Locating the Nordstream explosions without a velocity model using polarization analysis

The seismic events that preceded the leaks in the Nordstream pipelines in the Baltic Sea have been interpreted as explosions on the seabed, most likely man-made. We use a polarization-based location method initially developed for marsquakes to locate the source region without a subsurface velocity model. We show that the 2 largest seismic events can be unambiguously attributed to the methane plumes observed on the sea surface. The two largest events can be located with this method, using 4 and 5 stations located around the source, with location uncertainties of 30km and 10x60km. We can further show that both events emitted seismic energy for at least ten minutes after the initial explosion, indicative of resonances in the water column or the depressurizing pipeline.Comment: 6 pages, 2 figures, submitted as fast report to Seismic

Seismic detection of the martian core by InSight

A plethora of geophysical, geo- chemical, and geodynamical observations indicate that the terrestrial planets have differentiated into silicate crusts and mantles that surround a dense core. The latter consists primarily of Fe and some lighter alloying elements (e.g., S, Si, C, O, and H) [1]¿. The Martian meteorites show evidence of chalcophile element depletion, suggesting that the otherwise Fe-Ni- rich core likely contains a sulfide component, which influences physical state

Largest recent impact craters on Mars: Orbital imaging and surface seismic co-investigation.

Two >130-meter-diameter impact craters formed on Mars during the later half of 2021. These are the two largest fresh impact craters discovered by the Mars Reconnaissance Orbiter since operations started 16 years ago. The impacts created two of the largest seismic events (magnitudes greater than 4) recorded by InSight during its 3-year mission. The combination of orbital imagery and seismic ground motion enables the investigation of subsurface and atmospheric energy partitioning of the impact process on a planet with a thin atmosphere and the first direct test of martian deep-interior seismic models with known event distances. The impact at 35°N excavated blocks of water ice, which is the lowest latitude at which ice has been directly observed on Mars

Resonances and Lander Modes Observed by InSight on Mars (1–9 Hz)

The National Aeronautics and Space Administration’s (NASAs) Interior exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander successfully touched down on Mars in November 2018, and, for the first time, a seismometer was deployed on the surface of the planet. The seismic recordings reveal diurnal and seasonal changes of the broadband noise level that are consistent with variations of the local atmospheric conditions. The seismic data include a variety of spectral peaks, which are interpreted as wind-excited,mechanical resonances of the lander, resonances of the subsurface, or artifacts produced in themeasurement system. Understanding the origin of these signals is critical for the detection and characterization of marsquakes as well as for studies investigating the ambient noise. We identify the major spectral peaks up to 9 Hz, corresponding to the frequency range the most relevant to observed marsquakes. We track the variations in frequency, amplitude, and polarization of these peaks over the duration of the mission so far. The majority of these peaks can readily be classified as measurement artifacts or lander resonances (lander modes), of which the latter have a temperature-dependent peak frequency and a wind-sensitive amplitude. Of particular interest is a prominent resonance at 2.4 Hz, which is used to discriminate between seismic events and local noise and is possibly produced by a subsurface structure. In contrast to the lander modes, the 2.4 Hz resonance has distinctly different features: (1) a broad and stable spectral shape, slightly shifted on each component; (2) predominantly vertical energy; (3) temperature-independent peak frequency; (4) comparatively weak amplification by local winds, though there is a slow change in the diurnal and seasonal amplitude; and (5) excitation during all seismic events that excite this frequency band. Based on these observations, we suggest that the 2.4 Hz resonance is the only mode below 9 Hz that could be related to a local ground structureThe authors acknowledge National Aeronautics and Space Administration (NASA), The National Centre for Space Studies of France (CNES), their partner agencies and institutions (UK Space Agency [UKSA], Swiss Space Office [SSO], Deutsches Zentrum für Luft- und Raumfahrt [DLR], Jet Propulsion Laboratory [JPL], Institut du Physique du Globe de Paris Centre National de la Recherche Scientifique [IPGP-CNRS], Eidgenössische Technische Hochschule Zürich [ETHZ], Imperial College London [IC], Max-Planck Institut for Solar System Research [MPS-MPG]), and the flight operations team at JPL, SEIS on Mars Operation Center (SISMOC), Mars SEIS Package Data Service (MSDS), Incorporated Research Institutions for Seismology Data Management Center (IRIS-DMC), and Planetary Data System (PDS) for providing Standard for the Exchange of Earthquake Data (SEED) Seismic Experiment for Interior Structure (SEIS) data. We acknowledge funding from (1) Swiss State Secretariat for Education, Research, and Innovation (SEFRI project “MarsQuake Service-Preparatory Phase”), (2) ETH Research grant ETH-06 17-02, and (3) ETH+02 19-1: Planet MARS. The Swiss contribution in implementation of the SEIS electronics was made possible through funding from the federal Swiss Space Office (SSO), the contractual and technical support of the European Space Agency – Programme de Développement d'Expériences scientifiques (ESA-PRODEX) office. The French authors acknowledge the French Space Agency CNES and French National Agency for Research (ANR) (ANR-14-CE36-0012-02 and ANR‐19-CE31-0008-08) for support in the Science analysis. This is Interior exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) contribution 202.Peer reviewe

