• Our research interests have been primarily in understanding the physical processes that control the evolution of terrestrial planets (Earth, Moon, Mars, ...). Modern space exploration has provided high resolution gravity and topography data about many planets. Other observational techniques including seismology and in-situ sampling have revealed the structure and composition of planetary interiors (primarily for Earth and its Moon, but soon for Mars as well). Understanding the physical processes that are responsible for these observations and how they are related to thermal evolution of planets is our primary goal of research. Because the planetary dynamics depend on how a planet responds to forces (i.e., a material property called the rheology), another major aspect of our research is to understand the rheological properties of Earth's materials.
  
  Thermal convection in planetary mantles is the most important physical process that controls the dynamics of terrestrial planets. Mantle convection determines the thermal structure in the mantle that has been revealed in seismic images, controls the distribution of heat release at the surface (volcanoes and seafloor spreading) and surface topography (mountain ranges and ocean basins), dictates the large-sclae horizontal movement of surface crust (i.e., plate tectonics for Earth), and ultimately governs the thermal evolution of planets (from shortly after their formation to ...). To study the dynamics of mantle convection and its surface manifestation, we use both instability analyses and numerical simulation in our research. Recently, building upon our previous studies on global mantle flow, we have focused our effort on understanding interaction of convection at multiple scales, i.e., the global scale associate with plate motion and the small-scale associated with thermal plumes. This problem has important implications to the heat transfer within the mantle and the style of mantle convection. We work closely with our global seismology group at CU (Mike Ritzwoller) to understand the seismic images of the mantle from the viewpoint of mantle dynamics.
  
  Another ongoing project is to understand the mantle rheology by examining the vertical motion of Earth's surface. In collaborating with Watts (Oxford), we have inferred the activation energy, one of the most important deformational properties for mantle materials, by using the observed flexural rigidity near seamounts. While we continue to make progress on this project, we recently started to study another closely related important problem on mantle rheology -- the influence of inhomogeneous mantle rheological structure on the vertical motion of Earth's surface since the last deglaciation (collaborating with John Wahr at CU).
  
  Our research on other terrestrial planets at the moment is primarily on understanding the long-wavelength topography and gravity on the Mars and their implications for thermal evolution of the Mars. In particular, we are interested in the mechanisms responsible for the formation of the crustal dichotomy and Tharsis rise (a volcanoic province occupying 1/4 of Mars surface). In addition to studies on the Mars, we continue our studies on the lunar evolution (with Marc Parmentier of Brown Univ.).



• I also have strong interests in high performance computing and numerical analysis. In working with scientists at Caltech (Gurnis) and CSIRO of Australia (Moresi), I have developed 3D full multigrid spherical finite element models of mantle (see an example of how a planet is cut to fit to parallel computers. Here is for multigrid ). With funding from NSF and CU, we have built a mid-sized PC-cluster (48 Pentium III processors with 48 Gbytes RAM) to run our applications. We also have access to parallel supercomputers at NSF supercomputer centers (through NPACI).



• Our research is supported by the NSF, NASA, and David and Lucile Packard Foundation.

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