Coseismic coastal subsidence associated with unusually wide rupture of prehistoric earthquakes on the Kamchatka subduction zone: A record in buried erosional scarps and tsunami deposits.

Pinegina, T. K., Bourgeois, J., Bazanova, L. I., Zelenin, E. A., Krasheninnikov, S. P. and Portnyagin, Maxim V. (2020) Coseismic coastal subsidence associated with unusually wide rupture of prehistoric earthquakes on the Kamchatka subduction zone: A record in buried erosional scarps and tsunami deposits. Quaternary Science Reviews, 233 (Article number 106171). DOI 10.1016/j.quascirev.2020.106171.

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Supplementary data:

Abstract

Highlights

• Unprecedented record of 3 unusually wide earthquakes (of >30) in last 4000 years.
• Of 5 historical earthquakes on this subduction-zone segment, none is comparable.
• Tephra correlation of coseismic subsidence, tsunamis and buried beach scarps.
• New methods quantify subsidence, tsunami size, erosional retreat for each event.
• New insights into millennial-scale variability of subduction-zone behavior.

Abstract

The prograding strand plain of Avachinsky Bay, Kamchatka, Russia, along the highly active Kamchatka subduction zone, exhibits geological evidence--buried erosional scarps--for coseismic subsidence only three times in the last four millennia, the last event about 1200 years ago. This same coast has a historical record (since A.D. 1737) of five subduction-zone earthquakes with large tsunami runup (>5 m), the last of which was the 1952 Mw 9 Kamchatka earthquake, and a geological record of more than 30 large tsunamis in the last 4000 years. This rarity of buried scarps relative to large earthquakes contrasts with the Cascadia strand plain in SW Washington State, where most or all large events are represented by buried scarps. A strong factor in the amplitude and sign of coseismic deformation is distance from the seaward edge of a subduction zone (the trench); the Avachinsky Bay coastline is 180–200 km from the trench, with ∼25° slab dip, requiring unusually wide ruptures to generate significant coseismic subsidence. This coastal zone is undergoing net subsidence approximately equivalent to the total of the three coseismic subsidence events, generating a sequence of beach ridges that increase in elevation seaward.

Each of the three unusual (coseismic subsidence) events comprises a) an earthquake whose deformation field caused b) onshore coseismic subsidence, thus local sea-level rise and c) sufficient deformation offshore to produce a large tsunami; a,b,c followed by d) a period of coastal erosion and shoreline retreat, leaving e) an erosional beach scarp that was f) subsequently buried once progradation resumed. We identified, dated and correlated the scarps and tsunami deposits from these events with several field methods, including trenching, tephrostratigraphy and ground penetrating radar. The scarps were correlated over an alongshore distance of 50–70 km. The most recent event (event 1) occurred ∼800 cal AD (1100–1250 14С years BP), event 2–600 cal BC (2400–2450 14С years BP), and event 3–1700 cal BC (3300–3500 14С years BP). We developed methods for quantifying subsidence, coastal erosion and tsunami size for each of these events. All three retain evidence of ∼0.4–1.2 m of coseismic subsidence; coastal erosion in the case of event 1 averaged more than 100 m; all three “event” tsunamis were amongst the largest in the last 4000 years.

Document Type: Article
Keywords: Holocene, Paleoseismology, Kamchatka subduction zone, Geomorphology, Coastal, Ground penetrating radar, Tephrochronology, Coseismic coastal subsidence, Buried erosional scarps, Tsunami deposits, Beach ridges
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Refereed: Yes
Open Access Journal?: No
Publisher: Elsevier
Date Deposited: 02 Mar 2020 08:01
Last Modified: 08 Feb 2023 09:39
URI: https://oceanrep.geomar.de/id/eprint/49085

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