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Using body wave arrival times from 31 seismic events recorded on Mars by the InSight mission, combined with topography and gravity field modeling, we constrained lateral variations of crustal thickness through a Bayesian inversion approach. The parameterization of the seismic structure relies on quantities that influence the thermochemical evolution of Mars, enabling the seismic velocities and densities in the different planetary envelopes to be consistently linked through common physical assumptions. Compared to a 1D structure, models with lateral variations of crustal thickness show two possible interpretations of the thermal evolution of Mars, with either a hot or cold scenario at the present‐day. We found the hot scenario to be more compatible with InSight's radiotracking data and the tidal Love number. We relocated the marsquakes and derived maps of seismicity recorded by InSight, which is mostly located along or North of the boundary between the Northern lowlands and the Southern highlands. Plain Language Summary: Thanks to the seismometer of the InSight mission, which recorded ground vibration measurements emanating from marsquakes and meteorite impacts during almost 4 years, the 1D interior structure of the crust, mantle, and core have been revealed. These models are mainly based on the assumption that the crustal thickness is similar everywhere on Mars. However, both the InSight lander and the most of the seismic events are located between the Northern lowlands and the Southern highlands where the crustal thickness varies widely, which can bias the interpretation of a 1D crustal model. In this study, combining the InSight seismic data with other independent geophysical measurements (topography and gravimetry data), we investigated to what extent the interior structure models are modified if lateral variations of crustal thickness are considered. Our results show that two different interpretations of Mars' thermal history can be considered, with either a hot or a cold scenario. We assessed the compatibility of our results with independent observations of oscillation of Mars' rotational axis, and found that the hot scenario is most likely. Key Points: We infer lateral variation of Martian crustal thickness using InSight seismic data combined with topography and gravity field modelingMarsquakes are relocated and maps of the seismicity recorded by InSight are proposedTwo families of models are found, leading to different interpretations of Mars' thermochemical evolution, with hot and cold scenarios [ABSTRACT FROM AUTHOR]

We measure group velocity dispersion of surface waves generated by two meteoroid impacts on Mars close to the lander of the InSight mission. This allows us to probe the crustal structure in the first few kilometers beneath the InSight lander. In combination with body wave arrival times from five impact events, we obtain direct seismic constraints on the seismic velocity of the crust in the vicinity of the InSight landing site. We confirm the existence of a uppermost low‐velocity layer with a mean thickness of ∼1.2 km, interpreted as layered volcanic materials, possibly interstratified with sedimentary and altered materials. Our joint inversion of surface and body waves shows a four‐layer model for the Martian crust, compatible with high‐ and low‐frequency P‐to‐S receiver functions estimated in previous studies. Plain Language Summary: The knowledge of the crustal structure of Mars is essential for understanding the formation and evolution of the planet. Thanks to the Very Broadband Seismometer of the InSight mission which landed on the surface of Mars (its operational life lasted almost four terrestrial years), seismic signals generated by meteoroid impacts have been recorded. Five craters have been identified by orbital imaging to be located within a circle of ∼250 km radius around the lander. For two of these meteoroid impacts, we measured surface waves for the first time, which are mostly sensitive to the crustal structure in the first kilometers below the InSight lander. Our surface wave analysis, in combination with other measurements, are compatible with a crustal model in the vicinity of the InSight lander made of four layers, with a shallow low velocity layer ∼1.2 km thick. We verified the compatibility of our results with independent observations from previous studies. Key Points: Group velocity dispersion generated by two meteoroid impacts (S0986c and S1034a) near the InSight landing site is measuredA shallow low‐velocity crustal layer of ∼1.2 km thickness explains both surface wave and body wave observationsA four‐layer crustal model is obtained, compatible with surface waves, body waves, and receiver function measurements [ABSTRACT FROM AUTHOR]

