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Virtual Faults for PSHA

Description: 

Seismic source-to-site distance metrics are the primary influences on ground motion amplitude models (GMMs) for probabilistic seismic hazard analysis (PSHA). For well-characterized crustal fault sources, 2-d surficial “line” sources have evolved into 3-d, often multi-segment planar features, with geometric uncertainties treated in a logic tree format. On the other hand, seismic activity in areal zones, where unidentified faults often comprise significant if not dominant contributions to the hazard, has been modeled as either uniformly distributed, or heterogeneously distributed based on spatial patterns of historic seismicity. A simple, commonly used method of distributing seismicity in an areal zone is to first create a grid of points within the boundaries of the area zone. Each point is then assigned a seismicity rate based on an independent analysis, scaled to the area the point represents. Crustal GMMs in use today generally use two distance metrics: “Rjb”, the nearest distance to the horizontal projection of the fault plane, and/or “Rrup”, the nearest distance to the fault plane. It was recognized that because earthquakes occur on 3-d planar structures, using a point as the source gave incorrect distance metrics. Attempts have therefore been made to adjust the point source distance to these two metrics. However, seismic source models (SSMs) have become more explicit as to the strikes, dips, and depth distributions of rectangular ruptures specified for a given zone. In addition, GMMs now include geometrically sensitive parameters such as hanging-wall and depth-to-top-of-rupture corrections. Therefore, modeling each rupture associated with a gridpoint as a planar rupture, in accordance with the SSM specifications, has become necessary. A method for doing so is presented, in the context of the CEUS-SSC source model for the central and eastern U.S.

Session: Opportunities and Challenges in Source Modeling for Seismic Hazard Analysis

Type: Oral

Date: 4/20/2023

Presentation Time: 10:30 AM (local time)

Presenting Author: Roland LaForge

Student Presenter: No

Invited Presentation: 

Authors