The 1940 Shakotan earthquake occurred on August 2 at 00:08:22 JST with a moment magnitude () of 7.5 and maximum JMA seismic intensity of ''Shindo'' 4. The shock had an epicenter off the coast of

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

, Japan. Damage from the shock was comparatively light, but the accomanying tsunami was destructive. The tsunami caused 10 deaths and 24 injuries on Hokkaido, and destroyed homes and boats across the Sea of Japan. The highest tsunami waves () were recorded at the coast of Russia while along the coast of Hokkaido, waves were about .

Tectonic setting

Japan is situated on a

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

between the Pacific, Philippine Sea,

Okhotsk Okhotsk ( rus, Охотск, p=ɐˈxotsk) is an urban locality (a work settlement) and the administrative center of Okhotsky District of Khabarovsk Krai, Russia, located at the mouth of the Okhota River on the Sea of Okhotsk. Population: ...

and

Amurian Plate The Amur plate (or Amurian plate; also occasionally referred to as the China plate, not to be confused with the Yangtze plate) is a minor tectonic plate in the northern and eastern hemispheres. The Amurian Plate is named after the Amur Rive ...

s. Along the island arc's east and southeast coast,

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 Pacific and Philippine Sea Plates occur at the

Japan Trench The Japan Trench is an oceanic trench part of the Pacific Ring of Fire off northeast Japan. It extends from the Kuril Islands to the northern end of the Izu Islands, and is at its deepest. It links the Kuril–Kamchatka Trench to the north and ...

and

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, ...

, respectively. The Sea of Japan located off Japan's west coast is a back-arc basin which formed from extensional and strike-slip tectonics in the earlt

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

. East–west compression resulted in the formation of

fold and thrust belt A fold and thrust belt is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates outwards ...

s along its eastern margin during the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 This tectonic feature between the Amurian and Okhotsk Plates is thought to be an incipient subduction zone consisting of eastward-dipping

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. I ...

s since no

Wadati–Benioff zone A Wadati–Benioff zone (also Benioff–Wadati zone or Benioff zone or Benioff seismic zone) is a planar zone of seismicity corresponding with the down-going slab in a subduction zone. Differential motion along the zone produces numerous earth ...

is detected. Earthquakes and tsunamis are produced on thrust faults that form the boundary, with magnitudes in the range of 6.8–7.9. Major earthquakes and tsunamis along this boundary occurred in

1833 Events January–March * January 3 – The United Kingdom reasserts British sovereignty over the Falkland Islands in the South Atlantic Ocean. * February 6 (January 25 on the Greek calendar) – Prince Otto Friedrich Ludwig of Bavaria arr ...

1741 Events January–March * January 13 ** Lanesborough, Massachusetts is created as a township. ** Conventicle Act of 1741 is introduced in Denmark-Norway. *February 13 – Sir Robert Walpole, the Prime Minister of Great Britain ...

, 1940,

1964 Events January * January 1 – The Federation of Rhodesia and Nyasaland is dissolved. * January 5 – In the first meeting between leaders of the Roman Catholic and Orthodox churches since the fifteenth century, Pope Paul VI and Patria ...

1983 1983 saw both the official beginning of the Internet and the first mobile cellular telephone call. Events January * January 1 – The migration of the ARPANET to TCP/IP is officially completed (this is considered to be the beginning of the ...

and

1993 The United Nations General Assembly, General Assembly of the United Nations designated 1993 as: * International Year for the World's Indigenous People The year 1993 in the Kwajalein Atoll in the Marshall Islands had only 364 days, since its ...

—the 1741 tsunami was of volcanic origin. These earthquakes suggest deformation is ongoing and are accommodated along these fold and thrust belts.

Earthquake

Seismicity of Eastern margin of the Japan Sea 2

Seismicity along the eastern margin of the Sea of Japan extends from the west coast of

Honshu , historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...

and Hokkaido to

Sakhalin Sakhalin ( rus, Сахали́н, p=səxɐˈlʲin) is an island in Northeast Asia. Its north coast lies off the southeastern coast of Khabarovsk Krai in Russia, while its southern tip lies north of the Japanese island of Hokkaido. An islan ...

in the north. The margin produced several large earthquakes during the 20th century—the 1940

earthquake rupture In seismology, an earthquake rupture is the extent of slip that occurs during an earthquake in the Earth's crust. Earthquakes occur for many reasons that include: landslides, movement of magma in a volcano, the formation of a new fault, or, mos ...

d a segment north of the 1993 event. A

focal mechanism The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...

solution obtained for the 1940 shock corresponded to pure dip-slip (reverse) faulting on a near north–south striking plane.

