Seismic energy envelopes in volcanic media : in need of boundary conditions

Peer reviewedPublisher PD

Controlling Light Through Optical Disordered Media : Transmission Matrix Approach

We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and we study the effect of noise on the reconstruction method. We also extracted from the TM informations about the statistical properties of the medium and the light transport whitin it. In particular, we are able to isolate the contributions of the Memory Effect (ME) and measure its attenuation length

Multi-scale investigation of the InSight landing site, on Mars, using one-station seismology

The internal structure of a planet provides constraints for understanding its evolution and dynamics. In November 2018, the InSight spacecraft landed on Mars and deployed a set of geophysical instruments, including one seismological station. In this work, the subsurface structure at the InSight landing site (ILS) is explored, from the shallow subsurface to crustal depths, by applying single-station seismological techniques (SST) on martian ambient vibrations and seismic events data. The shallow subsurface at the ILS, in the order of meters, is investigated using the horizontal-to-vertical spectral ratios (HVSR) from the coda of martian seismic events. Assuming a fully diffuse wavefield, a nonlinear inversion using the conditional Neighbourhood Algorithm (NA) allowed to map the shallow subsurface at the ILS. Due to the non-uniqueness problem, different sets of models are retrieved. The 8 Hz HVSR peak can be explained by a Rayleigh wave resonance due to a shallow high-velocity layer, while the 2.4 Hz trough is explained by a P-wave resonance due to a buried low-velocity layer. The kilometer-scale subsurface was constrained by Rayleigh wave ellipticity measurements from large martian seismic events. The ellipticity measurements (0.03-0.07 Hz) were jointly inverted with P-to-s Receiver Functions and P-wave lag times from autocorrelations, to provide a subsurface model for the martian crust at the ILS. The joint inversion allowed the thickness and velocities of a new surface layer, previously proposed only conceptually, to be constrained by multiple seismological data. The HVSR in the 0.06-0.5 Hz frequency range from the coda of S1222a, the largest event ever recorded on Mars, suggests a gradual transition from shallow to crustal depths and consolidates the group of shallow subsurface models with the largest shear-wave velocities as the most compatible with the crustal structure. A comprehensive multi-scale model of the ILS subsurface is proposed. The ILS is characterized by the emplacement of a low-velocity regolith/coarse ejecta layer over a high-velocity Amazonian fractured lava flow (~2 km/s, ~30 m thick). A buried Late Hesperian-Amazonian sedimentary layer is deposited below (~450 m/s, ~30 m thick), underlain by a heavily weathered Early Hesperian lava flow. The latter overlays a thick, likely Noachian sedimentary layer that extends to a depth of 2-3 km. This shallow structure forms the first crustal layer derived from the joint inversion. Deeper crustal layers are consistent with other reported ILS models, with intracrustal discontinuities at 8-12 km and 18-23 km depth. The Moho depth at the ILS is found at 35-45 km depth. Shear-wave velocities above ~20 km depth are lower than 2.5 km/s, slower than in other regions of Mars, suggesting a higher alteration due to local processes or a different origin of the upper crust at the ILS. The proposed model is consistent with the geologic history of Mars and other independent observations, confirming the great potential of SST for multi-scale investigation of, e.g., other planetary bodies or understudied regions on Earth

Study of the Ti-44(alpha, p)V-47 reaction and implications for core collapse supernovae

Peer reviewe

Lunar Seismology: An Update on Interior Structure Models

An international team of researchers gathered, with the support of the Interna- tional Space Science Institute (ISSI), (1) to review seismological investigations of the lunar interior from the Apollo-era and up until the present and (2) to re-assess our level of knowl- edge and uncertainty on the interior structure of the Moon. A companion paper (Nunn et al. in Space Sci. Rev., submitted) reviews and discusses the Apollo lunar seismic data with the aim of creating a new reference seismic data set for future use by the community. In this study, we first review information pertinent to the interior of the Moon that has become available since the Apollo lunar landings, particularly in the past ten years, from orbiting spacecraft, continuing measurements, modeling studies, and laboratory experiments. Fol- lowing this, we discuss and compare a set of recent published models of the lunar interior, including a detailed review of attenuation and scattering properties of the Moon. Common features and discrepancies between models and moonquake locations provide a first esti- mate of the error bars on the various seismic parameters. Eventually, to assess the influence of model parameterisation and error propagation on inverted seismic velocity models, an inversion test is presented where three different parameterisations are considered. For this purpose, we employ the travel time data set gathered in our companion paper (Nunn et al. in Space Sci. Rev., submitted). The error bars of the inverted seismic velocity models demon- strate that the Apollo lunar seismic data mainly constrain the upper- and mid-mantle struc- ture to a depth of ∼1200 km. While variable, there is some indication for an upper mantle low-velocity zone (depth range 100–250 km), which is compatible with a temperature gradi- ◦ent around 1.7 C/km. This upper mantle thermal gradient could be related to the presence of the thermally anomalous region known as the Procellarum Kreep Terrane, which contains a large amount of heat producing elements

Empirical H/V spectral ratios at the InSight landing site and implications for the martian subsurface structure

