Ultra-long period and small-amplitude tsunami generated following the July 2020 Alaska Mw7.8 tsunamigenic earthquake

Mohammad Heidarzadeh; Iyan E. Mulia

doi:10.1016/j.oceaneng.2021.109243

Ultra-long period and small-amplitude tsunami generated following the July 2020 Alaska M_w7.8 tsunamigenic earthquake

Mohammad Heidarzadeh, Iyan E. Mulia

Research output: Contribution to journal › Article › peer-review

12 Citations (SciVal)

Abstract

The July 2020 M_w7.8 Alaska tsunamigenic earthquake was a fresh call for potential large tsunamis associated with the Aleutian subduction zone. The second largest ever-recorded earthquake worldwide (M_w 9.2) occurred in this zone in 1964 indicating its massive earthquake and tsunami risk. Our analysis of the July 2020 tsunami revealed that it involves very long period waves (51–64 min) which is unusual for an M_w7.8 earthquake. The tsunami coastal amplitude was small (~0.5 m) which is much smaller than that usually expected from a tsunamigenic earthquake of this size. Here, through numerical simulations and spectral analyses, we explain the ultra-long period and small amplitude waves of the tsunami. Our analysis using an analytical equation showed that the ultra-long period of the tsunami (51–64 min) can be reproduced using the shallow water depth around the source region (100–200 m) and the length of the coseismic deformation area (~100 km). By comparing the coastal amplitude of this event with four other similar-size and similar-mechanism earthquakes (thrust M_w7.8), we attribute the relatively small coastal amplitude of this tsunami to the deep focal depth of the earthquake (28 km) and the extremely shallow water around the source region.

Original language	English
Article number	109243
Journal	Ocean Engineering
Volume	234
Early online date	6 Jun 2021
DOIs	https://doi.org/10.1016/j.oceaneng.2021.109243
Publication status	Published - 15 Aug 2021

Bibliographical note

Funding Information:
The tide gauge data used in this research are provided by the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (IOC) of the United Nations ( http://www.ioc-sealevelmonitoring.org/index.php ) and the United States National Oceanic and Atmospheric Administraion's Deep-ocean Assessment and Reporting of Tsunamis (DART) program ( https://nctr.pmel.noaa.gov/Dart/ ). We are sincerely grateful to an anonymous reviewer for the constrictive review comments. MH is funded by the Royal Society (the United Kingdom), grant number CHL\R1\180173 . A number of figures were drafted using the GMT software ( Wessel and Smith, 1998 ). The authors declare that they have no competing interests regarding the work presented in this paper. Authors are grateful to two anonymous reviewers for their constructive comments.

Funding Information:
The tide gauge data used in this research are provided by the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (IOC) of the United Nations (http://www.ioc-sealevelmonitoring.org/index.php) and the United States National Oceanic and Atmospheric Administraion's Deep-ocean Assessment and Reporting of Tsunamis (DART) program (https://nctr.pmel.noaa.gov/Dart/). We are sincerely grateful to an anonymous reviewer for the constrictive review comments. MH is funded by the Royal Society (the United Kingdom), grant number CHL\R1\180173. A number of figures were drafted using the GMT software (Wessel and Smith, 1998). The authors declare that they have no competing interests regarding the work presented in this paper. Authors are grateful to two anonymous reviewers for their constructive comments.

Publisher Copyright:
© 2021 The Authors

Keywords

Alaska
Aleutian subduction zone
Earthquake
Numerical simulations
Pacific ocean
Tsunami

ASJC Scopus subject areas

Environmental Engineering
Ocean Engineering

Access to Document

10.1016/j.oceaneng.2021.109243Licence: CC BY

Cite this

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title = "Ultra-long period and small-amplitude tsunami generated following the July 2020 Alaska Mw7.8 tsunamigenic earthquake",

abstract = "The July 2020 Mw7.8 Alaska tsunamigenic earthquake was a fresh call for potential large tsunamis associated with the Aleutian subduction zone. The second largest ever-recorded earthquake worldwide (Mw 9.2) occurred in this zone in 1964 indicating its massive earthquake and tsunami risk. Our analysis of the July 2020 tsunami revealed that it involves very long period waves (51–64 min) which is unusual for an Mw7.8 earthquake. The tsunami coastal amplitude was small (~0.5 m) which is much smaller than that usually expected from a tsunamigenic earthquake of this size. Here, through numerical simulations and spectral analyses, we explain the ultra-long period and small amplitude waves of the tsunami. Our analysis using an analytical equation showed that the ultra-long period of the tsunami (51–64 min) can be reproduced using the shallow water depth around the source region (100–200 m) and the length of the coseismic deformation area (~100 km). By comparing the coastal amplitude of this event with four other similar-size and similar-mechanism earthquakes (thrust Mw7.8), we attribute the relatively small coastal amplitude of this tsunami to the deep focal depth of the earthquake (28 km) and the extremely shallow water around the source region.",

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author = "Mohammad Heidarzadeh and Mulia, {Iyan E.}",

note = "Funding Information: The tide gauge data used in this research are provided by the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (IOC) of the United Nations ( http://www.ioc-sealevelmonitoring.org/index.php ) and the United States National Oceanic and Atmospheric Administraion's Deep-ocean Assessment and Reporting of Tsunamis (DART) program ( https://nctr.pmel.noaa.gov/Dart/ ). We are sincerely grateful to an anonymous reviewer for the constrictive review comments. MH is funded by the Royal Society (the United Kingdom), grant number CHL\R1\180173 . A number of figures were drafted using the GMT software ( Wessel and Smith, 1998 ). The authors declare that they have no competing interests regarding the work presented in this paper. Authors are grateful to two anonymous reviewers for their constructive comments. Funding Information: The tide gauge data used in this research are provided by the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (IOC) of the United Nations (http://www.ioc-sealevelmonitoring.org/index.php) and the United States National Oceanic and Atmospheric Administraion's Deep-ocean Assessment and Reporting of Tsunamis (DART) program (https://nctr.pmel.noaa.gov/Dart/). We are sincerely grateful to an anonymous reviewer for the constrictive review comments. MH is funded by the Royal Society (the United Kingdom), grant number CHL\R1\180173. A number of figures were drafted using the GMT software (Wessel and Smith, 1998). The authors declare that they have no competing interests regarding the work presented in this paper. Authors are grateful to two anonymous reviewers for their constructive comments. Publisher Copyright: {\textcopyright} 2021 The Authors",

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