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Implementing Rupture Directivity Effects Into PSHA

Description: 

The effects of rupture directivity on near-fault ground motions are known to be significant and should be included to accurately estimate the hazard, especially for long-period ground motions (Abrahamson, 2000). However, these effects are not explicitly accounted for in typical ground motions models, and therefore not in typical probabilistic seismic hazard analyses (PSHAs) because substantial confusion exists in practice about which directivity models to use and how to apply them to the median and aleatory variability of GMMs, especially to complex multi-segment rupture models (Donahue et al., 2019). In the response spectral approach, which we adopt, rupture directivity effects are considered by including adjustment factors to the elastic acceleration response spectrum at 5% damping. This approach lends itself readily to inclusion into PSHA (Rodriguez-Marek and Cofer, 2009).

This work describes an update to our 2020 rupture directivity model (Bayless et al., 2020), including formalized instructions for adjustments to the median and aleatory variability of the ground motion model to which it is applied. Additionally, we provide guidance on implementation, including deterministic and probabilistic applications, and methods for modeling hypocenter locations and multi-segment ruptures. The result is a comprehensive model suitable for use in future PSHAs, including those performed as part of the USGS National Seismic Hazard Model. The model applies to strike-slip earthquakes only. A future update will address directivity effects for other styles of faulting.

Session: The 2023 USGS National Seismic Hazard Model and Beyond [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Jeff

Student Presenter: No

Invited Presentation: 

Authors