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In this article, we analyze the rotation rates in a building derived from a network of translation sensors and recorded by a rotation sensor. The building is Grenoble city hall, a reinforced concrete structure with permanent accelerometric translation sensors at the top and bottom of the building. A temporary experiment was conducted, consisting in installing a BlueSeis-3A rotation sensor for more than 24 h at the top of the structure. The ambient vibrations were analyzed. The amplitudes of translation accelerations and rotation rates at the top and bottom of the building, along with their variations over time, were analyzed. The acceleration/rotation ratios were then compared with the impulse wave velocities derived from seismic interferometry by deconvolution between the top and bottom. Perspectives with regard to building imaging, time monitoring of structural integrity and understanding the contribution of rotations to the structure’s response are discussed, offering new suggestions for research projects.

We utilize train tremors as P‐wave seismic sources to investigate velocity‐strain sensitivity near the San Jacinto Fault Zone. A dense nodal array deployed at the Piñon Flat Observatory is used to detect and identify repeating train energy emitted from a railway in the Coachella valley. We construct P‐wave correlation functions across the fault zone and estimate the spatially averaged dt/t versus strain sensitivity to be 6.25 × 104. Through numerical simulations, we explore how the sensitivity decays exponentially with depth. The optimal solution reveals a subsurface sensitivity of 1.2 × 105 and a depth decay rate of 0.05 km−1. This sensitivity aligns with previous findings but is toward the higher end, likely due to the fractured fault‐zone rocks. The depth decay rate, previously unreported, is notably smaller than assumed in empirical models. This raises the necessity of further investigations of this parameter, which is crucial to study stress and velocity variations at seismogenic depth. Plain Language Summary The speed at which seismic waves travel can be affected by Earth's tidal strains. Understanding this relationship is beneficial for studying tectonic strain accumulation and earthquake nucleation. When freight trains run, they produce powerful seismic energy that can be detected tens of kilometers away. We use these signals to measure how solid Earth tides affect seismic wave speed. Our study focusing on the San Jacinto Fault Zone in southern California reveals that the velocity‐strain sensitivity is consistent, albeit at the higher end of previously reported values measured in other regions. Additionally, our numerical simulations examine how this sensitivity varies with depth. We find that the rate at which sensitivity decreases with depth is smaller than what is typically assumed. Key Points Stable P‐wave correlation functions are constructed from selected train tremors The covariance between tidal strain and P‐wave travel‐time is used to estimate the velocity‐strain sensitivity Full‐waveform simulations of correlation functions are performed to constrain the depth dependence of the velocity‐strain sensitivity

Abstract We utilize train tremors as P‐wave seismic sources to investigate velocity‐strain sensitivity near the San Jacinto Fault Zone. A dense nodal array deployed at the Piñon Flat Observatory is used to detect and identify repeating train energy emitted from a railway in the Coachella valley. We construct P‐wave correlation functions across the fault zone and estimate the spatially averageddt/tversus strain sensitivity to be 6.25 × 104. Through numerical simulations, we explore how the sensitivity decays exponentially with depth. The optimal solution reveals a subsurface sensitivity of 1.2 × 105and a depth decay rate of 0.05 km−1. This sensitivity aligns with previous findings but is toward the higher end, likely due to the fractured fault‐zone rocks. The depth decay rate, previously unreported, is notably smaller than assumed in empirical models. This raises the necessity of further investigations of this parameter, which is crucial to study stress and velocity variations at seismogenic depth.

The recent installation of new broadband seismic stations in the French Massif Central (FMC) has resulted in the detection of a few “deep” earthquakes located near the crust‐mantle boundary beneath volcanic regions. Analysis of the spectral content of the respective waveforms has shown that the spectra of these “deep” earthquakes are significantly depleted in high frequencies. Based on these observations of anomalous depth and spectral content, these earthquakes can be classified as Deep Long Period (DLP) events. This is a specific class of volcanic seismicity observed beneath many active volcanoes around the World. While the exact physical origin of this type of earthquakes is still debated, they are often considered as indicators of the presence of magma near the crust‐mantle boundary. Therefore, observation of DLP earthquakes can bring new insights into understanding the state and the activity of the recent FMC volcanoes.