The horizontal-to-vertical (H/V) spectral ratio inversion is a traditional technique for deriving the local subsurface structure on Earth. We calculated the H/V from the ambient vibrations at different wind levels at the InSight landing site, on Mars, and also computed the H/V from the S-wave coda of the martian seismic events (marsquakes). Different H/V curves were obtained for different wind periods and from the marsquakes. From the ambient vibrations, the recordings during low-wind periods are close to the instrument self-noise level. During high-wind periods, the seismic recordings are highly contaminated by the interaction of the lander with the wind and the martian ground. Therefore, these recordings are less favourable for traditional H/V analysis. Instead, the recordings of the S-wave coda of marsquakes were preferred to derive the characteristic H/V curve of this site between 0.4 and 10 Hz. The final H/V curve presents a characteristic trough at 2.4 Hz and a strong peak at 8 Hz. Using a full diffuse wavefield approach as the forward computation and the Neighbourhood Algorithm as the sampling technique, we invert for the 1-D shear wave velocity structure at the InSight landing site. Based on our inversion results, we propose a strong site effect at the InSight site to be due to the presence of a shallow high-velocity layer (SHVL) over low-velocity units. The SHVL is likely placed below a layer of coarse blocky ejecta and can be associated with Early Amazonian basaltic lava flows. The units below the SHVL have lower velocities, possibly related to a Late Hesperian or Early Amazonian epoch with a different magmatic regime and/or a greater impact rate and more extensive weathering. An extremely weak buried low velocity layer (bLVL) between these lava flows explains the data around the 2.4 Hz trough, whereas a more competent bLVL would not generate this latter feature. These subsurface models are in good agreement with results from hammering experiment and compliance measurements at the InSight landing site. Finally, this site effect is revealed only by seismic events data and explains the larger horizontal than vertical ground motion recorded for certain type of marsquakes.The authors acknowledge National Aeronautics and Space Administration (NASA), Centre National D’études Spatiales (CNES), their partner agencies and institutions (United Kingdom 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 [IPGP]—Centre National de la Recherche Scientifique-École Normale Supérieure [CNRS], Eldgenössische Technische Hochschule Zürich [ETHZ], Imperial college [IC], Max Planck Institute for Solar System Research [MPS-MPG]), and the flight operations team at JPL, SEIS on Mars Operation Center (SISMOC), Mars SEIS Data Service (MSDS), Incorporated Research Institutions for Seismology–Data Management Center (IRIS-DMC) and Planetary Data System (PDS) for providing 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-0617–02, and (3) ETH + 02 19–1: Planet MARS. The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This is the InSight contribution number 268

Constraints for the Martian Crustal Structure From Rayleigh Waves Ellipticity of Large Seismic Events

For the first time, we measured the ellipticity of direct Rayleigh waves at intermediate periods (15-35 s) on Mars using the recordings of three large seismic Martian events, including S1222a, the largest event recorded by the InSight mission. These measurements, together with P-to-s receiver functions and P-wave reflection times, were utilized for performing a joint inversion of the local crustal structure at the InSight landing site. Our inversion results are compatible with previously reported intra-crustal discontinuities around 10 and 20 km depths, whereas the preferred models show a strong discontinuity at ~37 km, which is interpreted as the crust-mantle interface. Additionally, we support the presence of a shallow low-velocity layer of 2-3 km thickness. Compared to nearby regions, lower seismic wave velocities are derived for the crust, suggesting a higher porosity or alteration of the whole local crust

The Polarization of Ambient Noise on Mars

Seismic noise recorded at the surface of Mars has been monitored since February 2019, using the InSight seismometers. This noise can reach −200 dB. It is 500 times lower than on Earth at night and it increases of 30 dB during the day. We analyze its polarization as a function of time and frequency in the band 0.03–1 Hz. We use the degree of polarization to extract signals with stable polarization independent of their amplitude and type of polarization. We detect polarized signals at all frequencies and all times. Glitches correspond to linear polarized signals which are more abundant during the night. For signals with elliptical polarization, the ellipse is in the horizontal plane below 0.3 Hz. In the 0.3-1Hz high frequency band (HF) and except in the evening, the ellipse is in the vertical plane and the major axis is tilted. While polarization azimuths are different in the two frequency bands, they both vary as a function of local hour and season. They are also correlated with wind direction, particularly during the daytime. We investigate possible aseismic and seismic origins of the polarized signals. Lander or tether noise can be discarded. Pressure fluctuations transported by wind may explain part of the HF polarization but not the tilt of the ellipse. This tilt can be obtained if the source is an acoustic emission coming from high altitude at critical angle. Finally, in the evening when the wind is low, the measured polarized signals may correspond to the seismic wavefield of the Mars background noise

A Cerberus Fossae Seismic Network

Scientific Rationale: It is by now widely accepted that Mars had a wet and periodically warm past in the Noachian e.g. [1], but it is still open whether liquid water has played any role geologically in recent times or is even present in significant amounts near the surface today e.g. [2]. One key young area are the Cerberus Fossae (C.F.), a system of < 10 Ma old, 1200 km long grabens in Eastern Elysium Planitia. They connect to sediments in Athabasca Valles that have been interpreted as fluvial sediments from a frozen water layer molten by volcanism 8-10 Ma ago [3], but could alternatively be explained by very low viscosity lava as well [4

Measurement of 19Ne spectroscopic properties via a new method of inelastic scattering to study novae

The accuracy of the predictions of the γ flux produced by a classical nova during the first hours after the outburst is limited by the uncertainties on several reaction rates, including the 18F(p,α)15O one. Better constraints on this reaction rate can be obtained by determining the spectroscopic properties of the compound nucleus 19Ne. This was achieved in a new inelastic scattering method using a 19Ne radioactive beam (produced by the GANIL-SPIRAL 1 facility) impinging onto a proton target. The experiment was performed at the VAMOS spectrometer. In this article the performances (excitation energy range covered and excitation energy resolution) and limitations of the new technique are discussed. Excitation energy resolution of σ = 33 keV and low background were obtained with this inverse kinematics method, which will allow extracting the spectroscopic properties of 19Ne