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Intraplate Omori Decay Parameters and Spatiotemporal Distribution 145 Recent Central and Eastern North American Sequences

Description: 

Aftershock clusters are transient so must be identified and culled—“declustered”—from earthquake catalogs to calculate the long-term earthquake rates that are used to map seismic hazard in intraplate areas such as central and eastern North America (CENA). Despite this importance and the known differences between aftershock behavior in low strain-rate settings like CENA and tectonically active regions, estimates of aftershock sequence duration and the epicentral radius affected are based on California-type plate-boundary sequences. Here, Omori parameters for 145 intraplate CENA earthquake sequences (1974–2021, mainshocks M_w3.65–5.84) demonstrate significantly slower aftershock rate-decay than existing plate-boundary models, with major regional variations. The slope of log-rate vs time—Omori’s parameter p—averages 0.86±0.03 in the central/eastern U.S. sequences and 0.87±0.02 in the Charlevoix Seismic Zone, yet the rest of southeastern Canada averages p=1.02±0.05 similar to generic California behavior (p=1.07±0.03). Post-mainshock earthquake rates are only significantly elevated within ~15 km of the CENA mainshocks (up to 25 km for M5+ mainshocks) and remain so for 10^3±1 days—months to a decade or two. While California declustering models may clip events within 0.15 years and 30 km of a M4 mainshock (0.3 years, 40 km for M5), windows of 4 year and 15 km (8 years, 20 km for M5) appear more appropriate for CENA. Using these longer-duration yet smaller aftershock windows would reduce hazard bulls-eyes adjacent to historical earthquakes.

Session: Deciphering Earthquake Clustering for the Better Understanding of Crustal Deformation Mechanisms [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Will Levandowski

Student Presenter: No

Invited Presentation: 

Authors