Seismological implications of a lithospheric low seismic velocity zone in Mars

Zheng, Yingcai; Nimmo, F.; Lay, Thorne

doi:10.1016/j.pepi.2014.10.004

Cited by 27 publications

(43 citation statements)

References 45 publications

(23 reference statements)

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“…The Martian temperature profile (the "aerotherm") was calculated based on an adiabat from the median CMB conditions of Rivoldini et al (2011) (~21 GPa and ~2000 K). These correspond to a mantle potential temperature of 1600 K, consistent with previous estimates (e.g., Nimmo and Faul, 2013;Zheng et al, 2015). The lithospheric thermal boundary layer was approximated as a layer of linearly increasing temperature that intersects the adiabat at ~200 km, the estimated base of the thermal boundary (e.g., Khan et al, 2018).…”

Section: Physical Structuresupporting

confidence: 82%

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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Section: Physical Structuresupporting

confidence: 82%

Core formation and geophysical properties of Mars

Brennan

Fischer

Irving

2020

Earth and Planetary Science Letters

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“…The effect of temperature on shear modulus relative to pressure inside Mars is stronger and therefore results in a shear wave velocity reduction with depth in the lithosphere. The effect of this on seismic wave propagation is discussed in detail by Zheng et al ().…”

Section: Resultsmentioning

confidence: 99%

“…Last, but not least, the predictions made here can ultimately be tested with the upcoming InSight mission that will perform the first in situ measurements of the interior of Mars through the acquisition of seismic, heat flow, and geodetic data: Analysis of the seismic data to be returned from the SEIS experiment (Lognonné et al, ) on InSight will rely on more “classical” global seismology techniques in the form of traveltime tables for various seismic phases, surface wave dispersion, receiver functions, normal modes, and waveforms (e.g., Okal & Anderson, ; Panning et al, ; Zheng et al, ). These data will shed light on the interior physical structure of crust, mantle, and core, including velocity gradients and dicontinuities associated with mineral phase transitions and/or chemical boundaries.…”

Section: Discussionmentioning

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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“…Phobos is too far from inducing a significant tidal-seismic resonance. However, when Phobos' orbit decays to about 1.97 (current orbit is about 2.77) times of the martian radius, topography induced tidal-seismic resonance will be able to cause an orbit decay, estimated about 10 42A / based on current martian topography and an approximate homogenous Mars model (P-wave velocity " = 7.4 / , S-wave velocity % = 3.6 / , density = 4000 / 1 to match a 0S2 period of about 2300 s (Zheng et al, 2015)). This rate is then comparable to the current orbital decay rate of Phobos, which is about 1.28 × 10 4F / (Bills et al, 2005).…”

Section: Discussionmentioning

confidence: 99%

“…We also consider the effect of Q, which captures the dissipation effect of the planet. Previous work showed that Q could cause tidal phase lag and was important in calculating the orbital decay of moon (Zharkov and Gudkova, 1997;e.g., Bills et al, 2005;Nimmo and Faul, 2013;Zheng et al, 2015). The planet topography can also play a role in the tidal-seismic resonance.…”

Section: Model Setupmentioning

confidence: 99%

Rapid falling of an orbiting moon to its parent planet due to tidal-seismic resonance

Tian

Zheng

2020

Planetary and Space Science

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Tidal force plays an important role in the evolution of the planet-moon system. The tidal force of a moon can excite seismic waves in the planet it is orbiting. A tidal-seismic resonance is expected when a tidal force frequency matches a free-oscillation frequency of the planet. Here we show that when the moon is close to the planet, the tidal-seismic resonance can cause large-amplitude seismic waves, which can change the shape of the planet and in turn exert a negative torque on the moon to cause it to fall rapidly toward the planet. We postulate that the tidal-seismic resonance may be an important mechanism which can accelerate planet accretion process. On the other hand, tidal-seismic resonance effect can also be used to interrogate planet interior by long term tracking of the orbital change of the moon.

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Seismological implications of a lithospheric low seismic velocity zone in Mars

Cited by 27 publications

References 45 publications

Core formation and geophysical properties of Mars

Core formation and geophysical properties of Mars

A Geophysical Perspective on the Bulk Composition of Mars

Rapid falling of an orbiting moon to its parent planet due to tidal-seismic resonance

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