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The 2021 South Sandwich Island M_w 8.2 Earthquake: A Slow Event Sandwiched Between Regular Ruptures

Jia, Zhe and Zhan, Zhongwen and Kanamori, Hiroo (2022) The 2021 South Sandwich Island M_w 8.2 Earthquake: A Slow Event Sandwiched Between Regular Ruptures. Geophysical Research Letters, 49 (3). Art. No. e2021GL097104. ISSN 0094-8276. doi:10.1029/2021GL097104.

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We determined the rupture sequence of the 12 August 2021 M_w 8.2 South Sandwich Island earthquake which appears to be a complex sequence in both time and space. Notable tsunamis were recorded by tide gauges at global distances. Given the complexity of this event, we conducted a multiple subevent inversion on broadband seismograms, to resolve its complex variations of fault geometry, location, depth, and temporal characteristics. We found that the rupture initiated as a regular deep thrust earthquake; it then ruptured shallower and triggered a silent and dominantly slow subevent extending ∼200 km to the south, and ended with two other regular subevents. The total duration is ∼260 s, unusually long for an M_w 8.2 event. Our result is qualitatively consistent with other moment tensor solutions and the deviant m_B–M_w and M_S–M_w relations, and provides a more quantitative space-temporal pattern of this unusual sequence.

Item Type:Article
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URLURL TypeDescription Paper ItemIRIS ItemGeneric Mapping Tools ItemMATLAB ItemSeismic data ItemTide gauge data
Jia, Zhe0000-0003-0652-2646
Zhan, Zhongwen0000-0002-5586-2607
Kanamori, Hiroo0000-0001-8219-9428
Alternate Title:The 2021 South Sandwich Island Mw 8.2 earthquake: a slow event sandwiched between regular ruptures
Additional Information:© 2022. American Geophysical Union. Issue Online: 08 February 2022; Version of Record online: 08 February 2022; Manuscript accepted: 12 January 2022; Manuscript revised: 07 January 2022; Manuscript received: 22 November 2021. We thank the IRIS for providing public access ( to all the seismic data. We thank the IOC of UNESCO for providing public access ( to the tide gauge data. We thank Luis Rivera and Gregory Beroza for constructive discussions, and thank two anonymous reviewers for their comments. This work is supported by USGS grant G19AP00030. Data Availability Statement: All figures are plotted using GMT ( and MATLAB ( software. Seismic data are available on the IRIS Wilber 3 page ( Tide gauge data are available on the IOC sea level page (
Group:Seismological Laboratory
Funding AgencyGrant Number
Issue or Number:3
Record Number:CaltechAUTHORS:20211207-5685000
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Official Citation:Jia, Z., Zhan, Z., & Kanamori, H. (2022). The 2021 South Sandwich Island Mw 8.2 earthquake: A slow event sandwiched between regular ruptures. Geophysical Research Letters, 49, e2021GL097104.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112266
Deposited By: George Porter
Deposited On:08 Dec 2021 17:41
Last Modified:10 Feb 2022 17:22

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