The ongoing InSight mission has recently deployed very broad band seismometers to record the Martian seismic activity. These recordings constitute the first seismic data set collected at the surface of Mars. This unique but sparse record compels for the development of new techniques tailored to make the best use of the specific context of single station-multiple events with several possible ranges of uncertainties on the event location. To this end, we conducted sets of Markov chain Monte Carlo inversions for the 1-D seismic structure of Mars. We compared two inversion techniques that differ from the nature of the parametrization on which they rely. A first classical approach based on a parametrization of the 1-D seismic profile using Bézier curves. A second, less conventional approach that relies on a parametrization in terms of quantities that influence the thermochemical evolution of the planet (mantle rheology, initial thermal state and composition), which accounts for 4.5 Gyr of planetary evolution. We considered several combinations of true model parameters to retrieve, and explored the influence of the type of seismic data (body waves with or without surface waves), the number of events and their associated epicentral distances and uncertainties, and the presence of potential constraints on Moho depth inferred from independent measurements/considerations (receiver functions and gravity data). We show that due to its inherent tighter constraints the coupled approach allows a considerably better retrieval of Moho depth and the seismic structure underneath it than the classical inversion, under the condition that the physical assumptions made in the coupled approach are valid for Mars. In addition, our tests indicate that in order to constrain the seismic structure of Mars with InSight data, the following independent conditions must be met: (1) The presence of surface waves triggered by an internal source to constrain the epicentral distance. (2) The presence of just a few well-localized impact sources, with at least one located at close epicentral distance (<5°) to illuminate independently the crust and the mantle. In addition to providing tighter constraints of Mars seismic structure, geodynamically constrained inversions allow one to reconstruct the thermochemical and rheological history of Mars until present. Therefore, even with a relatively small amount of large events and in absence of surface waves, constraining the present-day structure and long-term evolution of the red planet remains possible through the use of tailored hybrid inversion schemes. [ABSTRACT FROM AUTHOR]

SEIS, the seismometer of the InSight mission, which landed on Mars on 26 November 2018, is monitoring the seismic activity of the planet. The goal of the Mars Structure Service (MSS) is to provide, as a mission product, the first average 1‐D velocity model of Mars from the recorded InSight data. Prior to the mission, methodologies have been developed and tested to allow the location of the seismic events and estimation of the radial structure, using surface waves and body waves arrival times, and receiver functions. The paper describes these validation tests and compares the performance of the different algorithms to constrain the velocity model below the InSight station and estimate the 1‐D average model over the great circle path between source and receiver. These tests were performed in the frame of a blind test, during which synthetic data were inverted. In order to propagate the data uncertainties on the output model distribution, Bayesian inversion techniques are mainly used. The limitations and strengths of the methods are assessed. The results show the potential of the MSS approach to retrieve the structure of the crust and underlying mantle. However, at this time, large quakes with clear surface waves have not yet been recorded by SEIS, which makes the estimation of the 1‐D average seismic velocity model challenging. Additional locatable events, especially at large epicentral distances, and development of new techniques to fully investigate the data, will ultimately provide more constraints on the crust and mantle of Mars. Key Points: In the framework on the InSight mission, a synthetic seismogram using a 3‐D crust and a 1‐D velocity model below is proposedThis signal is used to present inversion methods, relying on different parameterizations, to constrain the 1‐D structure of MarsThe results demonstrate the feasibility of the strategy to retrieve VS in the crust, and a fairly good estimation of the Moho depth [ABSTRACT FROM AUTHOR]

