2021 Chapter Meetings

Assessing the Influence of Epistemic Uncertainties on Earthquake Loss Estimates for California

Edward (Ned) H. Field, Research Geophysicist, USGS

EERI, New England Chapter, Lecture Series

Tuesday April 27, 2021, 12:00 – 1:00 PM (Eastern Time)

The Zoom Seminar is FREE!

For registration, please visit: HERE

Abstract: To aid in setting scientific research priorities, we assess the potential value of removing each of the epistemic uncertainties currently represented in the US Geological Survey California seismic-hazard model, using average annual loss (AAL) as the risk metric of interest. Given all the uncertainties, represented with logic-tree branches, we find a mean AAL of $3.94 billion. The modal value is 17.5% lower than the mean, and there is a 78% chance that the true AAL value is more than 10% away from the mean, and a 5% chance that it is a factor 2.1 greater or lower than the mean. We quantify the extent to which resolving each uncertainty improves the AAL estimate. The most influential branch is one that adds additional epistemic uncertainty to ground motion models, but others are found to be influential as well, such as the rate of M ≥ 5 events throughout the region. We discuss the broader implications of our findings, and note that the time dependence caused by spatiotemporal clustering can be much more influential on AAL than the epistemic uncertainties explored here.

Biography: Edward (Ned) Field has been a research geophysicist with USGS since 2000. He specializes in the development of earthquake-forecast models, which are one of the two main modeling components used in modern seismic-hazard analysis (the other being ground-motion models). His focus area has mainly been California, which due to an abundance of scientific talent and data constraints, has enabled the forging of state-or-the-art methodologies. Ned has led the development of the Third Uniform California Earthquake Rupture Forecast (UCERF3), representing both multi-fault ruptures and spatiotemporal clustering (e.g., aftershocks); the relevance of both these effects was dramatically exemplified in a recent sequence of damaging earthquakes in New Zealand. These forecast models influence a variety of risk mitigation activities, including building codes and catastrophe models used by insurance industry. Important themes he is focused on nowadays include: a better quantification of uncertainties; the use of more physics-based approaches; and the need to add “valuation” to verification and validation protocols. Ned has also led the development of OpenSHA, which is an open-source, and platform-independent computational framework for conducting seismic hazard analysis, which supports loss modeling as well. He is also an active member of the planning committee of the Southern California Earthquake Center.

Lecture Flyer (PDF)

Are Small Earthquakes a Big Deal?

Julian J Bommer, Senior Research Investigator, Faculty of Engineering, Dept. of Civil and Environmental Engineering, Imperial College, London

Friday February 5, 2021, 12:00 PM Eastern Time (US & Canada), Virtual Event

Tufts CEE Seminar Series and Joyner Lecture at The New England Chapter of EERI Present

Abstract: Earthquake engineering has traditionally focused on protecting society against the effects of large magnitude earthquakes but in recent years there has been increasing interest regarding the impact of smaller earthquakes. This has been driven partly by the occurrence of some low-magnitude earthquakes that have been cause unexpected levels of damage and particularly by the heightened concern regarding earthquakes of anthropogenic origin. The lecture begins by re-visiting the often-misunderstood rationale behind the exclusion of smaller magnitude earthquakes from probabilistic seismic hazard analysis as being related to the risk posed by such events. A number of case histories of small magnitude events reported to have caused damage are then reviewed, highlighting in each case the specific factors contributing to the impact and in some cases arguing that the impact may have been exaggerated. This is followed by a global analysis of small-to-moderate magnitude earthquakes to ascertain the likelihood of these resulting in damage and/or injury. As well as looking at the smallest magnitude earthquakes that have caused structural damage, the question of the smallest magnitudes required to trigger liquefaction is also addressed. The lecture concludes with some insights regarding if and when smaller earthquakes should be a concern as well as discussing the challenges associated with modelling the resulting hazard and risk that such events can pose.

Please Register for Seminar: HERE

Lecture Flyer (PDF)