Preparing for InSight: An Invitation to Participate in a Blind Test for Martian Seismicity

Clinton, John; Giardini, Domenico; Lognonné, Philippe; Banerdt, Bruce; Driel, Martin van; Drilleau, M.; Murdoch, Naomi; Panning, M. P.; Garcia, Raphaël; Mimoun, David; Golombek, M.; Tromp, Jeroen; Weber, R. C.; Böse, Maren; Ceylan, Savas; Daubar, I. J.; Kenda, B.; Khan, Amir; Perrin, Ludovic; Spiga, Aymeric

doi:10.1785/0220170094

Cited by 40 publications

(55 citation statements)

References 51 publications

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“…The same arguments concern determination of core size, which is otherwise detectable using normal modes (Okal & Anderson, ) or core‐reflected (e.g., PcP and ScS) and core‐refracted waves (e.g., PKP and SKS) (Helffrich, ). While seismic analyses in preparation for InSight have been and are currently undertaken (e.g., Böse et al, ; Bozdağ et al, ; Ceylan et al, ; Clinton et al, ; Goins & Lazarewicz, ; Khan et al, ; Larmat et al, ; Lognonné et al, ; Okal & Anderson, ; Panning et al, ; Solomon et al, ; Teanby & Wookey, ; Zharkov & Gudkova, ), we leave it for a future study to consider seismic predictions of the models proposed here in more detail.…”

Section: Resultsmentioning

confidence: 99%

A Geophysical Perspective on the Bulk Composition of Mars

et al. 2018

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We invert the Martian tidal response and mean mass and moment of inertia for chemical composition, thermal state, and interior structure. The inversion combines phase equilibrium computations with a laboratory‐based viscoelastic dissipation model. The rheological model, which is based on measurements of anhydrous and melt‐free olivine, is both temperature and grain size sensitive and imposes strong constraints on interior structure. The bottom of the lithosphere, defined as the location where the conductive geotherm meets the mantle adiabat, occurs deep within the upper mantle (∼200–400 km depth) resulting in apparent upper mantle low‐velocity zones. Assuming an Fe‐FeS core, our results indicate (1) a mantle with a Mg# (molar Mg/Mg+Fe) of ∼0.75 in agreement with earlier geochemical estimates based on analysis of Martian meteorites; (2) absence of bridgmanite‐ and ferropericlase‐dominated basal layer; (3) core compositions (15–18.5 wt% S), core radii (1,730–1,840 km), and core‐mantle boundary temperatures (1620–1690°C) that, together with the eutectic‐like core compositions, suggest that the core is liquid; and (4) bulk Martian compositions with a Fe/Si (weight ratio) of 1.66–1.81. We show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters. Specifically, we find that the inversion results are largely reproducible by stagnant lid convection models for a range of initial viscosities (∼1018–1020 Pa s) and radioactive element partitioning between crust and mantle around 0.01–0.1. The geodynamic models predict a mean surface heat flow between 15 and 25 mW/m2.

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Section: Resultsmentioning

confidence: 99%

A Geophysical Perspective on the Bulk Composition of Mars

et al. 2018

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“…Attenuation curves showing peak acceleration amplitude as a function of distance for two Mars interior structure models with Instaseis databases computed for the Marsquake Service blind test (Clinton et al, ; Rivoldini et al, ). The two models have very different crustal structure, which generally creates the largest contrast in predicted amplitudes over the range of models considered.…”

