A Caltech Library Service

Rupture Model for the 29 July 2021 M_W 8.2 Chignik, Alaska Earthquake Constrained by Seismic, Geodetic, and Tsunami Observations

Ye, Lingling and Bai, Yefei and Si, Daojun and Lay, Thorne and Cheung, Kwok Fai and Kanamori, Hiroo (2022) Rupture Model for the 29 July 2021 M_W 8.2 Chignik, Alaska Earthquake Constrained by Seismic, Geodetic, and Tsunami Observations. Journal of Geophysical Research. Solid Earth, 127 (7). Art. No. e2021JB023676. ISSN 2169-9313. doi:10.1029/2021jb023676.

[img] PDF - Accepted Version
See Usage Policy.

[img] PDF - Supplemental Material
See Usage Policy.

[img] Video (MPEG) (Movie S1) - Supplemental Material
See Usage Policy.

[img] Video (MPEG) (Movie S2) - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


A great earthquake struck the Semidi segment of the plate boundary along the Alaska Peninsula on 29 July 2021, re-rupturing part of the 1938 rupture zone. The 2021 M_W 8.2 Chignik earthquake occurred just northeast of the 22 July 2020 M_W 7.8 Simeonof earthquake, with little slip overlap. Analysis of teleseismic P and SH waves, regional Global Navigation Satellite System (GNSS) displacements, and near-field and far-field tsunami observations provides a good resolution of the 2021 rupture process. During ∼60-s long faulting, the slip was nonuniformly distributed along the megathrust over depths from 32 to 40 km, with up to ∼12.9-m slip in an ∼170-km-long patch. The 40–45 km down-dip limit of slip is well constrained by GNSS observations along the Alaska Peninsula. Tsunami observations preclude significant slip from extending to depths <25 km, confining all coseismic slip to beneath the shallow continental shelf. Most aftershocks locate seaward of the large-slip zones, with a concentration of activity up-dip of the deeper southwestern slip zone. Some localized aftershock patches locate beneath the continental slope. The surface-wave magnitude MS of 8.1 for the 2021 earthquake is smaller than Mₛ = 8.3–8.4 for the 1938 event. Seismic and tsunami data indicate that slip in 1938 was concentrated in the eastern region of its aftershock zone, extending beyond the Semidi Islands, where the 2021 event did not rupture.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemUSGS National Earthquake Information Center ItemIRIS Wilber 3 National Seismograph Network Data Collection Network Seismic Network ItemUNAVCO Bulletin Board
Ye, Lingling0000-0001-9689-4149
Bai, Yefei0000-0003-3323-3348
Lay, Thorne0000-0003-2360-4213
Cheung, Kwok Fai0000-0002-7435-0500
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 2022. American Geophysical Union. Issue Online: 10 July 2022. Version of Record online: 10 July 2022. Accepted manuscript online: 03 July 2022. Manuscript accepted: 25 June 2022. Manuscript revised: 20 June 2022. Manuscript received: 20 November 2021. We thank editor Rachel Abercrombie, associate editor Alice-Agnes Gabriel, reviewer Ronni Grapenthin, and an anonymous reviewer for helpful comments on the manuscript. The GNSS data are based on the services provided by the GAGE Facility, operated by UNAVCO, Inc., with support from the National Science Foundation and the National Aeronautics and Space Administration under NSF Cooperative Agreement EAR-1724794. The high-resolution digital elevation model, Sand Point V2, at the Shumagin Islands was downloaded from the Nation Centers for Environmental Information ( Lingling Ye's earthquake study was supported by the National Natural Science Foundation of China (No. 41874056). Yefei Bai's tsunami research was supported by the Finance Science and Technology Project of Hainan Province (No. ZDKJ202019). Thorne Lay's earthquake research was supported by the National Science Foundation (Grant EAR1802364). Data Availability Statement Earthquake information are based on the catalogs from the US Geological Survey National Earthquake Information Center (USGS-NEIC) ( All seismic data were downloaded through the IRIS Wilber 3 system ( with stations from Global Seismographic Network (II:, IU:, and International Federation of Digital Seismic Networks (FDSN; AU:, AZ:, C1:, CI:, CM:, CN:, CU:, DK, G:, GE:, IC:, and JP). We thank the facilities of IRIS Data Services, and specifically the IRIS Data Management Center, which were used for access to waveforms, related metadata, and/or derived products used in this study. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience (SAGE) Award of the National Science Foundation under Cooperative Support Agreement EAR-1851048. Coseismic static GNSS displacements were obtained from the UNAVCO Bulletin Board (
Group:Seismological Laboratory
Funding AgencyGrant Number
National Natural Science Foundation of China41874056
Finance Science and Technology Project of Hainan ProvinceZDKJ202019
Subject Keywords:Alaska-Aleutian trench; subduction zone earthquake; finite-fault inversion; tsunami modeling
Issue or Number:7
Record Number:CaltechAUTHORS:20220715-744516000
Persistent URL:
Official Citation:Ye, L., Bai, Y., Si, D., Lay, T., Cheung, K. F., & Kanamori, H. (2022). Rupture model for the 29 July 2021 MW 8.2 Chignik, Alaska earthquake constrained by seismic, geodetic, and tsunami observations. Journal of Geophysical Research: Solid Earth, 127, e2021JB023676.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115660
Deposited By: George Porter
Deposited On:18 Jul 2022 17:30
Last Modified:18 Jul 2022 17:30

Repository Staff Only: item control page