1707 Hōei earthquake

The southern coast of Honshu runs parallel to the Nankai Trough, which marks the subduction of the Philippine Sea plate beneath the Eurasian plate. Movement on this convergent plate boundary leads to many earthquakes, some of them of megathrust type. The Nankai megathrust has five distinct segments (A-E) that can rupture independently.{{cite journal|last=Ando|first=M.|year=1975|title=Source mechanisms and tectonic significance of historical earthquakes along the nankai trough, Japan|journal=Tectonophysics|volume=27|issue=2|pages=119–140|doi=10.1016/0040-1951(75)90102-X|bibcode=1975Tectp..27..119A}}{{cite journal|last=Ishibashi|first=K.|year=2004|title=Status of historical seismology in Japan|journal=Annals of Geophysics|volume=47|issue=2/3|pages=339–368|url=http://www.earth-prints.org/bitstream/2122/763/1/02Ishibashi.pdf|access-date=22 November 2009}} The segments have ruptured either singly or together repeatedly over the last 1,300 years.{{cite book|last=Sieh|first=K.E.|title=A Review of Geological Evidence for Recurrence Times of Large Earthquakes|year=1981|url=http://www.gps.caltech.edu/~sieh/pubs_docs/papers/P81b.pdf|access-date=13 November 2009|archive-date=4 June 2010|archive-url=https://web.archive.org/web/20100604120819/http://www.gps.caltech.edu/~sieh/pubs_docs/papers/P81b.pdf|url-status=dead}} Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them: In addition to two events in 1854, a similar pair occurred in 1944 and 1946. In both instances, the northeastern segment ruptured before the southwestern segment.{{cite book|last=Kaneda|first=Y.|author2=Kawaguchi, K.|author3=Araki, E.|author4=Matsumoto, H.|author5=Nakamura, T.|author6=Kamiya, S.|author7=Hori, T.|author8=Baba, T.|title=2007 Symposium on Underwater Technology and Workshop on Scientific Use of Submarine Cables and Related Technologies|chapter=Precise real-time observatory and simulating phenomena of earthquakes and tsunamis around the Nankai Trough – Towards the understanding of mega thrust earthquakes|year=2007|pages=299–300|doi=10.1109/UT.2007.370806|isbn=978-1-4244-1207-5|s2cid=45347574}} In the 1707 event, the earthquakes were either simultaneous, or close enough in time to not be distinguished by historical sources.

The earthquake caused 4,900–21,000 casualties, destroyed 29,000 houses, and triggered at least one major landslide, the Ohya slide in Shizuoka.{{cite journal|title=Large Sediment Movement Caused by the Catastrophic Ohya-Kuzure Landslide|last=Tsuchiya|first=S.|author2=Imaizumi F.|year=2010|journal=Journal of Disaster Research|volume=5|issue=3|pages=257–263|doi=10.20965/jdr.2010.p0257|doi-access=free}} One of Japan's three largest, it buried a 1.8 km² area under an estimated 120 million m³ of debris.{{cite web|url=http://www.nilim.go.jp/lab/bcg/siryou/tnn/tnn0277pdf/ks0277008.pdf|title=Case 2: Oya Hillside work|access-date=30 January 2010}} The Nara Basin shows evidence of event-induced liquefaction.{{cite journal|last=Nakanashi|first=I.|year=1999|title=Liquefaction Caused by the 1707 Hoei Earthquake as Observed in the Nara Basin, Central Japan|journal=Disaster Prevention Research Institute Annuals, Kyoto University|volume=42|issue=B1|pages=125–127|url=http://sciencelinks.jp/j-east/article/200005/000020000500A0102130.php|access-date=30 January 2010|url-status=dead|archive-url=https://web.archive.org/web/20120225235238/http://sciencelinks.jp/j-east/article/200005/000020000500A0102130.php|archive-date=25 February 2012}}

The magnitude of the 1707 event exceeded that of both the 1854 Tōkai and Nankai earthquakes, based on several observations. The uplift at Cape Muroto, Kōchi is estimated at {{cvt|2.3|m}} in 1707 compared to {{cvt|1.5|m}} in 1854, the presence of an area of seismic intensity of 6–7 on the JMA scale in Kawachi Plain, the degree of damage and inundations heights for the corresponding tsunami and records of tsunami at distant locations, such as Nagasaki and Jeju-do, Korea.{{cite web|url=http://www2.jpgu.org/meeting/2007/program/pdf/T235/T235-010_e.pdf|title=The 1707 Hoei Earthquake, as an Example of a combined Gigantic Tokai-Nankai Earthquake|last=Tsuji|first=Y.|author2=Namegaya Y.|year=2007|access-date=23 December 2009}}

