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Complex Rayleigh Wave Effects on the Seismic Demands of Mid-Rise Buildings

Jorge A. Castillo Castellanos, Monica D. Kohler, Anthony T. Massari, & Robert W. Clayton

Published August 15, 2017, SCEC Contribution #7699, 2017 SCEC Annual Meeting Poster #085

Observations of earthquake motions recorded by spatially dense seismic arrays in buildings located in the northern Los Angeles basin suggest the presence of complex, amplified surface wave effects on the seismic demand of mid-rise buildings. Several moderate earthquakes produced large-amplitude, seismic energy with slow shear-wave velocities that cannot be explained or accurately modeled by the SCEC community seismic velocity model or by Vs30 values. In this study, we examine the effects of different sedimentary basin geometries on the nonlinear response of a mid-rise structural model based on an existing, instrumented building. Using two-dimensional finite-difference predictive modeling, we show that when an earthquake focal depth is near the vertical edge of an elongated and relatively shallow sedimentary basin, dramatically amplified and complex surface waves are generated as a result of the waveguide effect introduced by this velocity structure. In addition, for certain source-receiver distances and basin geometries, body waves convert to secondary Rayleigh waves that propagate both at the free-surface interface and along the depth interface of the basin that show up as multiple large-amplitude arrivals. The predicted ground motions for the different basin geometries are then combined with high-fidelity nonlinear finite-element models of an existing, instrumented, 15-story steel moment-frame building to test its nonlinear response and associated damage at its resonant frequencies. This study aims to provide quantitative insight into the causative relationship between a sedimentary basin shape and the generation of Rayleigh waves at depth, surface waves at the free surface, scattered seismic energy, and the sensitivity of building responses to each of these. The results contribute to identifying the potential detrimental basin effects on seismic response of civil infrastructure, and will guide future efforts on how to include basin effects in the next generation of seismic design guidelines.

Castillo Castellanos, J. A., Kohler, M. D., Massari, A. T., & Clayton, R. W. (2017, 08). Complex Rayleigh Wave Effects on the Seismic Demands of Mid-Rise Buildings. Poster Presentation at 2017 SCEC Annual Meeting.

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