My research interests bridge the interface between geophysics and the engineering disciplines, primarily as a field-oriented experimentalist focused on earthquake hazards in general, and near-surface geophysics, neotectonics (active-fault assessment), and ground-motion site response in particular. This research has been largely concentrated in the North American Midcontinent (i.e., New Madrid seismic zone and Wabash Valley seismic zone), but also pursued in more than a half-dozen field campaigns conducted along the northern edge of the Tibetan Plateau in western China (TibetanPlateau_Seismic.JPG ). More recently, similar research projects have focused in the western U.S., including the Mojave Desert (DeathValley_Source.jpg; DeathValley_Seismograph.jpg), Eastern High Sierras of California, and Teton Range in Wyoming.

A significant part of the work has been devoted to the spatial and temporal evaluation of “blind” faults and other near surface neotectonic manifestations using geophysical imaging techniques. Research projects have integrated high-resolution seismic reflection (frequently using the horizontally polarized shear-wave mode), electrical resistivity, and ground-penetrating-radar with selective drilling to constrain subsurface complexities. My earliest work was the first in the United States showing horizontally polarized shear-waves (SH-mode) can be more amenable for imaging geologic features in low-strength, water-saturated, near-surface (< 100 m) sediment than the conventional P-wave methods. The SH-wave reflection technique has also proven effective for imaging the internal structural detail and geological foundation conditions of earth-fill embankment dams, as well as detecting minute flaws overlooked in their design and construction. We have shown the SH-wave method can cost effectively provide the required subsurface definition needed for remedial engineering of these high-hazard flood-control structures. In addition to imaging capability, we have used multi-component S-wave reflection energy to measure shear-wave splitting (i.e., birefringence) phenomena in fault deformed unlithified sediment lacking a surface manifestation. The phenomena gives rise to dynamic misties when resolved and corrected to a natural coordinate system, providing a measure of azimuthal anisotropy that can be used to define an anomalous inclusion orientation (e.g., fault strike, stress orientation, sedimentation fabric, among others). This technique can also be very helpful for seismc mapping of subsurface features in locations having limited accessibility (i.e., urban environments), where acquisition of traditional gridded surveys are unavailable.

The Chinese Earthquake Administration (CEA) became interested in these near-surface techniques in the early 2000's as part of their burgeoning national seismic hazard evaluation, where locating “capable” faults were proving similarly problematic, particularly in their vast urban areas. Collaborative field tests, supported by the Gansu provincial government and the central CEA, proved highly successful in identifying active faults in various locations across the Gansu and Qinghai provinces.

Other research interests include the influence thick soil/sediment deposits in the Mississippi and Wabash river valleys have on earthquake ground-motion characteristics. Specifically, how the local geology can alter (±) the amplitude, duration, and frequency content of an earthquake time series. The complex geometry and vertical/lateral variations within these regional deposits make estimating the ground motions of earthquake engineering interest problematic, however. To address these issues, we collect in situ field measurements of the primary dynamic soil properties responsible for the effects and use the results to numerically model ground motions for scenario events. To help evaluate the validity of the calculated transfer functions, the University of Kentucky operates and maintains the Kentucky Seismic and Strong Motion Network (KSSMN), operated by the Kentucky Geological Survey and assisted by my lab in the Department of Earth and Environmental Sciences. The network currently consists of 22 permanent seismic and strong-motion stations and eight temporary seismic stations. Historically, the network was focused on the New Madrid seismic zone but has recently deployed a relatively dense temporary array in eastern Kentucky to characterize microseismicty where there is a potential for inducing earthquakes from wastewater injection associated with hydrocarbon production. More information is available at: https://www.uky.edu/KGS/earthquake/