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SUMMARY The Ganaveh earthquake on 2021 April 18 (Mw 5.8) occurred in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran, as a mainly compressive event. The InSAR coseismic displacement maps reveal a maximum of 17 cm of surface displacement in the satellite line of sight direction. InSAR inversion indicates a low-angle NE-dipping causative fault plane with a maximum slip of 95 cm at ∼6 km depth. It highlights the occurrence of the Ganaveh earthquake within the competent layers of the Zagros sedimentary cover, beneath the Gachsaran formation. A slight sinistral slip component (2.9 cm) is retrieved which is compatible with the USGS focal mechanism. Time-series analysis of SAR images after the main shock until the end of 2021 indicates a maximum of 7 cm of post-seismic surface displacement with a similar strike and pattern as the coseismic phase. This similarity and the distribution of aftershocks suggest an afterslip mechanism for the post-seismic phase. The inversion of post-seismic cumulative displacement evaluates a maximum of 30 cm slip at a depth of ∼5 km along the coseismic causative fault. A regional compressional stress regime (N041°E for the direction of the σ1 stress axis) is constrained by using the focal mechanisms of 39 earthquakes occurring between 1968 and 2021, including the Ganaveh main shock and its five larger aftershocks. Applying this direction of compression on the Ganaveh fault plane also results in a minor sinistral movement, consistent with the geodetic results. The relocated main shock and aftershocks as well as our InSAR coseismic displacement situations on the hanging wall of the Zagros Foredeep fault highlight it as the causative fault of the Ganaveh earthquake. To fit the geometry of the Ganaveh rupture plane with the Zagros Foredeep fault, we modelled a listric fault plane and its slip distribution using the available geological data. The retrieved slip variation on the listric plane is in close agreement with the slip pattern on the modelled planar geometry. The low dip angle of the rupture plane combined with a listric geometry highlights the thin-skin characteristics of the Zagros Foredeep fault as the causative fault of the Ganaveh earthquake. The occurrence of this moderate magnitude earthquake on the Zagros Foredeep fault underlines its role as the western structural boundary for the recurrence of Mb > 5 events in the Dezful embayment.

During the RESOLVE project ("High-resolution imaging in subsurface geophysics: development of a multi-instrument platform for interdisciplinary research"), continuous surface displacement and seismic array observations were obtained on Glacier d'Argentière in the French Alps for 35 days in May 2018. The data set is used to perform a detailed study of targeted processes within the highly dynamic cryospheric environment. In particular, the physical processes controlling glacial basal motion are poorly understood and remain challenging to observe directly.Especially in the Alpine region for temperate based glaciers where the ice rapidly responds to changing climatic conditions and thus, processes are strongly intermittent in time and heterogeneous in space. Spatially dense seismic and GPS measurements are analyzed applying machine learning to gain insight into the processes controlling glacial motions of Glacier d'Argentière.Using multiple bandpass-filtered copies of the continuous seismic waveforms, we compute energy-based features, develop a matched field beamforming catalogue and include meteorological observations.Features describing the data are analyzed with a gradient boosting decision tree model to directly estimate the GPS displacements from the seismic noise.We posit that features of the seismic noise provide direct access to the dominant parameters that drive displacement on the highly variable and unsteady surface of the glacier. The machine learning model infers daily fluctuations and longer term trends. The results show on-ice displacement rates are strongly modulated by activity at the base of the glacier. The techniques presented provide a new approach to study glacial basal sliding and discover its full complexity.