Origin of turbidites in deep lake Geneva (France-Switzerland) in the last 1500 years

Turbidites in lacustrine sediments are commonly used to assess the frequencies of flood events and/or earthquakes. Understanding the origin of those deposits is key to adequately assess the sources and triggers of such events in large lacustrine systems. Ca/Ti X-ray fluorescence core scanner and magnetic susceptibility values on sediment cores of the deep basin of Lake Geneva are used as a provenance indicator of the turbidites either from the Dranse or Rhone deltas or from the slopes not influenced by deltaic input. This tool is validated by mineralogical analyses (X-ray diffraction), major-, and trace-element geochemistry (X-ray fluorescence). Based on this discrimination method, the turbidites deposited in the central part of the deep basin can be classified regarding their origin. From all identified turbidites, four turbidites are chosen based on their large depositional area and volumes and are studied in more detail in order to better understand the processes leading to turbidite deposition in the deep basin. The age intervals of these turbidites were compared to the historical records of extreme events in the region of Lake Geneva. These turbidites can be related to extreme floods, earthquakes, and >spontaneous> delta collapses. The cause of two turbidites could not be identified precisely due to large dating intervals that did not allow attributing a specific historical event to the turbidite layer. Overall, this study provides a tool in classifying the turbidites in deep Lake Geneva and exemplifies that defining the cause of turbidites is complex although it remains a prerequisite for paleohydrology and paleoseismology studies.Peer Reviewe

Mapping the Seismicity of Mars With InSight

International audienceThe InSight seismometers have recorded more than 1,300 events. Ninety-eight of these, named the low-frequency (LF) family, show energy predominantly below 1 Hz down to ∼0.1 Hz. The Marsquake Service identified seismic phases and computed distances for 42 of these marsquakes, 24 of which have backazimuths. Hence, the locations of the majority of LF family events remain undetermined. Here, we use an envelope shape similarity approach to determine event classes and distances, and introduce an alternative method to estimate the backazimuth. In our analysis, we use the highest quality marsquakes with known distances as templates, including the largest event S1222a, and assign new distances to similar group of events for which distance estimates were not previously available. We find the Tharsis region to be more active than initially perceived on the basis of 5 newly located events near Valles Marineris and Olympus Mons. We relocate two marsquakes with little or no S-wave energy in the NE of the Elysium Bulge. The event epicenters in Cerberus Fossae follow a north-south trend due to uncertainties in location, while the fault system is in the NW-SE direction; therefore, these events are re-projected along the observed fault system based on our interpretations. The marsquakes in our interpreted catalog are predominantly observed in the northern hemisphere of Mars above the equatorial dichotomy boundary

Identifying and interpreting regional signals in tree-ring based reconstructions of snow avalanche activity in the Goms valley (Swiss Alps)

International audienceOne of the purposes of dendrogeomorphic studies is to provide long and continuous reconstructions of mass movements and to detect climate-induced trends in process activity. The development of regional chronologiesdin which information from different sites are aggregateddis often needed to identify processeclimate relations and to overcome local-scale specificities, sparse data available for individual sites and to extract a signal that is common to a larger region and possibly driven by past climate fluctuations or large-scale environmental changes. Yet, such chronologies are scarce and consensus neither exists on how to compile local data at the regional scale nor on the methods to be used to extract a common signal. In the case of snow avalanches, existing regional tree-ring studies typically included less than ten paths, and they discriminated years of high/low avalanche activity based on a regional index representing the proportion of disturbed trees in any given year. However, such an index does not account for potential non-stationarities in local tree-ring reconstructions such as e.g., time-varying sample size, decreasing dendrogeomorphic potential of trees after the occurrence of an extremely large, devastating avalanche or socio-environmental changes. Here we combine a dendrogeomorphic approach to reconstruct snow avalanche events in 11 paths located in the Goms valley (Swiss Alps) with an innovative statistical modelling approach. For each path, we compute reconstructions using a 4-step procedure to disentangle potential effects of snow avalanches from disturbance pulses in trees caused by climatic or other exogenous factors. We then process the regional dataset (spanning the period 1766-2014) within a Bayesian hierarchical spatio-temporal framework specifically designed to homogenise time series of avalanche events by i) removing trends related to the decreasing number of living trees back in time and ii) inferring robust trends in mean annual/regional avalanche activity in time and space. This contribution has the merit to introduce a methodological approach allowing rigorous extraction of common, average avalanche signals from snow avalanche paths characterized by heterogeneous process activity. Despite its stringency, we show that 11 avalanche paths may not suffice to yield a signal that is independent from the selection of couloirs. As a result, the approach also does not highlight a clear climatic control of snow avalanche activity but rather points to a complex, yet combined impact of afforestation and management strategies on reconstructed avalanches