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

Xiaofeng Meng, Robert W. Graves, & Christine A. Goulet

Submitted September 10, 2023, SCEC Contribution #12814, 2023 SCEC Annual Meeting Poster #172

The most promising way to improve the accuracy of hazard curve calculation is through the separation of epistemic and aleatory uncertainties. For example, wave propagation path effects should be considered as repeatable, with their possible variability 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 an event to a site are often represented by a single path between one point on the fault and the site, regardless of the magnitude and extent of the rupture. For a large magnitude earthquake, seismic waves 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. Theoretically, we need to include an infinite number of paths from the entire rupture plane when estimating the path effects of large magnitude earthquakes. In reality, we may make simplifications, such as aggregating path effects from small magnitude earthquakes that sample the larger rupture plane.

The purpose of this study is to use ground motion simulations to investigate ways in which source and path effects for large magnitude events can be represented in non-ergodic GMMs. We designed a new ground motion simulation study, which includes 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 different magnitude groups of events and examine any difference dependence on distance and azimuth. Our ultimate goal is to develop guidelines for how large magnitude ruptures can be adequately represented within non-ergodic GMMs.

Meng, X., Graves, R. W., & Goulet, C. A. (2023, 09). Constraining Large Magnitude Earthquake Source and Path Effects Using Ground Motion Simulations. Poster Presentation at 2023 SCEC Annual Meeting.

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