With the recent successful landing and the ongoing deployment of its instruments, the InSight mission will soon provide the first series of Martian seismic recordings. Such data will allow the present-day deep structure of the planet to be revealed. While inverse methods are powerful tools to achieve this goal, they are prone to two main limitations: the large size of the parameter space to be explored, and the non-uniqueness of the solution. This is particularly true for spatially uneven and relatively small amounts of seismic recordings, as in the case of InSight, which consists of a single station, and a precious, but limited amount of expected Marsquakes.To better constrain the interior of Mars using the upcoming InSight recordings, we have developed a Monte-Carlo Markov-Chain inversion of seismic data, where the modeling of Mars' thermochemical history is part of the forward problem. Such a modeling accounts for the main Martian envelopes: an essentially metallic core surrounded by a convective silicate envelope, overlaid by a stagnant lithospheric lid. The latter includes a crust enriched in time-decaying, heat-producing radioactive elements. This thermo-chemical frame is integrated via a parametrized approach, allowing the long-term planetary evolution to be accurately modeled at a reasonable computational cost.Consequently, instead of varying independently seismological parameters along the inversion process (crustal thickness, core size, seismic velocities, etc.), our built-in geodynamic frame significantly reduces the parameter space, by self-consistently accounting for the interdependencies between various quantities: temperature, composition, rheology, and their influences on crustal thickness. Further constraints on these different physical parameters will come from recent measurements directly performed under Mars' interior P-T conditions. The resulting output parameters from the thermo-chemical modeling yield the seismic structure required for the inversion process. Our approach can also constrain the value of physical quantities inaccessible to direct measurements, such as the rheology of the Martian mantle. Finally, our method naturally yields the entire thermo-chemical history of Mars associated with each model.Our implementation has been benchmarked against analytical and numerical solutions in spherical geometry, and we successfully tested our inversion approach against synthetic data.We will present the details of our inversion method, together with its performances using synthetic data. Finally, we will apply our approach to the data that InSight instruments are expected to collect, in order to constrain the current state of Mars' interior, and to infer its long-term evolution. [ABSTRACT FROM AUTHOR]

An international team of researchers gathered, with the support of the International 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 knowledge 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. Following 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 estimate 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 demonstrate that the Apollo lunar seismic data mainly constrain the upper- and mid-mantle structure 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 gradient 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. [ABSTRACT FROM AUTHOR]

We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution. [ABSTRACT FROM AUTHOR]

Geophysical observations will provide key information about the inner structure of the planets and satellites and understanding the internal structure is a strong constraint on the bulk composition and thermal evolution of these bodies. Thus, geophysical observations are a key to uncovering the origin and evolution of the Moon. In this article, we propose the development of an autonomous lunar geophysical experiment package, composed of a suite of instruments and a central station with standardized interface, which can be installed on various future lunar missions. By fixing the interface between instruments and the central station, it would be possible to easily configure an appropriate experiment package for different missions. We describe here a series of geophysical instruments that may be included as part of the geophysical package: a seismometer, a magnetometer, a heat flow probe, and a laser reflector. These instruments will provide mechanical, thermal, and geodetic parameters of the Moon that are strongly related to the internal structure. We discuss the functionality required for future geophysical observations of the Moon, including the development of the central station that will be used commonly by different payloads. [ABSTRACT FROM AUTHOR]

The planned InSight mission will deliver a single seismic station containing 3-component broadband and short-period sensors to the surface of Mars in 2016. While much of the progress in understanding the Earth and Moon’s interior has relied on the use of seismic networks for accurate location of sources, single station approaches can be applied to data returned from Mars in order to locate events and determine interior structure. In preparation for the data return from InSight, we use a terrestrial dataset recorded at the Global Seismic Network station BFO, located at the Black Forest Observatory in Germany, to verify an approach for event location and structure determination based on recordings of multiple orbit surface waves, which will be more favorable to record on Mars than Earth due to smaller planetary radius and potentially lower background noise. With this approach applied to events near the threshold of observability on Earth, we are able to determine epicentral distance within approximately 1° (corresponding to ∼60 km on Mars), and origin time within ∼30 s. With back azimuth determined from Rayleigh wave polarization, absolute locations are determined generally within an aperture of 10°, allowing for localization within large tectonic regions on Mars. With these locations, we are able to recover Earth mantle structure within ±5% (the InSight mission requirements for martian mantle structure) using 1D travel time inversions of P and S travel times for datasets of only 7 events. The location algorithm also allows for the measurement of great-circle averaged group velocity dispersion, which we measure between 40 and 200 s to scale the expected reliable frequency range of the InSight data from Earth to Mars data. Using the terrestrial data, we are able to resolve structure down to ∼200 km, but synthetic tests demonstrate we should be able to resolve martian structure to ∼400 km with the same frequency content given the smaller planetary size. [ABSTRACT FROM AUTHOR]