The length of the rupture has been estimated from the modelling of the observed tsunami and the location of tsunami deposits. Initial estimates of 605 km, based on four segments rupturing failed to explain tsunami deposits discovered at the western end of the trough. Including an additional area at the southwestern end, part of the so-called Hyuga-nada segment, gave a better match, with a total rupture length in the range 675–700 km.{{Cite journal|last1=Kim|first1=S.|last2=Saito|first2=T.|last3=Fukuyama|first3=E.|last4=Kang|first4=T.-S.|date=2016|title=The Nankai Trough earthquake tsunamis in Korea: numerical studies of the 1707 Hoei earthquake and physics-based scenarios|url=https://core.ac.uk/download/pdf/208618327.pdf|journal=Earth, Planets and Space|volume=68|issue=1|page=64|doi=10.1186/s40623-016-0438-9|bibcode=2016EP&S...68...64K|doi-access=free}}{{Cite journal|last1=Furumura|first1=T.|last2=Imai|first2=K.|last3=Maeda|first3=T.|date=2011|title=A revised tsunami source model for the 1707 Hoei earthquake and simulation of tsunami inundation of Ryujin Lake, Kyushu, Japan|journal=Journal of Geophysical Research|volume=116|issue=B2|doi=10.1029/2010JB007918|bibcode=2011JGRB..116.2308F|doi-access=free}}

Approximately 16 hours after the mainshock, in the early morning of the following day at around 06:00 JST, a strong earthquake with a magnitude of 7.0 occurred with its epicenter near Fujinomiya. This earthquake was strongly felt in Edo (according to the "Diary of Archbishop Ryuko"), Toyama (as recorded in the "Yoshikawa Essays"), and Nagoya (as noted in the "Parrot Cage Records"). In the domain of the Murayama Sengen Shrine, all houses collapsed, and there were instances of temple and shrine buildings collapsing and fatalities in Fujinomiya and along the Tokaido route.{{Cite web|date=March 2011|title=2011年 東北地方太平洋沖地震 過去に起きた大きな地震の余震と誘発地震|url=http://outreach.eri.u-tokyo.ac.jp/eqvolc/201103_tohoku/inducedeq/|url-status=dead|archive-url=https://web.archive.org/web/20120328053737/http://outreach.eri.u-tokyo.ac.jp/eqvolc/201103_tohoku/inducedeq/|archive-date=28 March 2012|access-date=1 June 2024|website=outreach.eri.u-tokyo.ac}}

On 13 February 1708, at 10:00–12:00 JST, a major aftershock with its epicenter off the coast of the Kii Peninsula, occurred. This earthquake was strongly felt in Kyoto (according to the "Diary of Miscellaneous Affairs") and Nagoya (as noted in the "Parrot Cage Records"), and it generated a tsunami. In Kii, salt fields were flooded (according to the "History of Hainan Village"), and in Ise, it affected Yamada, Fukiage-cho, and Hitotsuboki, breaking the embankment of the Miyagawa River (as recorded in the "Jingu Bunko Manuscripts").

Along the southwestern coast of Kōchi, run-up heights averaged {{cvt|7.7|m}} with up to 10 m in places;{{cite journal|last=Hatori|first=T.|year=1981|title=Field investigations of the Nankaido Tsunamis in 1707 and 1854 along the South-west coast of Shikoku|journal=Bulletin Earthquake Research Institute|volume=56|pages=547–570|language=ja|url=http://repository.dl.itc.u-tokyo.ac.jp/dspace/bitstream/2261/12817/1/ji0563006.pdf|access-date=23 December 2009|archive-url=https://web.archive.org/web/20111006004423/http://repository.dl.itc.u-tokyo.ac.jp/dspace/bitstream/2261/12817/1/ji0563006.pdf|archive-date=6 October 2011|url-status=dead}} In Japanese. {{cvt|25.7|m}} high at Kure, Nakatosa, Kōchi, and {{cvt|23|m}} at Tanezaki.Akitsune Imamura. (1938). [https://www.jstage.jst.go.jp/article/zisin1929/10/9/10_9_394/_article/-char/ja/ 土佐に於ける宝永・安政両度津浪の高さ], 地震 第1輯, 10, 394–404. in Japanese.

{{Main|Hōei eruption}}

Evidence suggests that changes in stress caused by large earthquakes might be sufficient to trigger volcanic eruptions, assuming that the magma system involved is close to a critical state. The 1707 earthquake might have triggered a shift in static stress that led to pressure changes in the magma chamber beneath Mount Fuji. The volcano erupted on 16 December 1707, 49 days after the earthquake.

• {{Portal-inline|Japan}}
• List of earthquakes in Japan
• List of historical earthquakes
• List of megathrust earthquakes

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Category:1700s earthquakes

Hoei earthquake

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Category:Earthquakes of the Edo period

Category:18th-century disasters in Japan