Evaluation of seismic hazard models with fragile geologic features

Mark Stirling

In Preparation August 19, 2020, SCEC Contribution #10777

We provide an overview of a 2019 workshop on the use of fragile geologic features (FGFs) to evaluate seismic hazard models. FGFs have been scarcely utilized in the evaluation of seismic hazard models, despite nearly 30 years passing since the first recognition of their potential value. Several studies have recently begun to focus on implementation of FGFs in seismic hazard modelling. The workshop was held in order to capture a “snapshot” of the state of the art in FGF work, and to define key research areas that would increase confidence in FGF-based evaluation of seismic hazard models. It was held at the annual meeting of the Southern California Earthquake Center (SCEC) on 8 September 2019, and the conveners were Mark Stirling (University of Otago, New Zealand) and Michael Oskin (University of California, Davis). The workshop attracted 44 participants from a wide range of disciplines. The main topics of discussion were: FGF fragility age estimation (age at which a FGF achieved its current fragile geometry); fragility estimation; FGF-based evaluation of seismic hazard models; and ethical considerations relating to documentation and preservation of FGFs. There are now many scientists working on, or motivated to work on, FGFs, and more types of FGFs being worked on than just the precariously-balanced rock (PBR) variety. One of the ideas presented at the workshop is that fragility ages for FGFs should be treated stochastically rather than assuming all share a common age. In a similar vein, new studies propose more comprehensive methods of fragility assessment beyond peak ground acceleration and peak ground velocity-based approaches. Two recent studies that apply PBRs to evaluate probabilistic seismic hazard models use significantly different methods of evaluation. Key research needs identified from the workshop will guide future, focused efforts that will ultimately facilitate the uptake of FGFs in seismic hazard analysis.

Key Words
seismic hazard, PSHA, Fragile geologic feature, precariously-balanced rock, FGF, PBR, ground motion

Stirling, M. (2020). Evaluation of seismic hazard models with fragile geologic features. TBD, (in preparation).

Related Projects & Working Groups
Ground motions, Earthquake geology