The recent installation of new broadband seismic stations in the French Massif Central (FMC) has resulted in the detection of a few “deep” earthquakes located near the crust‐mantle boundary beneath volcanic regions. Analysis of the spectral content of the respective waveforms has shown that the spectra of these “deep” earthquakes are significantly depleted in high frequencies. Based on these observations of anomalous depth and spectral content, these earthquakes can be classified as Deep Long Period (DLP) events. This is a specific class of volcanic seismicity observed beneath many active volcanoes around the World. While the exact physical origin of this type of earthquakes is still debated, they are often considered as indicators of the presence of magma near the crust‐mantle boundary. Therefore, observation of DLP earthquakes can bring new insights into understanding the state and the activity of the recent FMC volcanoes.

The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps–Apennines–Carpathians–Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth.

Fluids in subduction zones can have major effects on subduction dynamics. However, geophysical constraints on the scale and impact of fluid flow during continental subduction are still limited. Here we analyze the V P / V S ratios in the Western Alpine region, hosting one of the best-preserved fossil continental subduction zones worldwide, to investigate the impact of fluid flow during continental subduction. We found a belt of high V P / V S ratios >1.9 on the upper-plate side of the subduction zone, consistent with a partially serpentinized upper-plate mantle, and a belt of unusually low V P / V S ratios <1.7 on the lower-plate side, at depths shallower than 30 km. We propose that these low V P / V S ratios result from a widespread network of silica-rich veins, indicating past fluid flow along the continental subduction interface. Our results suggest that past fluid flow may have reduced the effective stress along the subduction interface thus favoring continental subduction.

There are still open questions about the deep structure beneath the Western Alps. Seismic velocity tomographies show the European slab subducting beneath the Adria plate, but all these images did not clarify completely the possible presence of tears, slab windows, or detachments. Seismic anisotropy, considered as an indicator of mantle deformation and studied using data recorded by dense networks, allows a better understanding of mantle flows in terms of location and orientation at depth. Using the large amount of shear wave splitting and splitting intensity measurements available in the Western Alps, collected through the CIFALPS2 temporary seismic network, together with already available data, some new patterns can be highlighted and gaps left by previous studies can be filled. Instead of the typical seismic anisotropy pattern parallel to the entire arc of the Western Alps, this study supports the presence of a differential contribution along the belt, only partly related to the European slab steepening. A nearly NS anisotropy pattern beneath the external Western Alps, a direction that cuts the morphological features of the belt, is clearly found with the new CIFALPS2 measurements. It is however confirmed that the asthenospheric flow from Central France towards the Tyrrhenian Sea, is turning around the southern tip of the European slab.

There are still open questions about the deep structure beneath the Western Alps. Seismic velocity tomographies show the European slab subducting beneath the Adria plate, but all these images did not clarify completely the possible presence of tears, slab windows, or detachments. Seismic anisotropy, considered an indicator of mantle deformation and studied using data recorded by dense networks, allows a better understanding of mantle flows in terms of location and orientation at depth. Using the large amount of shear wave-splitting and splitting-intensity measurements available in the Western Alps, collected through the CIFALPS2 temporary seismic network, together with already available data, some new patterns can be highlighted, and gaps left by previous studies can be filled. Instead of the typical seismic anisotropy pattern parallel to the entire arc of the Western Alps, this study supports the presence of a differential contribution along the belt that is only partly related to the European slab steepening. A nearly north–south anisotropy pattern beneath the external Western Alps, a direction that cuts the morphological features of the belt, is clearly found with the new CIFALPS2 measurements. It is, however, confirmed that the asthenospheric flow from central France towards the Tyrrhenian Sea is turning around the southern tip of the European slab.

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.