Use of Non-Ergodic Ground-Motion Models for the National Hazard Maps
Session: Forthcoming Updates of the USGS NSHMs: Hawaii, Conterminous U.S. and Alaska
Type: Oral
Date: 4/28/2020
Time: 04:30 PM
Room: 230 + 235
Description:
The current national seismic hazard maps (NSHM) are based on ergodic ground-motion models (GMMs) for SA for broad regions. As ground-motion data sets have grown, large differences between the observed SA and the ergodic GMMs can be seen for specific site/event pairs on the scale of 10km. Systematic effects at even shorter length scales are seen in 3-D numerical simulations. Accounting for the spatial differences by using non-ergodic GMM reduces the sigma of the GMM by about 40% for all sites and changes the median (higher or lower) for each site/source pair. Trial applications of nonergodic GMMs to California show that the 2500-yr return period ground motion can increase or decrease by a factor of 2 compared to the ergodic GMM results. The move to non-ergodic GMMs is expected to lead to the largest changes in the estimates of the seismic hazard since the inclusion of the aleatory variability of the ground motion in the 1980s.
In the short-term, the non-ergodic GMMs can be used to define epistemic uncertainty ranges about the ergodic GMMs to show the range of potential changes to the hazard. This framework can also be used for incorporating 3-D basin effects from simulations. In the long-term, changes to the PSHA software used by the USGS are needed to implement non-ergodic GMMs. First, the coordinates of the source and the site need to be provided to the GMM subroutine in addition to M,R,etc. Second, capturing the epistemic uncertainty in the non-ergodic terms for each source/site pair requires 100s of GMMs to be used on the logic tree. This is not practical for computing NSHMs sampling each branch The PSHA program will need more efficient methods to sample the epistemic uncertainty in the non-ergodic GMM. Currently, GEM is making modifications to the OpenQuake PSHA program to use non-ergodic GMMs with polynomial chaos for efficient calculation speed. These methods are incorporated into HAZ45. The results from these two PSHA programs can be used for QA to test the implementation of non-ergodic GMMs in the USGS software.
Presenting Author: Norman A. Abrahamson
Authors
Norman A Abrahamson abrahamson@berkeley.edu University of California, Berkeley, Berkeley, California, United States Presenting Author
Corresponding Author
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Linda Al Atik linda.alatik@gmail.com Linda Alatik Consulting, San Francisco, California, United States |
Yousef Bozorgnia yousef.bozorgnia@ucla.edu University of California, Los Angeles, Los Angeles, California, United States |
Chih-Hsuan Sung karensung@berkeley.edu University of California, Berkeley, Berkeley, California, United States |
Christine A Goulet cgoulet@usc.edu Southern California Earthquake Center, Los Angeles, California, United States |
Nicholas Gregor nick@ngregor.com Nicholas Gregor Consulting, Oakland, California, United States |
Albert R Kottke arkk@pge.com Pacific Gas and Electric Company, San Francisco, California, United States |
Nicolas M Kuehn kuehn@g.ucla.edu University of California, Los Angeles, Los Angeles, California, United States |
Maxime Lacour maxlacour@berkeley.edu University of California, Berkeley, Berkeley, California, United States |
Grigorios Lavrentiadis glavrent@berkeley.edu University of California, Berkeley, Berkeley, California, United States |
Chenying Liu cliu662@gatech.edu Georgia Institute of Technology, Atlanta, Georgia, United States |
Jogre Macedo jorge.macedo@gatech.edu Georgia Institute of Technology, Atlanta, California, United States |
Xiaofeng Meng xiaofenm@usc.edu University of Southern California, Los Angeles, California, United States |
Sebastian von Specht sspecht@uni-potsdam.de University of Potsdam, Potsdam, , Germany |
Melanie Walling mwalling@geoengineers.com GeoEngineers Inc., Seattle, Washington, United States |
Kathryn E Wooddell kxwl@pge.com Pacific Gas and Electric Company, San Francisco, California, United States |
Use of Non-Ergodic Ground-Motion Models for the National Hazard Maps
Category
Forthcoming Updates of the USGS NSHMs: Hawaii, Conterminous U.S. and Alaska