Recent Trends in Seismicity Catalogs for the USGS National Seismic Hazard Model

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Seismicity catalogs and seismicity-based earthquake rate models for the conterminous United States were updated for the 2018 USGS National Seismic Hazard Model (NSHM). Since the previous NSHM update in 2014, new earthquakes in 2013–2017 were added, and parameters for some pre-2013 earthquakes were revised. Although the basic procedures for catalog construction and gridded-seismicity hazard modeling were unchanged, some details of the methodology such as regional moment magnitude estimation and catalog-completeness modeling were updated for 2018. There were significant rate changes where new earthquakes occurred in previously quiescent areas (for example, local increases in Delaware and southern Ohio) or where magnitudes were revised for some older earthquakes (local increases or decreases throughout the U.S.). Regional decreases in the intermountain west are attributed to a revised procedure for estimating moment magnitudes there. Induced earthquakes were included in special hazard studies in 2016, 2017, and 2018. Changes occurred in the Oklahoma–Kansas induced-seismicity belt, where an increase in activity in 2013–2014 was followed by a decrease in 2015–2017 (presumably reflecting efforts to mitigate earthquakes and trends in hydrocarbon production), and new earthquakes occurred westward of the established active zones. Interestingly, the recent overall decrease was not apparent in the declustered catalog; this paradoxical behavior in 2016 and 2017 may be related to the strong, but only short-term, declustering that followed three magnitude 5+ earthquakes in Oklahoma in 2016, and to limitations in our standard declustering methodology as applied to the Oklahoma-Kansas catalog. Changes will be illustrated with maps comparing results from the 2018 and 2014 NSHM.

Presenting Author: Charles S. Mueller

Authors