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Published April 2025 | Version Published
Journal Article Open

The 2021 Mw 8.1 Kermadec Earthquake Sequence: Great Earthquake Rupture Along the Mantle/Slab Contact

Creators

  • 1. ROR icon Southern University of Science and Technology
  • 2. ROR icon University of California, Santa Cruz
  • 3. ROR icon Institute of Geology and Geophysics
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon National Institute of Geophysics and Volcanology
  • 6. ROR icon Institute of Oceanology

Abstract

Most great earthquakes on subduction zone plate boundaries have large coseismic slip concentrated along the contact between the subducting slab and the upper plate crust. On 4 March 2021, a magnitude 7.4 foreshock struck 1 hr 47 min before a magnitude 8.1 earthquake along the northern Kermadec island arc. The mainshock is the largest well-documented underthrusting event along the ∼2,500-km long Tonga-Kermadec subduction zone. Using teleseismic, geodetic, and tsunami data, we find that all substantial coseismic slip in the mainshock is located along the mantle/slab interface at depths from 20 to 55 km, with the large foreshock nucleating near the down-dip edge. Smaller foreshocks and most aftershocks are located up-dip of the mainshock, where substantial prior moderate thrust earthquake activity had occurred. The upper plate crust is ∼17 km thick in northern Kermadec with only moderate-size events along the crust/slab interface. A 1976 sequence with MW values of 7.9, 7.8, 7.3, 7.0, and 7.0 that spanned the 2021 rupture zone also involved deep megathrust rupture along the mantle/slab contact, but distinct waveforms exclude repeating ruptures. Variable waveforms for eight deep M6.9+ thrusting earthquakes since 1990 suggest discrete slip patches distributed throughout the region. The ∼300-km long plate boundary in northern Kermadec is the only documented subduction zone region where the largest modeled interplate earthquakes have ruptured along the mantle/slab interface, suggesting that local frictional properties of the putatively hydrated mantle wedge may involve a dense distribution of Antigorite-rich patches with high slip rate velocity weakening behavior in this locale.

Copyright and License

© 2025. American Geophysical Union.

Acknowledgement

We thank Laura M. Wallace, Kelin Wang, Emily Brodsky, Heather Savage, Shiqing Xu, and Jeff Freymueller for helpful discussions, the editor Satoshi Ide, the associate editor, and anonymous reviewers for their thoughtful comments and suggestions which helped improve the manuscript.

Funding

The work was supported in part by National Key R&D Program of China 2023YFF0803200 (L. Y.), National Natural Science Foundation of China (42474077, 42494864, 42494860, and 42106074), and National Science Foundation Grant EAR1802364 (T. L.).

Data Availability

All body wave and surface wave recordings from global seismic stations that were used were downloaded from the Incorporated Research Institutions for Seismology (IRIS) data management center (IRIS, 2025). This included 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) as well as High Gain Long Period (HG) stations. 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. Earthquake source mechanisms from the Global Centroid Moment Tensor project (Ekström et al., 2012) were used in this paper. Earthquake information is based on the catalogs of the National Earthquake Information Center at the U.S. Geological Survey (USGS-NEIC, 2025) and International Seismological Center (ISC, 2025). Kristine Larson provided the RAUL 30-s GPS signals, processed by the Canadian Geodetic Survey of Natural Resources, Canada, Canadian Spatial Reference System Precise Point Positioning service (CSRS-PPP, 2025). Daily solutions for RAUL were obtained from the Nevada Geodetic Laboratory (NGL, 2025). Tide gauge sea level data are obtained from IOC UNESCO (2025); New Zealand DART data are from GNS Science (2020). This work made use of GMT (Wessel et al., 2019) and SAC (Goldstein et al., 2003).

Supplemental Material

Supporting Information S1 (PDF)

Files

JGR Solid Earth - 2025 - Ye - The 2021 MW 8 1 Kermadec Earthquake Sequence Great Earthquake Rupture Along the Mantle Slab.pdf

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Additional details

Related works

Is supplemented by
Supplemental Material: https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1029%2F2024JB030926&file=2024JB030926-sup-0001-Supporting+Information+SI-S01.pdf (URL)

Funding

Ministry of Science and Technology of the People's Republic of China
National Key R&D Program 2023YFF0803200
National Natural Science Foundation of China
42474077
National Natural Science Foundation of China
42494864
National Natural Science Foundation of China
42494860
National Natural Science Foundation of China
42106074
National Science Foundation
EAR-1802364

Dates

Accepted
2025-03-24
Available
2025-04-02
Version of record online
Available
2025-04-02
Issue online

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Caltech groups
Seismological Laboratory, Division of Geological and Planetary Sciences (GPS)
Publication Status
Published