Clues to a planet’s geologic history are contained in its interior structure, particularly its core. We detected reflections of seismic waves from the core-mantle boundary of Mars using InSight seismic data and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ± 40 kilometers. The large core implies a martian mantle mineralogically similar to the terrestrial upper mantle and transition zone but differing from Earth by not having a bridgmanite-dominated lower mantle. We inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core. The seismic core shadow as seen from InSight’s location covers half the surface of Mars, including the majority of potentially active regions—e.g., Tharsis—possibly limiting the number of detectable marsquakes. [ABSTRACT FROM AUTHOR]

For 2 years, the InSight lander has been recording seismic data on Mars that are vital to constrain the structure and thermochemical state of the planet. We used observations of direct (P and S) and surface-reflected (PP, PPP, SS, and SSS) body-wave phases from eight low-frequency marsquakes to constrain the interior structure to a depth of 800 kilometers. We found a structure compatible with a low-velocity zone associated with a thermal lithosphere much thicker than on Earth that is possibly related to a weak S-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow. [ABSTRACT FROM AUTHOR]

Several seismic experiments were deployed on the Moon by the astronauts during the Apollo missions. The experiments began in 1969 with Apollo 11, and continued with Apollo 12, 14, 15, 16 and 17. Instruments at Apollo 12, 14, 15, 16 and 17 remained operational until the final transmission in 1977. These remarkable experiments provide a valuable resource. Now is a good time to review this resource, since the InSight mission is returning seismic data from Mars, and seismic missions to the Moon and Europa are in development from different space agencies. We present an overview of the seismic data available from four sets of experiments on the Moon: the Passive Seismic Experiments, the Active Seismic Experiments, the Lunar Seismic Profiling Experiment and the Lunar Surface Gravimeter. For each of these, we outline the instrumentation and the data availability. We show examples of the different types of moonquakes, which are: artificial impacts, meteoroid strikes, shallow quakes (less than 200 km depth) and deep quakes (around 900 km depth). Deep quakes often occur in tight spatial clusters, and their seismic signals can therefore be stacked to improve the signal-to-noise ratio. We provide stacked deep moonquake signals from three independent sources in miniSEED format. We provide an arrival-time catalog compiled from six independent sources, as well as estimates of event time and location where available. We show statistics on the consistency between arrival-time picks from different operators. Moonquakes have a characteristic shape, where the energy rises slowly to a maximum, followed by an even longer decay time. We include a table of the times of arrival of the maximum energy t max and the coda quality factor Q c . Finally, we outline minimum requirements for future lunar missions to the Moon. These requirements are particularly relevant to future missions which intend to share data with other agencies, and set out a path for an International Lunar Network, which can provide simultaneous multi-station observations on the Moon. [ABSTRACT FROM AUTHOR]

Despite its ground installation at about 1.5 meter from the lander, SEIS (Seismic Experiment for Interior Structure) will be sensitive to the ground displacement generated by the lander, in addition to direct forces from the lander propagating along the tether. This lander noise is also expected in the VBB (Very Broad Band seismometers) bandwidth, including below the gravest resonance mode of the lander, expected close or below 10 Hz. In the VBB bandwidth, the lander deck acceleration has been monitored by the SPs (Short Period seismometers) when the latter were operating on it. These measurements provide key constrains on the level of deck acceleration and possibly deck rotation and can therefore be used to predict the forces generated by the lander on the ground and to compare them with the observations made by the SEIS VBBs on the ground. We use formalism developed by Fayon et al. (2017) to model the lander and its 3 feet and complete the approach of Murdoch et al (2017) by adding the torques generated on each foot by the lander rotations, which might likely be important in the bandwidth of the VBB sensors, e.g. [0-10 Hz]. We then identify on the ground VBB signals the largest resonances in the 0-10 Hz bandwidth, including in term of polarized signals on the 3 axes components and analyze their amplitude as a function of wind level and pressure fluctuation. For all the identified VBB resonances, we repeat the analysis using the SP data on the deck. We present preliminary results and tests on a noise rejection algorithm, in order to improve the capability of the VBBs to detect non-lander atmospheric signals and seismic signals in the DC-10 Hz bandwidth. We finally conclude by discussing the opportunity offered by this lander signal to better characterize the wind flow on the lander. [ABSTRACT FROM AUTHOR]