The motion of glaciers with a temperate base is highly variable in time and space, mainly as a result of glacier basal sliding being strongly modulated by subglacial hydrology. Although transient friction laws have recently been established in order to predict short-term sliding velocity changes in response to water input changes, yet little observations enable fully constraining these laws. Here we investigate short-term changes in glacier dynamics induced by transient rainwater input on the Glacier d’Argentière (French Alps) using up to 13 permanent GPS stations. We observe strong surface acceleration events materialized by maximum downglacier velocities on the order of 2 to 3 times background velocities and associated with significant glacier surface uplift of 0.03 m to 0.1 m. We demonstrate that uplift strikingly coincides with water discharge. In contrast, horizontal speed-up occurs over a timescale shorter than discharge and uplift changes, with a maximum occurring concomitantly with maximum water pressure but prior to maximum discharge or uplift. Our findings suggest that transient acceleration and uplift of the glacier are not necessarily modulated by the same mechanism. We also observe that the horizontal speed-ups propagate downglacier at migrating speeds of 0.04 m s-1 to 0.13 m s-1, suggesting an underlying migration of subglacial water flows through the inefficient, distributed system. We demonstrate that the temporal relationship between water discharge, water pressure, and three-dimensional glacier motions are complex and cannot be directly interpreted by changes in the subglacial water pressure through cavity formation and water storage.

The 2013 April 16 Mw 7.7 Saravan earthquake, an intra-slab earthquake with a normal faulting mechanism, occurred in the Makran subduction zone, where the Arabian oceanic lithosphere subducts northward under Iran and Pakistan. To examine the postseismic displacement of the Saravan earthquake, we processed one ascending (A13) and one descending track (D122) from 2014 to 2022. We construct 1000 and 504 interferograms for ascending and descending tracks, respectively. We remove the topographic and flatten-earth phase contributions using the 30 m Shuttle Radar Topography Mission Digital Elevation Model and precise orbital parameters. We correct the turbulent component of the tropospheric delay using atmospheric parameters of the global atmospheric model ERA-Interim provided by the European Center for Medium‐range Weather Forecast. Then, we filter the generated interferograms using Goldstein’s filter and unwrapped them with a branch-cut algorithm. Once all interferograms are corrected and unwrapped, we employ an SBAS time-series analysis based on the phase evolution through time for each pixel, to retrieve the mean velocity map and displacement through time. The mean velocity map in the LOS direction indicates a sharp signal close to the Saravan earthquake suggesting that the observed signal belongs to the postseismic phase of this event. The postseismic spatial profile derived from high-quality time series analysis of Sentinel 1-A images has the opposite pattern of displacement with respect to the coseismic profile derived from Radarsat-2 interferograms. Due to the 50-80 km depth of the earthquake, observing such a deformation approximately seven years after the earthquake is interesting and consequently, we decided to study it in detail.Large earthquakes are usually followed by transient surface deformation which reflects the rheology of the lithosphere and sub-lithospheric mantle following three mechanisms: afterslip, viscoelastic relaxation, and poroelastic rebound. In this study, we investigate the responsible mechanism of Saravan 2013 postseismic deformation through the before mentioned mechanisms. Due to the opposite sense of deformation during co and postseismic periods, we first try to assess the viscoelastic relaxation mechanism using the PSGRN/PSCMP code. We calculate the time-dependent green functions of a given layered viscoelastic-gravitational half-space for our dislocation sources at different depths using the PSGRN code. Then, we use the result as a database for PSCMP, which discretizes the earthquake's extended rupture area into several discrete point dislocations and calculates the co- and post-seismic deformation by linear superposition. For the viscoelastic mechanism modeling, it is important to consider a proper layering and velocity structure of the earth. We use the velocity structure of the GOSH seismic station implemented by the Institute for Advanced Studies in Basic Sciences to define Green’s functions. Finally, we use the distributed fault slip resulting from coseismic linear modeling as a source for viscoelastic relaxation and modeled the surface displacement for different periods after the earthquake. In the next step, we will compare the observed postseismic deformation using InSAR analysis and modeled displacement to examine whether the viscoelastic rules the postseismic movement. ‌Besides, exploring other mechanisms like afterslip and poroelastic rebound is required to fully assess the possible mechanisms.

