My research activities range from experimental seismology to the physics of finite-frequency seismic wave propagation in inhomogeneous media, both elastic and inelastic. The former pertains to the development and application of novel experimental techniques for determining the physical properties of the Earth's crust and mantle, and for shedding light on the source attributes of earthquakes and underground explosions. The latter is concerned with the non-asymptotic, non-Snell's law behaviors of finite-frequency seismic wave propagation in complex media, such as frequency-dependent wave reflections from gradient zones, frequency-dependent wave-front, elastic body-wave dispersion, and the spatial continuity across a seismic "caustic". The exact mathematical descriptions of the finite-frequency wave propagation, derivable from the first principles, overcome fundamental shortcomings of the asymptotic ray theory (ART) and ray-summation based methods of wave-field computation. The new development enables the modeling of a host of naturally occurring scattering phenomena in wave media containing strong velocity gradients, making it possible to illuminate, among others, structural details within oil-bearing sedimentary basins and in transition zones of exceptional import, such as the uppermost part of the mantle lid.

My past research includes the analysis of broadband recordings to study the crust/mantle structures beneath the North American and Eurasian continents, intra-plate earthquake source scaling, the spatial attenuation of regional and teleseismic waves, seismic network calibration, frequency-dependent propagation of regional phases, and temporal changes in fault-zone attenuation following a major earthquake. I have also carried out research in forensic seismology whose objective is to strengthen the scientific and technical capabilities of verifying the compliance by state signatories with a Comprehensive Nuclear Test Ban Treaty. My immediate interest is in understanding the dynamical processes endemic to continental collision, assemblage and evolution using 2-D and 3-D tomographic imageries as a potent tool to gain knowledge on the depth structures beneath target regions.