Exploring the internal structure and the dynamics of our solar system is mandatory to understand the behavior of our universe and its origin. One of the tools chosen by NASA is seismology, particularly in order to constrain the deep interior structure of the red planet via the Insight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) mission that was successfully landed on November 26th, 2018 in Elysium Planitia. However, planetary seismology is still far from providing models with high precision and calculation speed. Thus, this study is one of the first attempts to model the Martian interior structure using a seismic waveform inversion technique : the Machine Learning and the Pattern Search algorithm by resolving a nonlinear global optimization problem.It's a new revolutionary mathematical tool for seismology and inverse problem in general as it gives a better understanding of blinded or burred problems like our case.For that, before applying it to the incoming InSight data provided by the seismometer SEIS (the Seismic Experiment for Interior Structure), we need to ensure its efficiency through several tests. Therefore, we will focus on the inversion sensibility error by comparing the resulting inverted crustal model obtained using this new method to the existing models provided by the SEIS team using other tools like Markov Chain Monte Carlo (McMC). This technique will be applied to the MSS blind test data computed by the InSight collaborators. The aim is to constrain the epicentral distance, the depth and origin time of the seismic event, as well as the seismic velocity profiles and the attenuation, and to compare it with existing methods developed by the InSight science team. [ABSTRACT FROM AUTHOR]

The InSight lander will deliver geophysical instruments to Mars in 2018, including seismometers installed directly on the surface (Seismic Experiment for Interior Structure, SEIS). Routine operations will be split into two services, the Mars Structure Service (MSS) and Marsquake Service (MQS), which will be responsible, respectively, for defining the structure models and seismicity catalogs from the mission. The MSS will deliver a series of products before the landing, during the operations, and finally to the Planetary Data System (PDS) archive. Prior to the mission, we assembled a suite of a priori models of Mars, based on estimates of bulk composition and thermal profiles. Initial models during the mission will rely on modeling surface waves and impact-generated body waves independent of prior knowledge of structure. Later modeling will include simultaneous inversion of seismic observations for source and structural parameters. We use Bayesian inversion techniques to obtain robust probability distribution functions of interior structure parameters. Shallow structure will be characterized using the hammering of the heatflow probe mole, as well as measurements of surface wave ellipticity. Crustal scale structure will be constrained by measurements of receiver function and broadband Rayleigh wave ellipticity measurements. Core interacting body wave phases should be observable above modeled martian noise levels, allowing us to constrain deep structure. Normal modes of Mars should also be observable and can be used to estimate the globally averaged 1D structure, while combination with results from the InSight radio science mission and orbital observations will allow for constraint of deeper structure. [ABSTRACT FROM AUTHOR]

Like all NASA missions, InSight's data will be archived at the Planetary Data System (PDS), a long-term digital data archive. This includes data from SEIS, the first seismometer deployed on the Martian ground (40 years after the Viking deck-mounted instruments), as well as those of the Auxiliary Payload Sensors Suite (APSS). For SEIS, the distributed data are those of the very broad-band (VBB), short-period (SP) sensors, SEIS electronics, leveling system, and selected lander telemetry channels.SEIS and APSS data are received from the spacecraft in raw telemetry packets and converted to both SEED format files and ASCII tables (GeoCSV) for analysis and archiving. APSS data in SEED format will permit straightforward data comparison. Both data sets will then be delivered to the Mars SEIS Data Service (MSDS) at IPGP Data Center. IPGP maintains the SEIS data portal, which will become open-access a week prior to the first public data distribution. MSDS will also deliver SEIS data to PDS for archiving and to IRIS as a second data portal. IRIS, an InSight educational partner, has the goal of engaging students with seismic data from Mars. The IRIS Data Management Center and MSDS will make data from the seismometer available to students, the international seismological community, and the public. Data for schools will be distributed via several international "seismo@school" projects.The initial release of raw data archive products to the PDS, covering the period from landing to the start of the science monitoring phase, will occur within 3 months of the start of the science monitoring phase (anticipated April 2019), with calibrated products and SPICE kernels following a month later. After these initial releases, the calibrated and SPICE data will be released by the PDS every 3 months, beginning in July 2019. Public release of "uncertified" seismic velocity data via IRIS will start about 7 months after the start of the science monitoring phase and will be made every 4 weeks. [ABSTRACT FROM AUTHOR]

