Many natural hazards have been well known and qualitatively understood for decades, but still lack accurate measures of how damaging future events will be. For example, despite many years of research, it still remains a question as to how much variability in ground motions one should expect of a large San Andreas type earthquake, and whether early warning for debris flows can be successfully implemented. In this talk, I address both of these questions by using simple but physically sound mechanical principles to quantify certain aspects of these hazards.
The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle upwellings, sinking of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Modeling the long-wavelength dynamic geoid allows us to constrain the radial viscosity profile of the mantle. I will discuss new solutions for the mantle viscosity structure and its uncertainty based on a suite of joint whole-mantle tomographic models of both S- and P-wave velocity as well as density. The resulting density variations in the lowermost mantle span scenarios in which the net buoyancy of the Large Low Shear Velocity Provinces (LLSVPs) appears to be primarily controlled by temperature, as well as those in which the LLSVPs represent intrinsically dense material. Finally, I will show results from kinematically-constrained mantle convection models with idealized viscosity profiles and make a comparison between emergent large-scale structures and structures observed in seismic tomography.
In tectonically active landscapes, both tectonically driven base level changes and bedrock damage can influence the spatial and temporal patterns of erosion. Though the influence of base level changes from differential rock uplift rates on erosion has been examined extensively in previous studies, few studies have examined whether the tectonic influence on bedrock damage may influence landscape evolution. In this talk, I show how tectonic stress interacts with topography and influences landscape evolution by altering the rates and patterns of bedrock fracturing, weathering, and erosion. First, I show how the present-day topographic stress fields influence bedrock fracture patterns in Forsmark, Sweden. The population of existing fractures likely reflects stress history, but the present-day topographic stress field influences the relative abundance of open fractures near the surface and at depths of hundreds of meters. Second, I present my group’s work in the eastern Tibet, which shows that the tectonic control on bedrock damage may explain the measured changes in rock erodibility and landslide characteristics.
University of Hawaii
Geoscientists have long recognized the importance of generating extreme pressures and temperatures to reproduce in laboratory settings the conditions present in planetary interiors. Such experiments provide the basis for understanding the nature and mechanisms of dynamic processes taking place within deep interiors of Earth and other planetary bodies. Since early 1960s, mineral physics has rapidly emerged and been recognized as an important interdisciplinary field in Earth sciences, providing an essential link between laboratory measurements of the physical and chemical properties of minerals and rocks under extreme conditions and the geophysical and geochemical observations of the Earth’s interiors. Advanced high-pressure and synchrotron X-ray techniques have permitted experimental mineral physicists to probe the micro-scale properties of planetary materials that govern macro-scale behaviors of the complex planetary systems. Here, I will briefly describe the past, present, and future of the field, followed by recent research on the viscoelastic properties of iron-carbon liquids, elastic and thermal transport properties of high-pressure ices, and the implications on the internal structure and dynamics of planetary interiors.
California Institute of Technology
The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally-driven disruption may be an important process in the removal of rocky bodies in the Solar System. On a separate front, transit observation of various planetary systems indicates that near-star disruption of small planetesimals is common in the Galaxy, prompting the need to understand such a process using our own Solar System as an example. Here I will discuss how the debris streams arise from possible thermally-driven disruptions in the near-Sun region based on simulations of the disruption of near-Sun asteroids, and how can we use meteor data to understand the asteroid disruptions near the Sun. I will show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. Finally, I will briefly discuss the implication of our finding for exoplanetary systems.