Explore the vast range of titles available.

We launched an array of nine freely floating submarine seismometers near the Galápagos islands, which remained operational for about two years. P and PKP waves from regional and teleseismic earthquakes were observed for a range of magnitudes. The signal-to-noise ratio is strongly influenced by the weather conditions and this determines the lowest magnitudes that can be observed. Waves from deep earthquakes are easier to pick, but the S/N ratio can be enhanced through filtering and the data cover earthquakes from all depths. We measured 580 arrival times for different raypaths. We show that even such a limited number of data gives a significant increase in resolution for the oceanic upper mantle. This is the first time an array of floating seismometers is used in seismic tomography to improve the resolution significantly where otherwise no seismic information is available. We show that the Galápagos Archipelago is underlain by a deep (about 1900 km) 200–300 km wide plume of high temperature, with a heat flux very much larger than predicted from its swell bathymetry. The decrease of the plume temperature anomaly towards the surface indicates that the Earth’s mantle has a subadiabatic temperature gradient.

Our understanding of the internal dynamics of the Earth is largely based on images of seismic velocity variations in the mantle obtained with global tomography. However, our ability to image the mantle is severely hampered by a lack of seismic data collected in marine areas. Here we report observations made under different noise conditions (in the Mediterranean Sea, the Indian and Pacific Oceans) by a submarine floating seismograph, and show that such floats are able to fill the oceanic data gap. Depending on the ambient noise level, the floats can record between 35 and 63% of distant earthquakes with a moment magnitude M ≥6.5. Even magnitudes <6.0 can be successfully observed under favourable noise conditions. The serendipitous recording of an earthquake swarm near the Indian Ocean triple junction enabled us to establish a threshold magnitude between 2.7 and 3.4 for local earthquakes in the noisiest of the three environments. Our understanding of the internal dynamics of the Earth is limited by the lack of seismic data available from oceanic domains. Here, the authors use observations from floating submarine seismographs to show that this technique may provide seismic data to fill the gaps in our knowledge.

A broadband seismological station (PRIMA) installed offshore Nice airport (southeastern France) reveals a strong amplification effect of seismic waves. PRIMA station was in operation for 2 years (9/2016 to 10/2018) on the outer shelf at a water depth of 18 m. Situated at the mouth of the Var River, this zone is unstable and prone to landslides. A catastrophic landslide and tsunami already occurred in 1979, causing 10 casualties. Given the level of seismicity of the area, it is important to infer the impact of an earthquake on this zone. We analyze the recordings of earthquakes and seismic noise at the PRIMA station by comparing them to nearby inland stations. We find that the seismic waves are strongly amplified at PRIMA at some specific frequencies (with an amplification factor greater than 10 at 0.9 Hz). Using geological and geophysical data, we show that the main amplification frequency peak (at 0.9 Hz) is due to the velocity contrast between the Pliocene sedimentary layer and fine-grained sediments dated from the Holocene, at about 100 m depth. This velocity contrast is also present along the Var valley, but the level of amplification detected on PRIMA station is larger. Using numerical simulations of seismic waves in a 2D model that accounts for the pinch-out geometry related to the termination of the Holocene sedimentary layer, we can partially explain this amplification. This offshore site effect could have a crucial impact on the triggering of a submarine landslide by an earthquake in this region. More generally, this effect should be taken into account for the modeling of landslides and induced tsunamis triggered by seismic waves.

At 2000 m depth in the oceans, one can hear biological, seismological, meteorological, and anthropogenic activity. Acoustic monitoring of the oceans at a global scale and over long periods of time could bring important information for various sciences. The Argo project monitors the physical properties of the oceans with autonomous floats, some of which are also equipped with a hydrophone. These have a limited transmission bandwidth requiring acoustic data to be processed on board. However, developing signal processing algorithms for these instruments requires one to be an expert in embedded software. To reduce the need of such expertise, we have developed a programming language, called MeLa. The language hides several aspects of embedded software with specialized programming concepts. It uses models to compute energy consumption, processor usage, and data transmission costs early during the development of applications; this helps to choose a strategy of data processing that has a minimum impact on performances. Simulations on a computer allow for verifying the performance of the algorithms before their deployment on the instrument. We have implemented a seismic P wave detection and a blue whales D call detection algorithm with the MeLa language to show its capabilities. These are the first efforts toward multidisciplinary monitoring of the oceans, which can extend beyond acoustic applications.

