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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.

Since February 2019, NASA's InSight lander is recording seismic signals on the planet Mars, which, for the first time, allows to observe ongoing tectonic processes with geophysical methods. A number of Marsquakes have been located in the Cerberus Fossae graben system in Elysium Planitia and further west, in the Orcus Patera depression. We present a first study of the focal mechanisms of three well‐recorded events (S0173a, S0183a, S0235b) to determine the processes dominating in the source region. We infer for all three events a predominantly extensional setting. Our method is adapted to the case of a single, multicomponent receiver and based on fitting waveforms of P and S waves against synthetic seismograms computed for the initial crustal velocity model derived by the InSight team. We explore the uncertainty due to the single‐station limitation and find that even data recorded by one station constrains the mechanisms (reasonably) well. For the events in the Cerberus Fossae region (S0173a, S0235b) normal faulting with a relatively steep dipping fault plane is inferred, suggesting an extensional regime mainly oriented E‐W to NE‐SW. The fault regime in the Orcus Patera region is not determined uniquely because only the P wave can be used for the source inversion. However, we find that the P and weak S waves of the S0183a event show similar polarities to the event S0173, which indicates similar fault regimes. Plain Language Summary: As time passes, the mysterious interior of Mars is slowly being unraveled due to the detection and analysis of Marsquakes recorded with a seismograph carried by the InSight lander. Close to 400 Marsquakes have so far been identified, yet only a handful of those show similarities to earthquakes. Those earth‐like events are located near the Cerberus Fossae and Orcus Patera regions. We take advantage of the similarity between Marsquakes and earthquakes and apply a methodology developed for earthquake characterization before seismic recorders became abundant on Earth. We find that the Marsquakes in these source regions are dominated by extensional rather than compressing features. This is important information to further understand what causes Marsquakes. Key Points: We infer the tectonic setting in Cerberus Fossae on Mars by seismic source inversionWe present a robust inversion strategy for single‐station moment tensor inversionThree Marsquakes recorded by InSight reveal a predominantly normal faulting regime [ABSTRACT FROM AUTHOR]

We image the thermochemical structure of crust and mantle underneath the North American continent by inverting recordings of P‐to‐s (Ps) and S‐to‐p (Sp) converted seismic body waves (receiver functions [RFs]). Through careful data selection and processing, we construct a multifrequency Ps (5‐, 8‐, and 10 ‐s) and Sp (10‐ and 15‐ s) RF data set from USArray recordings. The inversion is interfaced with petrological phase equilibria computations to build self‐consistent radial seismic velocity and density models for RF waveform simulations. Inverted models are combined through back‐projection along converted raypaths and interpolation to tomographic images of crust and mantle structure. Through clustering analysis we identify three major tectonic regions based on mantle thermochemical and seismic structure: the tectonically active West (TAW), the central transition region (CTR), and the cratonic‐orogenic East (COE). TAW is chemically more fertile with a Mg# ∼ 0.90 (molar Mg# = Mg/(Mg + Fe)) and characterized by an elevated mantle potential temperature of 1490 ± 27°C relative to COE, which is chemically more depleted (Mg# ∼ 0.91) and colder (1419 ± 27°C). CTR is intermediate to TAW and COE. We find significant thermochemically induced topography associated with the base of the lithosphere (±90 km), while the mantle transition zone is mostly influenced by thermally induced topography on the 410‐km discontinuity (±15 km). In contrast, the 660‐km discontinuity, where variations are only ±5 km, reflects a more complex thermochemical interplay. To place the results in a tectonic context, thermobarometric estimates from basaltic rocks across the western United States are integrated with the seismic inversions to produce a thermal model of the underlying mantle. Key Points: We describe a method for inverting multifrequency Ps and Sp receiver functions for mantle thermochemical structureWe distinguish tectonic regions based on thermochemical characteristics across the United States from the active West to the cratonic‐orogenic EastWe observe strong thermochemically induced and interrelated topographic variations of the lithospheric base and the 410‐km discontinuity [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]

The InSight mission will land a single seismic station on Mars in November 2018, and the resultant seismicity catalog will be a key component for studies aiming to understand the interior structure of the planet. Here, we present a preliminary version of the web services that will be used to distribute the event and station metadata in practice, employing synthetic seismograms generated for Mars using a catalog of expected seismicity. Our seismicity catalog consists of 120 events with double-couple source mechanisms only. We also provide Green's functions databases for a total of 16 structural models, which are constructed to reflect one-dimensional thin (30 km) and thick (80 km) Martian crust with varying seismic wave speeds and densities, combined with two different profiles for temperature and composition for the mantle. Both the Green's functions databases and the precomputed seismograms are accessible online. These new utilities allow the researchers to either download the precomputed synthetic waveforms directly, or produce customized data sets using any desired source mechanism and event distribution via our servers. [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]