The NASA InSight mission to Mars successfully landed on November 26th, 2018 in Elysium Planitia. It aims to characterize the seismic activity and the internal structure of Mars. In this study we focus on the Cerberus Fossae fault system, which is the closest and largest tectonic structure (~1200 km long) near the landing site of the InSight mission. It is formed by four to five main grabens located on the Southeast of the Elysium Mons volcanic rise. The faults tectonic activity is expected to generate medium-sized marsquakes (Mw > 3) during the nominal mission. In order to better constrain these potential seismic sources, we performed a detailed mapping of the entire fault system based on high resolution satellite images (e.g. CTX, HiRISE) and calculated DEMs. The refined cartography presents a wide range of fault and fracture patterns. Graben widths measurements show a strong correlation with existing fault throws measurements. Altogether they give some insights on the direction of long-term propagation of the fault system but also on fault dips at depth and how the grabens are rooted in the shallow part of the crust. Moreover, the exceptional preservation of the grabens allows to detect up to four scales of segmentation, each formed by a similar number of 3-4 segments/subsegments. This generic distribution of the number of segments is comparable to continental faults on Earth. Fault segmentation can be used to highlight local stress concentrations along the fault and thus anticipate locations of potential marsquakes. We finally compare our surface analysis of fault traces with numerical simulations of the regional crustal stress field of the Elysium Planitia area using joint analysis of gravity and topographic data truncated to spherical harmonic models. [ABSTRACT FROM AUTHOR]

Authors:T. Kawamura(1), N. C. Schmerr(2), L. Margerin(3), M. van Driel(4), R. Garcia(5), F. Karakostas(1,2), Benoit Tauzin (6), M. Drilleau(1), P. Lognonné(2),Affiliations:1 Institut de Physique du Globe de Paris2 University of Maryland3 CNRS / Université de Toulouse 4 ETH Zurich5 ISAE-SUPAERO6 Université de LyonTitle:Measuring the Scattering and Atteunation of Seismic Waves in Mars with the InSight Seismometers. Abstract: The amplitudes of seismic waves decrease over distance due frequency dependent energy loss via scattering and attenuation. Scattering, or extrinsic attenuation, is dependent upon the size, strength, and abundance of elastic heterogeneities within the medium. Intrinsic attenuation results from dissipation due to anelastic processes and internal friction between molecules and defects within crystal lattices. Both forms of attenuation are described using the seismic quality factor, Q. Scattering can arise from compositional heterogeneities, mechanical boundaries (such as fractures, cracks, veins, cavities), and other major non-radial changes in material properties of an object. Intrinsic attenuation is tied to grain boundary processes, crystal defects, fluid-filled cracks, and other dissipative viscoelastic processes. Attenuation is vital for understanding the detectability, travel times, and propagation properties of seismic waves, as well as the properties of the interior of a world. The Interior Exploration using Seismic Investigations Geodesy and Heat Transport (InSight) Seismic Experiment for Interior Structure (SEIS) has placed a very broadband (VBB) and short period (SP) seismometers on Mars that allows us to investigate the fundamental geophysical process of seismic attenuation at Mars, which is expected to have properties falling between the Earth and the Moon. In the Earth, attenuation by seismic scattering is found to be relatively weak, and is typically confined to small-scale compositional heterogeneities in the crust, lithosphere, and mantle. Intrinsic attenuation varies throughout the Earth, and is especially high where fluids, elevated temperatures, and changes in grain size are present. On the Moon, seismic scattering is pervasive in the highly fractured and dry crust and uppermost mantle, and intrinsic attenuation is large in the deep interior. At present, the total Q, layering in Q, and relative proportion of seismic scattering to intrinsic attenuation within Mars remains unconstrained. [ABSTRACT FROM AUTHOR]

