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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/nhess-2017-172
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
20 Jun 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Natural Hazards and Earth System Sciences (NHESS).
1997 Kronotsky earthquake and tsunami and their predecessors, Kamchatka, Russia
Joanne Bourgeois1 and Tatiana K. Pinegina2 1Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195-1310, USA
2Institute of Volcanology and Seismology, FEB RAS, 9 Piip Boulevard, Petropavlovsk-Kamchatsky, 683006, Russia
Abstract. The northern segment of the Kamchatka subduction zone (KSZ) experienced three tsunamigenic earthquakes in the 20th century (Feb 1923, April 1923, Dec 1997), events that help us better understand the behavior of this segment. Characterizing these historical earthquakes and tsunamis in turn contributes to interpreting the prehistoric record, which is necessary to evaluate recurrence intervals for such events. A particular focus of this study is the nature and location of the 5 December 1997 Kronotsky rupture as elucidated by tsunami runup in southern Kamchatsky Bay. Some studies have characterized the subduction zone off Kronotsky Peninsula as less seismogenic, as indicated by gravity-anomaly analyses, and have placed the 1997 rupture south of the promontory. However, tsunami runup north of the peninsula, as evidenced by our mapping of tsunami deposits, requires the rupture to extend farther north. Previously reported runup (1997 tsunami) on Kronotsky Peninsula was no more than 2–3 m, but our studies indicate tsunami heights for at least 50 km north of the peninsula, ranging from 3.4 to 9.5 m (average 6.1 m), exceeding beach ridge heights of 5.3 to 8.3 m (average 7.1 m). For the two 1923 tsunamis, we cannot distinguish their deposits in southern Kamchatsky Bay, but they are in sum more extensive than the 1997 deposit. A reevaluation of the April 1923 earthquake (and its tsunami) suggests that its moment magnitude should be revised upward to Mw ~8. This revision makes the two 1923 events more like a pair, with the 1997 earthquake filling a gap between them. Deeper in time, the 1700-year prehistoric record of tsunamis in southern Kamchatsky Bay indicates that during this interval, there were no local events significantly larger than the 20th century earthquakes. Together, the historic and prehistoric record suggests a more northerly location of the 1997 rupture, a revision of the size of the April 1923 earthquake, and agreement with previous work suggesting the northern KSZ ruptures in smaller sections than the southern KSZ. The latter conclusion requires caution, however, as we continue to learn that our historic and even pre-historic records of earthquakes and tsunamis is limited, in particular as applied to hazard analysis. This study is a contribution to our continued efforts to understand tectonic behavior around the northern Pacific and in subduction zones, in general.

Citation: Bourgeois, J. and Pinegina, T. K.: 1997 Kronotsky earthquake and tsunami and their predecessors, Kamchatka, Russia, Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2017-172, in review, 2017.
Joanne Bourgeois and Tatiana K. Pinegina
Joanne Bourgeois and Tatiana K. Pinegina
Joanne Bourgeois and Tatiana K. Pinegina

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Short summary
The 5 Dec 1997 magnitude 7.8 Kronotsky earthquake and tsunami occurred on a dark night in an unpopulated area. A limited (Dec 97) post-tsunami survey found relatively small runup, which influenced some earthquake analyses. Years later, to our surprise, we discovered an extensive tsunami deposit up to 9 m above sea level on an unexplored coastal sector. Our tsunami runup data require reevaluation of earthquake rupture location and characteristics, and of the northern Kamchatka subduction zone.
The 5 Dec 1997 magnitude 7.8 Kronotsky earthquake and tsunami occurred on a dark night in an...
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