Overview
My interests lie in the fields of earthquake seismology, applied geophysics, wave propagation, fluid dynamics, and digital-data processing.
In seismology, I am interested in various aspects of earthquake ground motions, such as simulation of radiation from fault ruptures (Pure and Applied Geophysics, 2017) or studies of amplification of seismic waves by sedimentary layers. My research also involves earthquake physics in general (Bulletin of the Seismological Society of America, 2022; Bulletin of the Seismological Society of America, 2022). I am looking into the factors responsible for the high-frequency radiation from earthquakes (Journal of Seismology, 2017; Pure and Applied Geophysics, 2021; Bulletin of the Seismological Society of America, 2023) and generation of extreme earthquake shaking (Journal of Seismology, 2021; Journal of Earthquake Engineering, 2022). Another topic of long-term interest is uncertainty in seismological inversions for the distribution of slip on faults of major earthquakes (Pure and Applied Geophysics, 2023). Working with digital seismic data involves a great deal of computer programming, in which I often rely on myself, since many non-traditional data-processing tasks do not leave other choice. I co-authored the computer code FINSIM (in collaboration with Dr. Gail Atkinson), which calculates seismic radiation from rupturing faults and is currently used in over 170 institutions in 36 countries. My interests also include nonlinear elasticity of earth materials and observation and modeling of nonlinear effects in seismic-wave propagation.
Read a news story on the latest research on predicting ground shaking from future very large earthquakes.
I study the effects of seismic waves and vibrations on the flow and mobilization of entrapped organic fluids (such as oil, gas, or organic contaminants) in geologic formations. This research aims at developing field technologies of enhanced petroleum recovery or groundwater remediation using seismic and acoustic stimulation. We are focusing on the fundamental aspects of fluid dynamics of immiscible two-phase flow in the presence of vibrations, with the intent to elucidate the mechanisms by which the vibrations mobilize the non-wetting fluids (related articles: Geophysics, 1994; Geophysical Research Letters, 2005; Geophysics, 2006; Geophysics, 2010; Geophysical Research Letters, 2011).
A related subject is the capillary instability that causes the break-up of non-wetting fluids into droplets in porous channels (see: Transport in Porous Media, 2009; Physics of Fluids, 2010; Physics of Fluids, 2011). To describe the break-up correctly, we also study the thickness of wetting films left on pore walls during liquid-liquid invasion (see: Physical Review E, 2011).
Another area of my research that is closely relevant is the elastic-wave propagation in porous solids saturated with two fluids (e. g., oil and water). A model for the wave velocity in such a medium was presented in Geophysics, 2014. I also looked into the meaning of tortuosity, the fundamental uncertainty in its measurement, and the limitations that its unpredictability imposes on the ability of the classic theory by Biot to describe waves in saturated rocks (see: Pure and Applied Geophysics, 2016).
My applied-geophysics agenda revolves around using multichannel-seismic, multi-electrode electrical-resistivity, and ground-penetrating radar (GPR) systems for shallow-subsurface exploration. Examples of work include prospecting for new sand-and-gravel deposits (related article: Journal of Applied Geophysics, 2002) or GPR applications to the assessment of road quality (Nondestructive Testing and Evaluation, 2016). I have also long been interested in the physics of seismic radiation from Vibroseis sources (see project description below).
Current and Recent Sponsored Projects
Sonic stimulation of reservoirs and aquifers
Since 2002, this subject has been supported by awards from the National Science Foundation, Petroleum Research Fund, and Department of Energy.
All projects have a common goal of developing the physical foundations of the technologies of sonic stimulation of reservoirs and aquifers. We focus on the basic capillary physics explaining the pore-scale mechanism of fluid mobilization in rock by seismic waves and vibrations, through theoretical and laboratory studies. The studies have been performed by our multidisciplinary team of scientists from the Department of Geological & Atmospheric Sciences and Department of Chemical & Biological Engineering. The theoretical and numerical modeling is primarily conducted by me and my students at the Department of Geological & Atmospheric Sciences. The laboratory work uses the techniques of visualization of fluid-flow in porous volumes allowing direct observation of pore-scale effects produced by vibrations. The experiments are carried out by my partner Dr. Dennis Vigil and our joint students at the Department of Chemical & Biological Engineering.
Applied geophysics
2002-2010 "Source signature of surface vibrators". Sponsors: WesternGeco, ConocoPhillips.
This industry-sponsored research has looked into improving the quality of deep seismic imaging in oil exploration through better understanding of the Vibroseis source. Seismic vibrators are the most common source of seismic energy in land exploration; however, the physics of Vibroseis radiation is not satisfactorily understood. For example, we have worked on the subjects of how ground nonlinearity around the vibrating plate and non-rigidity (flexing) of the plate affected the outgoing waves (see: Geophysics, 2004; Geophysical Prospecting, 2005; Geophysics, 2006; Journal of Sound and Vibration, 2012). I am currently exploring the correct representation of the source signature of the Vibroseis source as seen at depth.
Graduate Students
Elizabeth Sunday (Ph.D.) studies how the choices of fault-slip distribution, temporal shape of slip, and speed at which ruptures travel create an uncertainty in the predictions of ground shaking from future earthquakes.
Geophysical Equipment Resources
With our state-of-the-art equipment, we are capable of conducting precise geophysical surveys. My geophysics lab is equipped with a Geometrics StrataView 24-channel engineering seismograph, ideal for detailed seismic-refraction and reflection studies. The lab also includes a Noggin 250/500 MHz ground-penetrating radar, providing unique possibilities for high-resolution subsurface imaging.