Application of Directivity in PSHA and the Effect of Centering

Date: 4/25/2019

Time: 10:45 AM

Room: Pine

The PEER Working Group report on Ground Motion Directivity Modeling for Seismic Hazard Applications is expected to be released early this year. This multi-year effort aims to provide recommendations for incorporating directivity effects from models developed during the NGA-West2 project into probabilistic seismic hazard analyses. The modeling of directivity is a complex problem due to the limited data available from large magnitude and near fault data, and the development of the majority of the models only after the ground motion models have been completed, instead of incorporated within them.

While the draft Ground Motion Directivity Modeling for Seismic Hazard Applications recommendations find that all of the directivity models considered are suitable for application to capture the effects of directivity, not all of the models are centered, as they were originally developed to be included in a ground motion prediction equation. The impact of centering on the directivity effect can be large and have a significant impact on the results of the probabilistic seismic hazard analysis.

Example seismic hazard analyses are performed in the Bay Area and Los Angeles to demonstrate the effect of the individual directivity models recommended in the draft report. The draft recommendations from the PEER report were implemented as a suite of directivity models to demonstrate the effect of the recommendations.

Additionally, to examine the effect of centering, a model was developed to center each of the directivity models and was then applied accordingly. To demonstrate the impact of centering on individual earthquakes, scenarios are presented and the change in the mean ground motion due to centering is shown. The example analyses are then rerun with the newly centered models to demonstrate the cumulative effect on probabilistic seismic hazard analyses. Recommendations are provided in the near term for centering models, and incorporating directivity parameters into ground motion models directly in the long term.

Presenting Author: Jennie Watson-Lamprey

Authors