Mars atmospheric pressure variations induce ground deformations that are the main source of environmental noise on the InSight SEIS instrument. Phenomena generating pressure variations, such as meteorological wavefronts, gravity waves, convective vortices and small-scale turbulence are covering the whole frequency range of SEIS broadband seismometers. These signals impact the capability of SEIS sensors to detect seismic waves propagating in Mars interior. However, the relation between pressure variations measured by the InSight pressure sensor and ground movements measured by SEIS being essentially linear, it is possible to invert both signals to find the transfer function between pressure and ground motion. Then, pressure generated ground movements can be substracted from SEIS records in order to improve their sensitivity to seismic waves. The transfer function, usually called compliance, depends on the ground properties. Thus, the decorrelation of SEIS records from pressure effects will also allow us to constrain the subsurface properties at the InSight landing site.Our study compares two different pressure decorrelation methods applied to Mars synthetic data, and records by both short period and very broadband SEIS sensors. The pressure-decorrelation methods are presented and their differences in terms of underlying assumptions and implementations are explained. Their performances and drawbacks, analyzed on realistic synthetic datasets, are discussed. We plan to apply these methods to real Mars data and use them to retrieve the ground compliance at the InSight landing site over a broad frequency range. Accordingly, we expect to extract elastic properties of the subsurface through the compliance measurements. Wind measurements by the TWINS wind sensor will be integrated in order to separate the effects of various atmospheric phenomena. This sensor is almost identical to the Rover Environmental Monitoring Station sent to Mars as part of the Mars Science Laboratory (MSL), which operated even after the damage suffered during the MSL landing for more than two Martian years. Thus, wind measured by TWINS will provide valuable inputs to the decorrelation on the InSight SEIS instrument. Finally, the variations of decorrelation performances and compliance measurements with the diurnal Mars cycle will be analyzed. [ABSTRACT FROM AUTHOR]

The Interior exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) Mission will focus on Mars' interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moon's much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of 3-10× relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars. [ABSTRACT FROM AUTHOR]

The InSight mission to Mars is well underway and will be the first mission to acquire seismic data from a planet other than Earth. In order to maximise the science return of the InSight data, a multifaceted approach will be needed that seeks to investigate the seismic data from a series of different frequency windows, including body waves, surface waves, and normal modes. Here, we present a methodology based on globally-averaged models that employs the long-period information encoded in the seismic data by looking for fundamental-mode spheroidal oscillations. From a preliminary analysis of the expected signal-to-noise ratio, we find that normal modes should be detectable during nighttime in the frequency range 5-15 mHz. For improved picking of (fundamental) normal modes, we show first that those are equally spaced between 5-15 mHz and then show how this spectral spacing, obtained through autocorrelation of the Fourier-transformed time series can be further employed to select normal mode peaks more consistently. Based on this set of normal-mode spectral frequencies, we proceed to show how this data set can be inverted for globally-averaged models of interior structure (to a depth of ∼250km), while simultaneously using the resultant synthetically-approximated normal mode peaks to verify the initial peak selection. This procedure can be applied iteratively to produce a "cleaned-up" set of spectral peaks that are ultimately inverted for a "final" interior-structure model. To investigate the effect of three-dimensional (3D) structure on normal mode spectra, we constructed a 3D model of Mars that includes variations in surface and Moho topography and lateral variations in mantle structure and employed this model to compute full 3D waveforms. The resultant time series are converted to spectra and the inter-station variation hereof is compared to the variation in spectra computed using different 1D models. The comparison shows that 3D effects are less significant than the variation incurred by the difference in radial models, which suggests that our 1D approach represents an adequate approximation of the global average structure of Mars. [ABSTRACT FROM AUTHOR]