Computing Path Effects of A Large Magnitude Event from Path Effects of Many Small Magnitude Events on The Same Rupture Plane

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

Submitted September 11, 2022, SCEC Contribution #12342, 2022 SCEC Annual Meeting Poster #235

The most promising way to improve the accuracy of hazard curve calculation is through the removal of the ergodic assumption. For example, wave propagation path effects between a source location and a site should be considered as repeatable, with their possible values constituting epistemic uncertainty. During most Ground Motion Models (GMM) development, 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 of the event. Since most earthquakes in empirical datasets have small magnitudes (M<5), such an assumption is reasonable because the ruptured plane is small. However, when the seismic hazards of future large magnitude earthquakes are considered, their path effects are assumed to be the same as for small magnitude events with the same path. 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 and could lead to inaccurate seismic hazard assessment. Theoretically, we would need to include an infinite number of paths spanning from the full area of the complex rupture plane when estimating the path effects of large magnitude earthquakes. In reality, we need to make simplifications, such as aggregating path effects from small magnitude earthquakes that cover the entire rupture plane.

While we initially used CyberShake simulations, the range of magnitudes and source-site combinations is not adequate to replicate what is observed empirically. We therefore 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. Then, we compare the mean path effects among different magnitude groups of events and examine any difference dependence on distance and azimuth. The work is on-going and we add simulations as-needed to test the stability of the initial results and to test various research hypotheses. Finally, based on our results, we plan to propose an universal relationship that helps researchers and engineers estimate accurate path effects of a large magnitude event from that of many smaller ones on the same rupture plane. At the SCEC meeting, we will present our preliminary results.

Meng, X., Goulet, C. A., & Graves, R. W. (2022, 09). Computing Path Effects of A Large Magnitude Event from Path Effects of Many Small Magnitude Events on The Same Rupture Plane. Poster Presentation at 2022 SCEC Annual Meeting.

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