Section: Probability Of Detecting Events On Mars With Only On‐deck Opmentioning

confidence: 99%

On‐Deck Seismology: Lessons from InSight for Future Planetary Seismology

et al. 2020

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Before deploying to the surface of Mars, the short-period (SP) seismometer of the InSight mission operated on deck for a total of 48 hr. This data set can be used to understand how deck-mounted seismometers can be used in future landed missions to Mars, Europa, and other planetary bodies. While operating on deck, the SP seismometer showed signals comparable to the Viking-2 seismometer near 3 Hz where the sensitivity of the Viking instrument peaked. Wind sensitivity showed similar patterns to the Viking instrument, although amplitudes on InSight were ∼80% larger for a given wind velocity. However, during the low-wind evening hours, the instrument noise levels at frequencies between 0.1 and 1 Hz were comparable to quiet stations on Earth, although deployment to the surface below the Wind and Thermal Shield lowered installation noise by roughly 40 dB in acceleration power. With the observed noise levels and estimated seismicity rates for Mars, detection probability for quakes for a deck-mounted instrument is low enough that up to years of on-deck recordings may be necessary to observe an event. Because the noise is dominated by wind acting on the lander, though, deck-mounted seismometers may be more practical for deployment on airless bodies, and it is important to evaluate the seismicity of the target body and the specific design of the lander. Detection probabilities for operation on Europa reach over 99% for some proposed seismicity models for a similar duration of operation if noise levels are comparable to low-wind time periods on Mars. Plain Language SummaryIn the Viking-2 mission in the late 1970s, a seismometer was used on the deck of the lander but only saw one event that could be interpreted as a signal like earthquakes on Earth. Because of this, the InSight mission put their seismic instrument on the ground and covered it up to keep the wind from blowing on it. But we can use the time period where it was turned on before getting put on the ground to figure out whether future missions could do seismology without placing it on the ground. We find that the wind blowing on InSight gave us similar signals to the Viking lander, even though InSight had a better instrument. When we use models of how many quakes should be on Mars, we find that keeping the instrument on deck makes it hard to see any quakes unless we listen for months or years. But we may be able to do better on planets and moons that do not have air and wind. A lander on Jupiter's moon Europa, for example, could have a large chance of detecting events within a few days of recording even if the instrument is not put on the ground.

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“…This level of error at an epicentral distance of 20° would change ScS arrival time by ~10 seconds, impairing the use of this kind of data even with an accurate seismic model. However, the results of the Marsquake Service blind test (Clinton et al, 2017) suggest that many Martian events may be located to a much higher degree of accuracy (van Driel et al, 2019). The utility of ScS observations in determining core radius will be determined by the degree of structural complexity, the level and distribution of seismicity on Mars, and the amount of "noise" or unwanted signal present as ScS is recorded.…”

Section: Seismic Propertiesmentioning

confidence: 99%

Core formation and geophysical properties of Mars

Brennan

Fischer

Irving

2020

Earth and Planetary Science Letters

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The chemical and physical properties of the interiors of terrestrial planets are largely determined during their formation and differentiation. Modeling a planet's formation provides important insights into the properties of its core and mantle, and conversely, knowledge of those properties may constrain formational narratives. Here, we present a multi-stage model of Martian core formation in which we calculate core-mantle equilibration using parameterizations from high pressure-temperature metal-silicate partitioning experiments. We account for changing core-mantle boundary (CMB) conditions, composition-dependent partitioning, and partial equilibration of metal and silicate, and we evolve oxygen fugacity (fO2) self-consistently. The model successfully reproduces published meteorite-based estimates of most elemental abundances in the bulk silicate Mars, which can be used to estimate core formation conditions and core composition. This composition implies that the primordial material that formed Mars was significantly more oxidized (0.9-1.4 log units below the iron-wüstite buffer) than that of the Earth, and that core-mantle equilibration in Mars occurred at 42-60% of the evolving CMB pressure. On average, at least 84% of accreted metal and at least 40% of the mantle were This manuscript has been accepted for publication in Earth and Planetary Science Letters. 2 equilibrated in each impact, a significantly higher degree of metal equilibration than previously reported for the Earth. In agreement with previous studies, the modeled Martian core is rich in sulfur (18-19 wt%), with less than one weight percent O and negligible Si. We have used these core and mantle compositions to produce physical models of the presentday Martian interior and evaluate the sensitivity of core radius to crustal thickness, mantle temperature, core composition, core temperature, and density of the core alloy. Trade-offs in how these properties affect observable physical parameters like planetary mass, radius, moment of inertia, and tidal Love number k2 define a range of likely core radii: 1620-1870 km. Seismic velocity profiles for several combinations of model parameters have been used to predict seismic body-wave travel times and planetary normal mode frequencies. These results may be compared to forthcoming Martian seismic data to further constrain core formation conditions and geophysical properties.

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Preparing for InSight: An Invitation to Participate in a Blind Test for Martian Seismicity

Cited by 40 publications

References 51 publications

A Geophysical Perspective on the Bulk Composition of Mars

A Geophysical Perspective on the Bulk Composition of Mars

On‐Deck Seismology: Lessons from InSight for Future Planetary Seismology

Core formation and geophysical properties of Mars

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