During the RESOLVE project ("High-resolution imaging in subsurface geophysics: development of a multi-instrument platform for interdisciplinary research"), continuous surface displacement and seismic array observations were obtained on Glacier d'Argentière in the French Alps for 35 days during May in 2018. This unique data set offers the chance to perform a detailed, local study of targeted processes within the highly dynamic cryospheric environment. In particular, the physical processes controlling glacial basal motion are poorly understood and remain challenging to observe directly. Especially in the Alpine region for temperate based glaciers where the ice rapidly responds to changing climatic conditions and thus, processes are strongly intermittent in time and heterogeneous in space. Spatially dense seismic and GPS measurements are analyzed with machine learning techniques to gain insight into the underlying processes controlling glacial motions of Glacier d'Argentière.Using multiple bandpass-filtered copies of the continuous seismic waveforms, we compute energy-based features, develop a matched field beamforming catalogue and include meteorological observations.Features describing the data are analyzed with a gradient boosting decision tree model to directly estimate the GPS displacements from the seismic records.We posit that features of the seismic noise provide direct access to the dominant parameters that drive displacement on the highly variable and unsteady surface of the glacier. The machine learning model infers daily fluctuations as well as longer term trends and the results show on-ice displacement rates are strongly modulated by activity at the base of the glacier. The techniques presented provide a new approach to study glacial basal sliding and discover its full complexity.

The moderate magnitude (Mw 5.8) Ganaveh earthquake, as a compressive event. occurred on 2021 April 18 in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran. We process Sentinel-1 SAR images in ascending and descending geometries to investigate the coseismic deformation and its source parameters. The resultant displacement maps indicate a maximum of 17 cm of surface displacement in the satellite line of sight direction with no evidence of surface rupture. The NW-oriented elliptical fringes in coseismic ascending and descending displacement maps are in agreement with the strike of the major Zagros structures. The InSAR displacement map is inverted to evaluate the earthquake source parameters and the inversion results reveal a low-angle NE-dipping fault plane characterized by a maximum dip slip of 95 cm at ~6 km depth and a slight sinistral slip component (2.9 cm). Inversion of 39 earthquake focal mechanism (from 1968 to 2021), including the Ganaveh mainshock and its five larger aftershocks indicate a regional compressional stress regime and applying this stress on the retrieved Ganaveh fault plane leads to a minor sinistral movement confirming the geodetic results. InSAR coseismic displacement and relocated mainshock and aftershocks situate on the hanging wall of the Zagros Foredeep fault. This underlines the ZFF as the causative fault of the Ganaveh earthquake. The occurrence of Ganaveh moderate magnitude earthquake on the Zagros Foredeep fault highlights its role as the western structural boundary for recurrent Mb>5 events in the Dezful embayment.To examine the possibility of postseismic deformation after such a moderate magnitude earthquake in Zagros, we processed and created the interferograms using the Sentinel-1 SAR images based on the SBAS timeseries analysis approach after the mainshock until the end of 2021. The time series analysis of the constructed interferograms indicates a maximum of 7 cm of postseismic deformation with a similar strike and shape as the coseismic displacement. The short-term postseismic displacement of the Ganaveh earthquake is released seismically by aftershocks. The agreement between the cumulative displacement, cumulative number of aftershocks, and their related moment release through time and the similar pattern and direction of postseismic and coseismic deformation suggest that an afterslip mechanism can be the causative mechanism of the Ganaveh postseismic motion. We estimate a maximum of 30 cm slip at a depth of ~5 km along the coseismic causative fault plane by inverting the postseismic cumulative deformation map.

Mass balance observations are very useful to assess climate change in different regions of the world. As opposed to glacier-wide mass balances, which are influenced by the dynamic response of each glacier, point mass-balances provide a direct climatic signal that depends on surface accumulation and ablation only. Unfortunately, major efforts are required to conduct in situ measurements on glaciers. Here, we propose a new approach that determines point surface mass balances from remote sensing observations. We call this balance the geodetic point surface mass balance. From observations and modelling performed on Argentière and Mer de Glace glaciers over the last decade, we show that the vertical ice flow velocity changes are small in areas of low bedrock slope. Therefore, assuming constant vertical velocities in time for such areas and provided that the vertical velocities have been measured for at least one year in the past, our method can be used to reconstruct annual point surface mass balances from surface elevations and horizontal velocities alone. We demonstrate that the annual point surface mass balances can be reconstructed with an accuracy of about 0.3 m w.e. a-1 using the vertical velocities observed over the previous years and data from Unmanned Aerial Vehicle images. Given the recent improvements of satellite sensors, it should be possible to apply this method to high spatial resolution satellite images as well.

