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Eric Dunham, Stanford University
Earthquake rupture simulations provide several practical outputs, including predictions of strong ground motions for use in seismic hazard assessments and, for offshore earthquakes, predictions of tsunami excitation. I will review how these simulations are done and what inputs are required. For example, generating realistically complex ruptures for high frequency ground motions requires incorporating small-scale details of fault surface roughness, which can be inferred, at least in a statistical sense, from geological observations. Similarly, megathrust rupture simulations require accurate structural models, particularly near the trench. But another key ingredient, the initial stress on the fault just prior to rupture, is rather poorly constrained. Those stresses arise from tectonic loading and the past history of slip, motivating simulations over vastly longer (~10-10,000 year) time scales. Here the link to geodynamics becomes clear. I will provide several examples of how longer-term loading and deformation processes influence earthquake behavior, drawing from earthquake cycle simulations in viscoelastic and poroelastic media. The former is motivated by questions regarding the depth extent of large ruptures and the possibility of coseismic slip penetration into nominally ductile parts of the lower crust, while the latter models focus on induced seismicity. I will close with a vision for thermomechanical earthquake cycle models, a fascinating but challenging problem that I believe the CIG community is well poised to tackle.
Peter Driscoll, DTM Carnegie
Simulations of planetary evolution typically rely on simplified physics in order to model the relevant Gyr time-scales. Simplified, or “parameterized”, physics are necessary because full 3D first principles simulations are often too computationally expensive to readily produce Gyr long models. Here we present recent planetary evolution models of the thermal and magnetic histories of Earth and Venus, highlighting the influence of magmatic cooling on the maintenance of a core dynamo. We also demonstrate the discrepancy between magnetic field behavior predicted by a terrestrial thermal history applied to dynamo scaling laws and the same history applied 3D dynamo models. These 3D dynamo evolution models offer a unique prediction for the paleomagnetic signature of inner core nucleation, that may be supported by some anomalous paleogeographic motions in the Neoproterozoic. Finally, we show predictions for the thermal and orbital evolution of gravitationally interacting exoplanets using parameterized tidal dissipation models, which could have implications for planetary habitability around low mass stars.
Moritz Heimpel, University of Alberta; Nick Featherstone, CU Boulder; and Jonathan Aurnou, UCLA
Planetary jet streams and vortices have been studied for over 350 years, yet their origin and dynamics are still vigorously debated. On both Jupiter and Saturn zonal flow consists of equatorial superrotation and alternating East-West jets at higher latitude. On Jupiter, numerous vortices, the vast majority anticyclones, occur with various sizes and lifetimes, interacting strongly with the zonal flow. Saturn's vortices and jets are also clearly coupled, and its North and South polar vortices are cyclonic.
We have used the anelastic dynamo codes Magic and Rayleigh in non-magnetic mode to study rotating convection in 3D spherical shells. The models include a polytropic, ideal gas equation of state, and are driven by convection at depth but grade to a stably stratified, low density shallow layer. In model simulations convective plumes rising from the deep interior impinge on the stably stratified layer, diverge near the outer spherical surface, and efficiently create the dominant anticyclones, which are shielded by downwelling cyclonic rings and filaments. These results may explain the dominance of anticyclones and the flow structure of small and medium sized anticyclonic ovals on Jupiter. The largest of our model vortices form in westward anticyclonic shear nearest the equatorial jet, similar to Saturn’s "storm alley" and Jupiter’s Great Red Spot.
Georg Stadler, New York University
For many problems in Geophysics, we now have available well-established governing equations and efficient solvers. The systematic integration of these models with various observational data---the inverse problem---has the potential to lead to new insights and understanding of fundamental processes in Geophysics. I will discuss computational and theoretical challenges arising indeterministic and probabilistic approaches to inverse problems. Examples from inverse mantle convection, inverse ice dynamics and seismic imaging will be used for illustration purposes.