A major focus involves “subduction zones”, the linear belts on Earth where tectonic plates converge, and one plate sinks into the mantle beneath the other plate. Earth’s largest earthquakes and volcanoes tend to occur at convergent boundaries. Research in Gao's Group focuses on understanding the nature of variation within and along subduction zones.  To address these questions, a variety of new and powerful seismological methods, including full-wave simulation and seismic tomography, teleseismic receiver functions, and seismic anisotropy, have been developed and implemented to image the crust and upper mantle structure with high resolution. Full-wave propagation simulation within the 3D Earth structures relies on high-performance computation, which is carried out at the Massachusetts Green High-Performance Computing Center.