UC San Diego

High-frequency (here defined for a maximum frequency (f_max) larger than about 1 Hz) ground motions are closely relevant to building response associated with small structures of engineering interests. Gaining a deeper understanding of the propagation of high-frequency seismic waves and characteristics of the resulting ground motions is therefore a principal goal for seismologists and earthquake engineers. Earthquake simulations, in particular those based on physics-based and deterministic models, have drawn significant attention from the seismic community in the most recent decades as a valuable supplement to recorded data. With the potential ability to accurately characterize broadband wavefields, numerical simulations have their own limitations, in particular difficulty in characterizing the underlying physical parameters to a sufficient resolution and computationally accommodating regional-scale models for seismic hazard analysis. The primary objective of this dissertations is to explore and rate the effects on high-frequency ground motions from various model features, which sheds light on their individual and mixed contributions and importance for future modelers. Chapter 1 is an introduction, providing background and motivation for each of the following chapters. Chapters 2 and 3 focus on model characteristics that govern the high-frequency ground motions. Chapter 2 proposes a calibration approach that enhances the near-surface velocity structure that is insufficiently resolved in community velocity models. In Chapter 3, we simulate a series of models to investigate the effects of topography, small-scale heterogeneities, frequency-dependent attenuation, and low near-surface velocities on the resulting wavefields and ground motions as the frequency extends up to 5 Hz. In Chapter 4, we propose a method to incorporate surface topography in constraining the 3D subsurface structure to predict site response. Chapter 5 studies nonlinear effects using dynamic simulations and proposes an equivalent kinematic source generator to emulate near-source plasticity in terms of the resulting peak ground velocities and spectral accelerations.