d'autre de la lacune. Ainsi la majeure partie du glissement est accommodée par les séismes lents dans la lacune sismique de Guerrero.

The Séchilienne landslide in the French Alps is a large, deep-seated landslide whose dynamics are strongly influenced by local hydro-geological conditions. The highly fractured moving zone has a higher hydraulic conductivity than the underlying stable bedrock, creating a perched aquifer. Below, the bedrock hosts a deep saturated zone. Between 2011 and 2016, the landslide underwent an active phase marked by an initial increase and a subsequent decrease of displacement rates. Since then, the landslide has remained largely stable. The site has been instrumented with a seismic network since 2012 [1], providing a unique opportunity to link relative seismic velocity changes to hydro-geological observations and landslide deformation. We use ambient seismic noise interferometry to compute depth-dependent relative seismic velocity changes (dV/V), reflecting variations in the elastic properties of the landslide.We observe clear seasonal cycles in seismic velocities within the shallow, fractured part of the landslide. Velocities decrease during periods of elevated groundwater levels and increase during dry conditions, indicating a reversible response to water-table fluctuations in the perched aquifer. Superimposed on this seasonal behavior, dV/V shows a long-term trend during the active phase of the landslide. At shallow depths, dV/V decreases during periods of increasing displacement rates and increases as displacement rates decrease. At greater depths in the deep aquifer, dV/V decreases during the deceleration phase. During the stable period, dV/V shows almost no long-term trend. This behavior indicates sensitivity of dV/V to landslide kinematics and a possible coupling between the shallow and deep aquifers.The results show that seismic interferometry captures both short-term hydrologically driven variations and longer-term changes connected to landslide kinematics, showing distinct responses at different depths. The approach provides valuable insight into hydromechanical processes governing landslide evolution and highlights the potential of continuous seismic monitoring for slope stability assessment.[1] Seismic data have been acquired by the French National Landslide Observatory (OMIV), and are available at doi.org/10.15778/RESIF.FR and doi.org/10.15778/RESIF.MTWe acknowledge help from the ISTerre-SIG team for operating the seismic network. We acknowledge the support of the European Research Council (ERC) under the grant agreement no. 101142154 (Crack The Rock).