Seismo Lab Brown Bag Seminar

Seismic community velocity models (CVMs) are foundational for many basic and applied topics ranging from derivations of earthquake source properties to simulations of ground motions. CVM accuracy directly impacts the epistemic uncertainty of simulated wave fields generated by earthquakes or 3D physics-based simulations. We present an innovative methodology applied to the Northern California CVM, to evaluate the epistemic uncertainty reflected in key intensity measures of ground motions related to seismic hazard analysis. The evaluation employs three-dimensional physics-based ground motion simulations of a set of local small earthquakes with magnitudes ranging from 3.5 to 4.5, which then are compared to recorded data. Evaluation of differences between recorded and simulated data in spectral amplitude, phase matching, and waveforms' duration allows us to estimate epistemic uncertainties and identify features and subregions of the CVM that need refinements. Using small events and the point source approximation facilitates a focus on properties of the CVM rather than finite source ruptures. Thus, the misfit between recorded and simulated waveforms can be mainly attributed to structural complexities not fully represented in the examined CVMs and, to a lesser extent, the source parameterization. Finally, we discuss the challenges in modeling this kind of earthquake, especially in decoupling the sources of epistemic uncertainty and systematic misfits between recorded and simulated data, which transduces in the potential mapping of mismodeled source effects into wave propagation effects.