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Constraining Large Magnitude Event Source and Path Effects Using Ground Motion Simulations

Description: 

The most promising way to improve Probabilistic Seismic Hazard Analysis is through the separation of epistemic and aleatory uncertainties. For example, wave propagation path effects between a source location and a site should be considered as repeatable, with their possible ranges constituting epistemic uncertainty. However, path effects represented by Ground Motion Models (GMMs) often include unmodeled source effects, such as radiation pattern and directivity, which may lead to bias in seismic hazard assessment. Moreover, the path effects from one event to one site are assigned to a single path between one point and a site, regardless of the magnitude and extent of the rupture. For a large magnitude earthquake, seismic waves can travel from any point along the rupture plane that extends hundreds of kilometers. Hence the single travel path assumption for large magnitude earthquakes is potentially flawed.

The purpose of this study is to use ground motion simulations to investigate how source and path effects for large magnitude events can be represented in non-ergodic GMMs. We simulate earthquakes occurring on a fault plane with a large range of magnitudes, and sites covering a large range of rupture distances and azimuths. We first develop a non-ergodic GMM, in which radiation pattern and directivity effects are modeled using existing relationships. Then, we compare the mean path effects among groups of events with different magnitudes and examine any differences in dependence on distance and azimuth using two approaches. The first approach only considers smaller events that have the same shortest path to a site as a co-located larger event, while the second approach considers all smaller events on the larger event fault plane regardless of source to site path length. The results indicate that it is difficult to satisfactorily approximate the path effects of larger events with that of smaller events using either approach. This finding complicates our ultimate goal of developing guidelines for how large magnitude ruptures can be adequately represented within non-ergodic GMMs.

Session: Physics-Based Ground Motion Modeling [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Xiaofeng

Student Presenter: No

Invited Presentation: 

Authors