The 1944 Tōnankai earthquake occurred at 13:35 local time (04:35 UTC) on 7 December. It had an estimated magnitude of 8.1 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...

(making it the strongest known earthquake of 1944) and a maximum felt intensity of greater than 5 Shindo (about VIII (''Severe'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...

). It triggered a large tsunami that caused serious damage along the coast of

Wakayama Prefecture is a prefecture of Japan located in the Kansai region of Honshu. Wakayama Prefecture has a population of 876,030 () and a geographic area of . Wakayama Prefecture borders Osaka Prefecture to the north, and Mie Prefecture and Nara Prefecture to ...

and the

Tōkai region The is a subregion of the Chūbu region and Kansai region in Japan that runs along the Pacific Ocean. The name comes from the Tōkaidō, one of the Edo Five Routes. Because Tōkai is a sub-region and is not officially classified, there is ...

. Together, the earthquake and tsunami caused 3,358 casualties.

Tectonic setting

The southern coast of Honshū runs parallel to the

Nankai Trough The is a submarine trough located south of the Nankaidō region of Japan's island of Honshu, extending approximately offshore. The underlying fault, the ''Nankai megathrust,'' is the source of the devastating Nankai megathrust earthquakes, ...

, which marks the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the

Philippine Sea plate The Philippine Sea plate or the Philippine plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

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, the segments have ruptured either singly or together repeatedly over the last 1300 years. Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them. The 1944 event, which ruptured the C & D segments was followed two years later by the 1946 Nankaidō earthquake, rupturing segments A & B. In addition to these two events, there were two similar earthquakes in 1854. In each case the northeastern segment ruptured before the southwestern segment.

Damage

There was severe damage from the earthquake on the eastern side of the Kii Peninsula particularly in the cities of Shingū and Tsu. A total of 26,146 houses were destroyed by the shaking, including 11 that burned down and a further 3,059 houses were destroyed by the tsunami. Nearly 47,000 houses were seriously damaged by the combined effects of the earthquake and tsunami. A total of 1,223 people were killed and a further 2,135 were seriously injured.

Characteristics

Earthquake

Felt intensities of greater than Shindo 5 were recorded along the southern coast of Honshū, with Shindo 3–4 in Tokyo. The observed teleseismic response and tsunami records have been matched using a rupture area of 220 x 140 km and a maximum displacement of 2.3 m. It has been suggested that splay faults, linking back into the plate interface, had an important role in generating large tsunamigenic earthquakes along the Nankai trough. The 1944 event could have occurred on such a splay fault.

Tsunami

The maximum recorded wave height was 10 meters on the Kumano coast. Run-ups in excess of 5 meters were also recorded at several locations along the coasts of Mie and

s. The tsunami was observed along the Pacific coast of Japan from

Izu Peninsula The is a mountainous peninsula with a deeply indented coastline to the west of Tokyo on the Pacific Ocean, Pacific coast of the island of Honshu, Japan, the largest of the four main islands of Japan. Formerly known as Izu Province, Izu peninsu ...

Kyushu is the third-largest island of Japan's Japanese archipelago, four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa Island, Okinawa and the other Ryukyu Islands, Ryukyu (''Nansei'') Ryukyu Islands, Islands ...

, and recorded by tide gauges from Alaska to Hawaii.

Future seismic hazard

The segment of the megathrust to the east of the rupture area for the 1944 earthquake has not ruptured since 1854 and the likelihood of a ' Tōkai earthquake' to the east of this earthquake is considered to be high. There is no evidence that this segment has ruptured on its own in the past, although this cannot be ruled out. Any rupture of segment E may also include segments C & D, possibly causing a repeat of the damaging 1854 Tōkai earthquake.

References

External links

* {{DEFAULTSORT:Tonankai earthquake, 1944 1944 Tonankai 1944 earthquakes 1944 in Japan

1944 Events Below, the events of World War II have the "WWII" prefix. January * January 2 – WWII: ** Free France, Free French General Jean de Lattre de Tassigny is appointed to command First Army (France), French Army B, part of the Sixt ...

History of Mie Prefecture History of Wakayama Prefecture 1944 Tonankai 1940s tsunamis December 1944 in Asia Earthquakes of the Showa era