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ABSTRACT Garlan, T.; Mathias, X.; Brenon E.; Favretto-Cristini, N.; Deschamps, A.; Beucler, E., Guyomard P., and Morio, O., 2018. Circular sedimentary figures of anthropic origin in a sediment stability context. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 411–415. Coconut Creek (Florida), ISSN 0749-0208. The French POSA project studies the seismic energy released by bomb and mine blasting. This project is based on seismological and acoustical measurements recording during blasting actions in order to study seismic wave propagation nucleated by controlled sources (location and explosive energy). These measurements are compared to numerical modeling of the acoustic and seismic wave propagation based on the most faithful 3D representation of the seabed sediments and underlying rocks. This project first focused on the 3D environment representation based on specific surveys and on two blasting experiments which consist in exploding bombs of different loads at two distinct environmental places. The in-situ measurements reveal several hundred circular figures with very specific characteristics which clearly differentiate them from other sedimentary, biological and geological figures encountered on the seabed. They are found within the whole studied area and their diameter is from 10 to 130 m. About 30 circles by kilometer square are observed without correlation with the depth which varies from 10 to 150m. These sedimentary structures indicate that they have been generated by the explosion of bombs, but at different periods. The oldest ones most probably result from bombs dropped in 1940 and 1944 during the landing of the Allied forces in the region of Toulon. These original anthropic sedimentary figures and their differences compared with other circular structures observed on the seabed are described. [ABSTRACT FROM AUTHOR]

The existing global tomographic methods result in different models due to different parametrization, scale resolution and theoretical approach. To test how current imaging techniques are limited by approximations in theory and by the inadequacy of data quality and coverage, it is necessary to perform a global-scale benchmark to understand the resolving properties of each specific imaging algorithm. In the framework of the Seismic wave Propagation and Imaging in Complex media: a European network (SPICE) project, it was decided to perform a benchmark experiment of global inversion algorithms. First, a preliminary benchmark with a simple isotropic model is carried out to check the feasibility in terms of acquisition geometry and numerical accuracy. Then, to fully validate tomographic schemes with a challenging synthetic data set, we constructed one complex anisotropic global model, which is characterized by 21 elastic constants and includes 3-D heterogeneities in velocity, anisotropy (radial and azimuthal anisotropy), attenuation, density, as well as surface topography and bathymetry. The intermediate-period (>32 s), high fidelity anisotropic modelling was performed by using state-of-the-art anisotropic anelastic modelling code, that is, coupled spectral element method (CSEM), on modern massively parallel computing resources. The benchmark data set consists of 29 events and three-component seismograms are recorded by 256 stations. Because of the limitation of the available computing power, synthetic seismograms have a minimum period of 32 s and a length of 10 500 s. The inversion of the benchmark data set demonstrates several well-known problems of classical surface wave tomography, such as the importance of crustal correction to recover the shallow structures, the loss of resolution with depth, the smearing effect, both horizontal and vertical, the inaccuracy of amplitude of isotropic S-wave velocity variation, the difficulty of retrieving the magnitude of azimuthal anisotropy and so on. The synthetic data set can be used to validate and calibrate new processing methodologies and has been made available to the scientific community at the Institut de Physique du Globe de Paris (IPGP) website ( ). Any group wishing to test their tomographic algorithm is encouraged to download the synthetic data. [ABSTRACT FROM AUTHOR]

The InSight mission landed on Mars on 11/26/2018. This is the first planetary mission deploying a complete geophysical observatory on another body than Earth after the Apollo Lunar Surface Experiments Package (ALSEP) deployed on the Moon during the Apollo program. It will provide the first ground truth constraints on interior structure of the planet. The Seismic Experiment for Interior Structure (SEIS) is one of the three primary scientific investigations, the two other ones being the Heat Flow and Physical Properties Package (HP3) and the Rotation and Interior Structure Experiment (RISE). SEIS is completed by the APSS experiment (InSight Auxiliary Payload Suite), one of which goal is to document the atmospheric source of seismic noise and signals. After a brief description of the SEIS experiment, we report the deployment process, including the evolution of the SEIS noise from on the deck measurements (with only SPs) toward on the ground (with both VBBs and SPs), without and finally with wind shield. We compare these noise levels to those obtained on Earth during tests, to those recorded on the Moon and to those predicted prior the landing. In all configurations, we identify the contribution of the lander noise and finally discuss what might remain in term of micro-seismic background, i.e. uncoherent seismic waves background.As proposed by several studies made prior the landing, atmospheric seismic signals on the ground are expected from turbulence in the planetary boundary layer or from dust devils, at both long period and short period. We expect also local time variation of the seismic noise as a consequence of weather activity as well as possible micro-seismic noise associated to trapped surface or body waves in the subsurface low velocity channel. We challenge these predictions with the data and discuss the events and spectrum identified with both the SEIS and APSS data. We finally compare them with modeling made with different subsurface structure. [ABSTRACT FROM AUTHOR]