CEE Seminar (ZOOM): Seismic Site Response in Sedimentary Basins

ZOOM Link will be distributed by the CEE Department
Chukwuebuka C. Nweke, Ph.D., E.I.T.

Assistant Professor
Sonny Astani Department of Civil and Environmental Engineering
Viterbi School of Engineering
University of Southern California

Abstract: Sedimentary basins are depressions in the earth’s surface that consist of alluvial deposits and sedimentary rocks, which are geologically younger and have slower seismic wave velocities than the underlying basement rock, and also decrease in thickness toward their margins. An important characteristic of the seismic response of these basins is that seismic waves are often trapped and reflected due to their interactions with the deep structure of sediments and the associated variations in material properties, per Snell’s Law, resulting in the generation of propagating surface waves in addition to the accompanying propagation of “body” waves. Such basin effects are known from first-principles to depend on a complex series of factors related to three-dimensional basin geometry (shape, depth, etc.) and aspects of the source-to-site path (i.e., the manner in which incident waves approach and enter the basin). These complexities are implicitly included in three-dimensional ground motion simulations, which can predict strong basin effects and are incorporated in a relatively simple manner in sediment depth-dependent components of semi-empirical ground motion models. Not surprisingly these two modeling frameworks provide different outcomes. We use non-ergodic estimates of site response, as observed from recordings, to investigate basin effects and the effectiveness of different modeling procedures for predicting such effects. We also investigate the site-to-site component of within-event variability for basin and non-basin sites, which is useful for hazard analyses. 

Bio: Chukwuebuka (Buka) Nweke is a professor of civil and environmental engineering at the University of Southern California, Viterbi School of Engineering. He directs the N.E.S.T Research Group where his research is focused on solving problems at the intersection of geotechnical engineering, earthquake engineering, seismology and geomorphology. Some of his investigation topics include: characterizing sedimentary basin effects in earthquake hazards, evaluation of physics-based earthquake simulations for the purposes of analyzing associated hazards and improving infrastructure resilience, and investigating the mechanical behavior (static and dynamic) of bio-cemented soils in order to establish sustainable alternatives for hazard mitigation. 

Professor Nweke earned his Ph.D. and M.S in civil (geotechnical) and environmental engineering at UC Berkeley, and his B.S in civil and environmental engineering at UC Davis. After completion of his graduate studies, Professor Nweke was an NSF-AGEP Postdoctoral Research Fellow in the civil and environmental engineering department at UCLA. Prior to his current position, he was a practicing engineering consultant for ENGEO, a geotechnical and environmental engineering firm.