SCEC Award Number 22154 View PDF
Proposal Category Workshop Proposal
Proposal Title Workshop on evaluation of seismic hazard models with fragile geologic features
Name Organization
Mark Stirling University of Otago (New Zealand) Michael Oskin University of California, Davis
Other Participants
SCEC Priorities 4b, 5b, 5d SCEC Groups Geology, GM, EFP
Report Due Date 10/11/2022 Date Report Submitted 10/11/2022
Project Abstract
In the last year, fragile geologic features (FGFs) studies have “come of age,” being used to constrain design loadings for a major engineering application in New Zealand. This milestone has been accompanied by key studies of FGFs and probabilistic seismic hazard assessment (PSHA) in North America. On 11 September we held a half day workshop involving participants currently involved in research on FGFs and PSHA. The workshop came exactly three years after the last SCEC workshop on this topic, and provided an opportunity for researchers to discuss the latest work, unresolved issues, and future directions. The following sections provide a summary of the workshop.

Conveners Mark Stirling and Mike Oskin opened the workshop with welcomes and introductory comments. The message conveyed was that there had been milestones achieved in the last two years with FGFs being used to set the design motions for a large dam site in New Zealand, and in informing hazard for the Diablo Canyon power plant. These two workstreams could be viewed as FGF-PSHA research “coming of age”, through making the transition from science to practise. The main topics discussed at the workshop were: FGF fragility; FGF populations; completion of a major 15 year-long regional study of FGF ages and fragility in southern California; regional studies in the Pacific Northwest, eastern USA; Trona Pinnacles case study; and methods for using FGFs in PSHA. Workshop highlights are described in the sections below.

Intellectual Merit Fragile geologic features (FGFs) provide the only means of testing and evaluating probabilistic seismic hazard analyses (PSHA) for return periods greater than those of historical records. As such they have relevance to many areas of SCEC research: earthquake rupture models, ground motion models, earthquake physics, and the quantification of epistemic uncertainty in PSHA. The workshop was convened to bring together researchers leading the latest work, and to celebrate the important milestone "real world" applications of FGFs at Clyde Dam and Diablo Canyon.
Broader Impacts Some of our respective graduate students have been involved in aspects of FGF work, and have therefore enhanced their skillsets by addressing a multidisciplinary problem that combines earthquake geology, geomorphology, age dating techniques, engineering seismology, and PSHA. The transition of FGF studies from science to practise since our last workshop in 2019 represents a major milestone that will pave the way to greater confidence in setting design loadings for engineered structures.
Exemplary Figure Figure 1: The Clyde Dam site, where FGFs were used for the first time to set the design motions for a major engineered structure. The inset shows one of the schist FGFs focused on in the study. Images from Mark Stirling and Julian Thomson.