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Open Access Publications from the University of California

Department of Earth, Planetary, and Space Sciences

There are 474 publications in this collection, published between 1992 and 2024.
Recent Works (474)

End-member models of boundary-modulated convective dynamos

Convective planetary dynamos depend upon secular cooling and internal radioactive decay for generating fluid motions within the core. Some planetary dynamo models also include heat flux variations along the core-mantle boundary (CMB) that modify the dynamo process. Here we study the effects of CMB heat flux variations in two sets of numerical dynamo models. In the first set, the possibility of dynamo action in a stably-stratified, Boussinesq, rotating spherical fluid shell is investigated. In these cases, lateral variations in CMB heat flux can drive significant zonal flows, but no dynamo action develops. In the second set of models, the fluid shell is neutrally-stratified. Dynamo action in these models is controlled by the pattern of CMB heat flux.Our neutrally-stratified models are relevant for studying the limiting effects of strong boundary forcing acting atop a convectively well-mixed state. We study four neutrally-stratified dynamo cases with different spherical harmonic heat flux patterns imposed on the CMB: Y10, Y11, Y20 and Y22. These cases demonstrate that the fundamental symmetries of the dynamo field follow the spatial symmetries of the CMB heat flux pattern. Our results show that convective dynamos are not necessarily killed by boundary-driven thermal winds, a result of interest if Earth's core top is close to adiabatic. A strong Y10 forcing is likely to produce a dynamo with hemispherical magnetic field structure reminiscent of Mars surface magnetization. However, as boundary-modulated convective dynamos produce magnetic fields generally one order of magnitude weaker than homogeneous convective dynamos with an equivalent forcing amplitude, it seems unlikely that this process is at the origin of Mars' regions of strong crustal magnetization. © 2011 Elsevier B.V.

Constraints on the martian crust away from the InSight landing site.

The most distant marsquake recorded so far by the InSight seismometer occurred at an epicentral distance of 146.3 ± 6.9o, close to the western end of Valles Marineris. On the seismogram of this event, we have identified seismic wave precursors, i.e., underside reflections off a subsurface discontinuity halfway between the marsquake and the instrument, which directly constrain the crustal structure away (about 4100-4500 km) from the InSight landing site. Here we show that the Martian crust at the bounce point between the lander and the marsquake is characterized by a discontinuity at about 20 km depth, similar to the second (deeper) intra-crustal interface seen beneath the InSight landing site. We propose that this 20-km interface, first discovered beneath the lander, is not a local geological structure but likely a regional or global feature, and is consistent with a transition from porous to non-porous Martian crustal materials.

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