The European Space Agency's (ESA) Aeolus satellite mission is the first Doppler wind lidar in space, operating in orbit for more than 4 years since August 2018 and providing global wind profiling throughout the entire troposphere and the lower stratosphere. The Observatoire de Haute-Provence (OHP) in southern France and the Observatoire de Physique de l'Atmosphère de La Réunion (OPAR) are equipped with ground-based Doppler Rayleigh–Mie lidars, which operate on similar principles to the Aeolus lidar and are among essential instruments within the ESA Aeolus calibration and validation (cal/val) program. This study presents the validation results of the L2B Rayleigh clear horizontal line-of-sight (HLOS) winds from September 2018 to January 2022. The point-by-point validation exercise relies on a series of validation campaigns at both observatories: AboVE (Aeolus Validation Experiment), held in September 2019 and June 2021 at OPAR and in January 2019 and December 2021 at OHP. The campaigns involved time-coordinated lidar acquisitions and radiosonde ascents collocated with the nearest Aeolus overpasses. During AboVE-2, Aeolus was operated in a campaign mode with an extended range bin setting allowing inter-comparisons up to 28.7 km. We show that this setting suffers from larger random error in the uppermost bins, exceeding the estimated error, due to lack of backscatter at high altitudes. To evaluate the long-term evolution in Aeolus wind product quality, twice-daily routine Météo-France radiosondes and regular lidar observations were used at both sites. This study evaluates the long-term evolution of the satellite performance along with punctual collocation analyses. On average, we find a systematic error (bias) of −0.92 and −0.79 m s−1 and a random error (scaled MAD) of 6.49 and 5.37 m s−1 for lidar and radiosondes, respectively.

Active galaxies, especially blazars, are among the most promising extragalactic candidates for high-energy neutrino sources. To date, ANTARES searches included these objects and used GeV–TeV γ-ray flux to select blazars. Here, a statistically complete blazar sample selected by their bright radio emission is used as the target for searches of origins of neutrinos collected by the ANTARES neutrino telescope over 13 yr of operation. The hypothesis of a neutrino–blazar directional correlation is tested by pair counting and a complementary likelihood-based approach. The resulting posttrial p-value is 3.0% (2.2σ in the two-sided convention). Additionally, a time-dependent analysis is performed to search for temporal clustering of neutrino candidates as a means of detecting neutrino flares in blazars. None of the investigated sources alone reaches a significant flare detection level. However, the presence of 18 sources with a pretrial significance above 3σ indicates a p = 1.4% (2.5σ in the two-sided convention) detection of a time-variable neutrino flux. An a posteriori investigation reveals an intriguing temporal coincidence of neutrino, radio, and γ-ray flares of the J0242+1101 blazar at a p = 0.5% (2.9σ in the two-sided convention) level. Altogether, the results presented here suggest a possible connection of neutrino candidates detected by the ANTARES telescope with radio-bright blazars.

In the quest for high-energy neutrino sources, the Astrophysical Multimessenger Observatory Network has implemented a new search by combining data from the High Altitude Water Cherenkov (HAWC) Observatory and the Astronomy with a Neutrino Telescope and Abyss environmental RESearch (ANTARES) neutrino telescope. Using the same analysis strategy as in a previous detector combination of HAWC and IceCube data, we perform a search for coincidences in HAWC and ANTARES events that are below the threshold for sending public alerts in each individual detector. Data were collected between 2015 July and 2020 February with a live time of 4.39 yr. Over this time period, three coincident events with an estimated false-alarm rate of <1 coincidence per year were found. This number is consistent with background expectations.

After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N‐S compressive mechanism, and not the expected left‐lateral strike‐slip mechanism. A first‐order slip model of the mainshock shows a N264°E north‐dipping plane, with a major left‐lateral component and a strong reverse component. As the aftershock distribution is sub‐parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north‐dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south‐dipping faults, such the Trois‐Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt: the rupture occurred on a wrench fault at the rheologic boundary on top of the under‐thrusting rigid oceanic block, whereas the aftershocks were the result of the relaxation on the hanging wall along pre‐existing discontinuities in the frontal part of the Transhaitian Belt. Key Points Active fault identification for the Jan.12, 2010 Haiti earthquake Ocean Bottom Seismometer ued for aftershocks studies Transpressive mechanism for the Jan.12, 2010 Haiti earthquake

Position calibration in the deep sea is typically done by means of acoustic multilateration using three or more acoustic emitters installed at known positions. Rather than using hydrophones as receivers that are exposed to the ambient pressure, the sound signals can be coupled to piezo ceramics glued to the inside of existing containers for electronics or measuring instruments of a deep sea infrastructure. The ANTARES neutrino telescope operated from 2006 until 2022 in the Mediterranean Sea at a depth exceeding 2000 m . It comprised nearly 900 glass spheres with 432 mm diameter and 15 mm thickness, equipped with photomultiplier tubes to detect Cherenkov light from tracks of charged elementary particles. In an experimental setup within ANTARES, piezo sensors have been glued to the inside of such – otherwise empty – glass spheres. These sensors recorded signals from acoustic emitters with frequencies from 46545 to 60235 Hz . Two waves propagating through the glass sphere are found as a result of the excitation by the waves in the water. These can be qualitatively associated with symmetric and asymmetric Lamb-like waves of zeroth order: a fast (early) one with v e ≈ 5 mm / μ s and a slow (late) one with v ℓ ≈ 2 mm / μ s . Taking these findings into account improves the accuracy of the position calibration. The results can be transferred to the KM3NeT neutrino telescope, currently under construction at multiple sites in the Mediterranean Sea, for which the concept of piezo sensors glued to the inside of glass spheres has been adapted for monitoring the positions of the photomultiplier tubes.