The Western Alps current tectonics is characterized by seismically active radial extension in the core of the belt, combined with transcurrent to transpressive tectonics in its external zone and foreland associated with a moderate seismicity. We focus on the tectonic transfer from the W-Alps to their foreland, namely the French Rhône Valley, a region with high societal challenges, including demography, nuclear powerplants, and chemical industries. We combine seismotectonic and geodetic (GNSS) approaches to constrain the stress and strain fields of the area extended from the alpine External Crystalline Massifs to the eastern edge of the French Massif Central, which encompasses the Rhône Valley. Seismic strain rates for a set of subareas defined on tectonic arguments (seismotectonic zoning) have been evaluated. They are processed by combining the total seismic energy obtained with statistical integrations of Gutenberg-Richter distributions with representative focal-mechanisms obtained from stress inversions. Seismic strain rates are then compared to the geodetic strain field obtained from an updated GNSS solution focused on the study area. Seismic strain rates of subareas in the Rhone Valley and surroundings range between a few nanostrains/yr and 10E-2 nanostrains/yr. In terms of amplitude, geodesy seems to provide deformation rates one order of magnitude higher than seismicity. However, our seismic strain tensors are globally consistent with the geodetic ones, specifically in the front of the Alps (Belledonne region), where seismic and geodetic networks are denser. In a last step, we replace these strain and stress fields in a new 3D-structural model, which has been developed on purpose. It integrates the main crustal units and the main faults of the area, allowing to better constrain the relationship between the current deformation and stress patterns of the Rhône Valley under the Alpine influence, and the inherited fault system carving the entire domain.

Recent work in the field of cryo-seismology demonstrates that high-frequency (>1 Hz) seismic waves provide key constraints on a wide range of glacier processes, such as basal friction, surface crevassing, or subglacial water flow. Establishing quantitative links between the seismic signal and the processes of interest, however, requires detailed characterization of the wavefield, which, at high frequencies, necessitates the deployment of large and dense seismic arrays. Although dense seismic array monitoring has recently become increasingly common in geophysics, its application to glaciated environments remains limited. Here, we present a dense seismic array experiment made of 98 three-component seismic stations continuously recording during 35 days in early spring 2018 on the Argentière Glacier, French Alps. The seismic dataset is supplemented with a wide range of complementary observations obtained from ground-penetrating radar, drone imagery, Global Navigation Satellite Systems positioning, and in situ measurements of basal glacier sliding velocities and subglacial water discharge. We present first results through conducting spectral analysis, template matching, matched-field processing, and eikonal-wave tomography. We report enhanced spatial resolution on basal stick slip and englacial fracturing sources as well as novel constraints on the heterogeneous nature of the noise field generated by subglacial water flow and on the link between crevasse properties and englacial seismic velocities. We outline in which ways further work using this dataset could help tackle key remaining questions in the field.

International audience; In this article, we present a method for combiningimage-based displacements to build time series. This method takesadvantage of the redundancy of these displacements, which comesfrom multiple possible combinations between images. The proposedmethod combines common master series with a differentmaster date to construct a single time series of relative displacements.We were able to test thismethod on displacements computedusing images from a stereo time-lapse device recording imagesof the Argentière glacier during the summer and fall of 2019.Our method was compared to two other displacement aggregationstrategies: a simple common master approach and the classicalinversion method. In order to perform this comparison, displacementdata from four permanent GPS are used. The results showthat our method provides a more accurate time series of relativedisplacements than those obtained with the other methods. Thehigher accuracy of the proposed method makes the detection ofseasonal variations in glacier velocity possible.

