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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.

The Great Rift Valley: a dividing continent Africa's Great Rift Valley is geologically active: gradually the continent is being split in two. In July and August 2007 one of the discrete rifting events contributing to this continental break-up was recorded in the form of a seismic crisis in the Lake Natron area, Tanzania. This provided an opportunity to examine the respective roles of faulting and magmatism in the rifting process. Data from the local seismic network, GPS stations and the Envisat satellite reveal that initial ground deformation was due to aseismic slip on a fault on the eastern side of the rift, and then to the emplacement of magma into the crust. This points to strain accommodation by magma intrusion as a major factor — in addition to slow slip along normal faults — during the early stages of continental rifting. Continental rifts initiate and develop through repeated episodes of faulting and magmatism, yet strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. It is shown that most of the strain during the July–August 2007 seismic crisis in the Natron rift, Tanzania, was released aseismically. This event provides evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting, and before significant crustal thinning. Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions 1 , 2 , 3 . These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July–August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning.

Long-term datasets documenting the evolution of coastal forms and processes, through the provision of recurring beach as well as shoreface morphological observations and accompanying time-series of environmental controls, remain difficult to collect and are rarely made available. However, they are increasingly needed to further our understanding of coastal change and to improve the models that will help planning what our future coast will be. This data descriptor presents the results of topographic and bathymetric surveys at Porsmilin, a macrotidal embayed beach situated in Brittany, northwest France. The Porsmilin beach survey program was launched in January 2003 by the Institut Universitaire Européen de la Mer (IUEM/Univ. Brest) and is continuing today in the framework of the French coastal observation service SNO-DYNALIT. The dataset contains over 16 years of monthly beach profile surveys and a large collection of repeated high-resolution subtidal and subaerial digital elevation models (DEMs). The dataset is accompanied by time-series of inshore waves and water levels, and enriched metadata, that will facilitate its future reuse in coastal research.Measurement(s)Beach topography • Nearshore bathymetryTechnology Type(s)RTK-GNSS • Terrestrial laser scanning • Digital photogrammetry • Multibeam echosounderFactor Type(s)ElevationSample Characteristic - EnvironmentshoreSample Characteristic - LocationBretagne Region

This report is based on the Federation of American Societies for Experimental Biology’s symposium, “Engaging basic Scientists in Translational Research: Identifying Opportunities, Overcoming Obstacles,” held in Chevy Chase, MD, March 24–25, 2011. Meeting participants examined the benefits of engaging basic scientists in translational research, the challenges to their participation in translational research, and the roles that research institutions, funding organizations, professional societies, and scientific publishers can play to address these challenges.

The point source parameters of the 11 November 2019 Le Teil earthquake (Mw 4.9) in France are revisited. Previous hypocenter determinations either located it on the wrong side of the causative fault, or had to restrain the depth ranges to obtain epicenters compatible with the fault geometry. Here, relocation is carried out with three different approaches: (1) using as a master event an aftershock well-recorded by the post-earthquake temporary seismic network; (2) optimizing the velocity model in two subareas; and (3) using a quarry blast. All three approaches concur in a common epicentral area located in the middle of the rupture, confirming its bilateral character. Hypocentral depth is best constrained at 1 . 5 ± 0 . 5 km , a range confirmed by waveform inversion. The dip of the SE-dipping nodal plane corresponding to the fault is not well constrained by waveform inversion, but the focal mechanism at rupture initiation determined with the first motions suggests that fault dip may be constant (50°–60°) from the surface down to 1–1.5 km depth. Optimized velocity models point to a strong velocity contrast, mainly in the V p / V s ratio, between the NW and the SE sides of the Cevennes fault system, which clearly correlates with the geology.

The analysis of the seismicity catalog (1996 to 2019) covering the region from the Jura mountains to Corsica provides a first-order image of the distribution of earthquakes, highlighting large structures such as the Briançonnais and Piedmontais seismic arcs, the eastward deepening of the focal depths through the Western Alps, several large active faults (e.g. Belledonne, Middle Durance, Ligure). Over this period the magnitudes are moderate and the focal mechanisms of the main events display a diversity of seismic behaviors that can be explained by the complexity of the different geological domains with a more or less strong structural inheritage, by variable rheological characteristics at the scale of the crust and by the joint action of different mechanisms of deformation. The distribution of the historical events is in fairly good agreement with the instrumental seismicity, but several earthquakes of M > 6 are highlighted since the 14th century until the beginning of the 20th.

This paper describes the application of an evolutionary optimization method to design satellite constellation for continuous regional coverage without intersatellite links. This configuration, called mutual coverage, is related to some technical limitations that exist on small satellite technology. The coverage of the north Algerian seismological network is taken as an example of application. A Multi Objective Genetic Algorithm (MOGA) is used to make a trade-off between the improvement of the coverage rate, the minimization of the total number of satellites and the reduction of the satellites’ altitude. First, some experiments have been performed to find the weight distribution of the fitness function that shows the most significant improvement of the average fitness function. Then, some optimized constellation designs are given for different ranges of altitude and it is shown that the size of the MOGA constellation design is significantly reduced compared to the traditional geometrical design.

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.

Moskalski, S.; Floc'h, F.; Verney, R.; Fromant, G.; Le Dantec, N., and Deschamps, A., 2018. Sedimentary dynamics and decadal-scale changes in the macrotidal Aulne River estuary, Brittany, France. Studies of macrotidal estuaries have been dominated by large, high-turbidity systems like the Gironde and Severn, but some macrotidal estuaries are different from these systems. The goal of this study was to document the state of hydrosedimentary processes in the macrotidal, low-turbidity Aulne River estuary and, where possible, compare it to a previous study. Study sites from a 1977 study were revisited in 2013. Observations of velocity, salinity, and suspended sediment concentration were analyzed and compared to the 1977 study, with particular attention given to hourly data. The results illustrate the impact of shallowing on hydrosedimentary processes. The estuary is strongly dominated by spring–neap variability and shallowing, with increasing tidal distortion in the landward direction and a turbidity maximum zone created by sediment resuspension. The maximum flooding and ebbing velocity were stronger and tidal velocity distortion was more pronounced than in 1977. The salinity intrusion moved farther landward during low discharge in 2013 than in 1977, but not during average and high discharge. Other hydrosedimentary processes remained consistent with the previous study. This study also illustrates potential problems that can occur when attempting to use historical analyses.

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.