1707 Hōei earthquake

1707 Hōei earthquake
As6022014 · CC BY-SA 3.0 · source
Name	1707 Hōei earthquake
Native name	宝永地震
Date	1707-10-28 (Gregorian)
Magnitude	~8.6–8.7 Mw
Depth	shallow
Affected	Japan, Edo, Osaka, Kyoto, Tosa Province, Iyo Province, Awa Province, Tōtōmi Province
Casualties	estimates vary (tens of thousands)

1707 Hōei earthquake The 1707 Hōei earthquake struck southwestern Japan on 28 October 1707 (Gregorian), producing a major seismic rupture and a devastating tsunami that affected large parts of Honshū and Shikoku and is widely regarded as one of the largest historical events in Japanese seismic history. This event occurred during the Edo period under the rule of the Tokugawa shogunate and had profound effects on urban centers such as Edo, Osaka, and Kyoto, as well as on regional domains including Satsuma Domain and Tosa Domain.

Background and tectonic setting

The earthquake occurred in a complex plate boundary region where the Philippine Sea Plate interacts with the Eurasian Plate and the North American Plate near the Nankai Trough and the Suruga Trough. The event is associated with the segmented rupture behavior historically attributed to the Nankai megathrust and the adjacent Tōkai earthquake and Tōnankai earthquake segments. Historical precedents include the 1703 Genroku earthquake and earlier documented megathrust events recorded in Japanese chronicles and domainal records from the Muromachi period and the Sengoku period. Seismic coupling along the interface beneath Shikoku, Kii Peninsula, and the Izu Peninsula was a key factor in the accumulation of elastic strain leading to failure.

Earthquake characteristics and rupture

Contemporary analyses estimate the event magnitude at approximately 8.6–8.7 Mw based on tsunami heights, coastal subsidence, and paleoseismological data from the Kaya archaeological site and coastal marsh sequences near Ostracon Bay (local names in sources). The rupture likely involved simultaneous failure of multiple megathrust segments including portions attributed to the Nankai Trough, Tōnankai and Tōkai zones, producing long rupture lengths exceeding several hundred kilometers. Geological evidence for coseismic displacement includes raised marine terraces studied at Aoshima and subsidence documented in coastal plains such as the Nara Basin. Indicators of strong shaking are preserved in structural collapses recorded in castle inventories of Himeji Castle, Nagoya Castle, and Sunpu Castle.

Tsunami and coastal impacts

The earthquake generated a transoceanic tsunami that inundated coastlines across Shikoku, Awaji Island, the Kii Peninsula, and parts of Kyūshū, with reported run-up heights varying by location. Tsunami effects were recorded in contemporary domainal reports from Satsuma Domain, Tosa Domain, Iyo Province, and Awa Province, and mentioned in correspondence kept in the archives of the Tokugawa shogunate at Edo Castle. Maritime losses affected shipping routes connected to ports such as Osaka Bay, Yamada Bay, and Hakata Bay. Coastal geomorphology studies at Cape Muroto and sedimentary sequences in lagoonal basins provide stratigraphic confirmation of the 1707 tsunami deposits, corroborated by radiocarbon dating of mollusk shells and buried peat sequences.

Damage, casualties, and social consequences

Damage estimates derived from domainal censuses and temple registries indicate widespread destruction of residences, agricultural fields, and infrastructure across Honshū and Shikoku. Major urban centers like Edo and Osaka reported collapsed dwellings, fires, and disruptions to granary supplies managed by daimyo administrations including Kaga Domain and Mito Domain. Casualty tallies are uncertain but contemporaneous reports and later compilations by bakufu officials suggest deaths in the tens of thousands, with many more displaced. The disaster exacerbated famines in affected regions by destroying irrigation works and rice paddies maintained under systems documented in land survey records and domainal tax registers. Social consequences included migrations recorded in village ledgers, strain on relief distributed by prominent figures such as Asano Naganori (family records) and responses by magistrates in Edo Castle.

Response, recovery, and reconstruction

The Tokugawa shogunate coordinated relief through daimyō requisitions, rice transfers, and rebuilding directives issued from Edo Castle and administered via regional magistrates in Osaka and provincial headquarters. Reconstruction efforts involved repair of seawalls, rebuilding of shrines and temples such as Kōyasan and local Shinto structures, and reestablishment of transportation corridors like the Tōkaidō road. Domainal records from Kii Province and Tosa Domain document mobilization of labor for flood control projects and reorganization of rice storage under magistrates modeled after practices in Hiroshima Domain and Satsuma Domain. Long-term demographic shifts are visible in parish registries and cadastral surveys used for later cadastral reforms.

Scientific research and significance

Modern seismology, paleoseismology, and tsunami modeling have used the 1707 event as a benchmark for understanding megathrust behavior in the Nankai Trough region, informing seismic hazard assessments for Tokyo, Nagoya, and Kobe. Research groups from institutions such as University of Tokyo, Tohoku University, and the National Research Institute for Earth Science and Disaster Resilience have integrated historical documents from domainal archives, dendrochronology, and radiocarbon constraints to reconstruct rupture scenarios and recurrence intervals for the Nankai megathrust. The event has also influenced modern disaster planning by agencies like the Japan Meteorological Agency and municipal authorities in Shizuoka Prefecture and Wakayama Prefecture, shaping tsunami inundation maps, early warning protocols, and coastal zoning regulations. Ongoing interdisciplinary studies continue to refine estimates of slip distribution and cascade rupture potential between adjacent megathrust segments, with implications for seismic risk reduction across Japan.

Category:Earthquakes in Japan Category:1707 in Japan Category:Megathrust earthquakes