SUMMARYDue to the steady moderate seismicity observed along the Briançon seismic arc, in the south-western French Alps, three temporary GNSS (Global Navigation Satellite System) surveys took place in 1996, 2006 and 2011, across a ∼50 × 60 km² wide area, to investigate the surface deformation field. The horizontal velocity field computed from these three surveys showed an east–west extension in the network. A fourth campaign was led in 2016, creating a 20 yr observation span, resulting in measurements which reach a sufficient accuracy to assess whether extension found within the Briançon network is localized onto any particular tectonic feature. Several faults in this area are known to be active normal faults. Assessing the localization of the deformation may lead to a better understanding of the active tectonics of the Alpine belt. To address this issue, a robust velocity field was computed from the combination of the different campaign and permanent GNSS data. Strain rate tensors were derived for the first time in this area on a 0.1 × 0.1 deg grid to assess the distribution of the deformation. The regional deformation appears localized in the Briançon area and reaches up to 20 ± 5 nanostrain yr−1 in the centre of the network. The observed velocities were projected on a profile across the network and compared with modelled interseismic deformation to characterize the behaviour of the major active faults known in the study zone. While a two-fault model provides the best fit to the data, a single fault model has only marginally higher residuals, with parameters which are more consistent with the seismotectonics of the region. The localization of the single modelled fault is consistent with the location of the High Durance Fault (HDF). Therefore, we used the known geological location of this structure as a priori information in a block model to compute a fault slip rate at the interface between the two blocks. The velocities on the interface indicate 0.4–0.5 mm yr−1 of extension, and therefore strain accumulates along the HDF throughout the seismic cycle. The geodetically derived fault slip rate is converted into an equivalent seismic moment release rate, which is consistent within its uncertainty bounds with the known historical and instrumental seismicity of the Briançon area.

In the last decades, GNSS constraints and geological estimates of the fault slip rates improve the understating of the kinematics of faulting across Iran, particularly in the northeastern part of the country. Here, we complete the sparse GNSS vectors from previous reported studies around the Baghan Quchan fault zone (BQFZ) in northeastern Iran, by processing the Sentinel-1 archives covering this zone. According to tectonic and geodetic studies, the right-lateral BQFZ and the left-lateral Esfarayen fault constitute the northeastern and southern limits, respectively, of the easternmost part of the South Caspian Basin. While the BQFZ is limiting the SCB towards Eurasia, the Esfarayen fault is its border towards the Iranian microplate. We constructed 452 interferograms with 102 images from 2014.10.29 to 2019.10.27 (5 years) in descending geometry using the NSBAS package. We combined all three swaths (iw1, iw2, iw3) to cover the area of interest. The revisit time is 24 days between 2014.10.29 and 2017.02. 15, and 12 days from 2017.02.15 to 2019.10.27. To remove the hydrogeological land displacement effect (charge and discharge of aquifers), we chose the first (2014.10.29) and the last image (2019.10.27) at the same time of the year. Following the SBAS time series analysis approach, we created interferograms with short temporal (one or two months) and spatial baselines. Also, to avoid introducing any artificial signal in the mean velocity map, we created some interferograms with longer temporal baselines (maximum one year). We removed the neutral atmospheric delay using global reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Then, we filtered and unwrapped the generated interferograms. We applied the SBAS time series analysis on the generated interferograms to obtain displacement variations in time and a mean velocity map in the line of sight (LOS) direction of the satellites. The first noticeable point is the LOS mean velocity change across the BQFZ fault reaching up to ~1.5 mm/yr in the LOS direction, compatible with right-lateral displacement. Moreover, the mean velocity map varies significantly across the Esfarayen fault, in a sense coherent with left-lateral displacement. This velocity map points out that the NW motion of the South Caspian basin is effectively accommodated by the Esfarayen fault, while previous work based on the sparse GNSS network (Mousavi et al., 2013) suggested that the Bojnord fault further north is accommodating this NW motion. In particular, the new InSAR map indicates that the velocity vector of the permanent GNSS station ESFN used by Mousavi et al. (2013) is contaminated by subsidence motion and cannot be representative of a tectonic motion. This study brings new information for assessing seismic hazard in NE Iran with large population centers. Moreover, the retrieved mean velocity map indicates significant subsidence in Nishabour and Jajarm cities and Joveyn, Chahar Borj, Chenaran, Faruj and Ribat Jaz villages in Iran, as well as in the Yashklik city in Turkmenistan. This is the first report of subsidence occurring in Turkmenistan.