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Rapid shallow megathrust afterslip from the 2021 M8.2 Chignik, Alaska earthquake revealed by seafloor geodesy

April 26, 2023

The shallower portions of subduction zone megathrust faults host Earth’s most hazardous tsunamigenic earthquakes, yet understanding how and when they slip remains elusive because of challenges making seafloor observations. We performed Global Navigation Satellite System Acoustic seafloor geodetic surveys before and ~2.5 months after the 29 July 2021 Mw (moment magnitude) 8.2 Chignik, Alaska, earthquake and determine ~1.4 meters cumulative co- and post-seismic horizontal displacement ~60 kilometers from the megathrust front. Only for the 2011 Mw 9 Tohoku event have closer subduction zone earthquake displacements been observed. We estimate ~2 to 3 meters of megathrust afterslip shallower than 20 kilometers, a portion of the megathrust on which both inter- and co-seismic slip likely had occurred previously. Our analysis demonstrates that by 2.5 months, shallower and deeper moment had effectively equilibrated on the megathrust, suggesting that its tsunamigenic potential remains no more elevated than before the earthquake.

Publication Year 2023
Title Rapid shallow megathrust afterslip from the 2021 M8.2 Chignik, Alaska earthquake revealed by seafloor geodesy
DOI 10.1126/sciadv.adf9299
Authors Benjamin A. Brooks, Dara Elyse Goldberg, John DeSanto, Todd Ericksen, Spahr Webb, Scott Nooner, C. David Chadwell, James H. Foster, Sarah E. Minson, Robert Witter, Peter J. Haeussler, Jeffery T. Freymueller, William D. Barnhart, Johanna Nevitt
Publication Type Article
Publication Subtype Journal Article
Series Title Science Advances
Index ID 70263675
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center
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