Seismologist Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

s have interpreted various rupture sizes for the earthquake in studies during the 1960s and 1980s. By using tsunami data, the source areas were × striking north-northwest–south-southeast, and × . These reverse fault planes run parallel to the eastern margin of the Sea of Japan and are steeply-dipping. The earthquake ruptured four faults extending north–south; the Kita-Oshoro, Oshoro, Minami Oshoro and Kaiyo faults. A dive survey around the earthquake source area in the 2000s revealed

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

s of the fold and thrust belt were affected by recent seismic shaking. The Oshoro and Minami Oshoro anticlines (fault underlying the anticline) showed evidence of a recently disturbed seafloor, but no

turbidite A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...

s, indicating the Oshoro and Minami Oshoro faults ruptured during the event. Only the southern portion of the Kita-Oshoro ruptured—the fault may be the northern extent of rupture. Slip along the Oshoro and Minami Oshoro faults were estimated using

seismic inversion In geophysics (primarily in oil-and-gas exploration/development), seismic inversion is the process of transforming seismic reflection data into a quantitative rock-property description of a reservoir. Seismic inversion may be pre- or post- stack, ...

of tsunami waveform at and , respectively. Slip on the Kita-Oshoro and Kaiyo faults were estimated at and , respectively. The

International Seismological Centre The International Seismological Centre (ISC) is a non-governmental, nonprofit organisation charged with the final collection, definitive analysis and publication of global seismicity. The ISC was formed in 1964 as an international organisation ...

catalogued the shock at 7.5 with a depth of . The

Japan Meteorological Agency The Japan Meteorological Agency (JMA; ''気象庁, Kishō-chō'') is a division of the Ministry of Land, Infrastructure, Transport and Tourism dedicated to the Scientific, scientific observation and research of natural phenomena. Headquartered ...

listed the earthquake at 7.5 . Many aftershocks of "very small" magnitudes followed. The aftershock activity decreased with an unusually sudden rate. These were distributed across an estimated -long zone.

Tsunami

The tsunami was generally moderate around Hokkaido and larger at distant places (Korea and Russia). All along the coast of Hokkaido, the tsunami wave was generally under . On

Rishiri Island is a volcanic island in the Sea of Japan off the coast of Hokkaido, Japan. Administratively the island is part of Hokkaido Prefecture, and is divided between two towns, Rishiri and Rishirifuji. The island is formed by the cone-shaped extinct ...

and the port of Tomamae along Hokkaido's west coast, the tsunami measured . A tidal gauge in Iwanai, Hokkaido recorded a tsunami. Along the coast of

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

, waves were observed, while at

Rudnaya Pristan Rudnaya Pristan (, lit. ''Ore Wharf'') is a village ('' selo'') located at the mouth of the Rudnaya River, on the Pacific coast of Primorsky Krai. It is situated 35 km east of Dalnegorsk (also in Primorsky Krai) and approximately 514 km ...

and Kamenka along the

Primorsky Krai Primorsky Krai, informally known as Primorye, is a federal subjects of Russia, federal subject (a krais of Russia, krai) of Russia, part of the Far Eastern Federal District in the Russian Far East. The types of inhabited localities in Russia, ...

coast, waves measured and , respectively.

Damage

130823 Cape Kamui Shakotan Hokkaido Japan01s3

Damage caused by seismic shaking was light;National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information.
doi:10.7289/V5TD9V7K the reported JMA seismic intensities were ''Shindo'' 4 at Haboro and ''Shindo'' 3 at Sapporo, Morimachi, Suttsu, Ishikari-Numata, Asahikawa, and Furano. Shaking was felt across all of western Hokkaido and parts of Russia. Weak shaking was observed at Muroran, Aomori, Mizusawa in

Iwate Prefecture is a Prefectures of Japan, prefecture of Japan located in the Tōhoku region of Honshu. It is the second-largest Japanese prefecture (behind Hokkaido) at , with a population of 1,165,886 (as of July 1, 2023). Iwate Prefecture borders Aomori Pre ...

and Tsukubsan,

Ibaraki Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,828,086 (1 July 2023) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, ...

. The tsunami swept away thousands of fishing boats and timber at Hokkaido, Primorsky Krai and Sakhalin. On the

Shakotan Peninsula The in Shiribeshi, on the west coast of Hokkaidō, Japan, is a mountainous peninsula which projects some into the Sea of Japan. The Shakotan Peninsula forms part of the Niseko-Shakotan-Otaru Kaigan Quasi-National Park. Geography The penin ...

, the waves killed 10 people, destroyed 20 homes, swept away 644 boats, and damaged a further 612.National Geophysical Data Center / World Data Service: NCEI/WDS Global Historical Tsunami Database. NOAA National Centers for Environmental Information.
doi:10.7289/V5PN93H7 The deaths occurred at the

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...

of the

Teshio River The is a river in Hokkaido, Japan. At , it is the second-longest river on the island (after the Ishikari) and the fourth-longest in the country (after the Shinano, Tone, and Ishikari). A Class A river, the Teshio is the northernmost major rive ...

. Twenty four people were injured. At Shiribeshi, a fishing boat sunk and 20 were lost; at Sōya, 550 boats were lost and 189 were destroyed. Fourteen buildings were completely destroyed; another 43 partially ruined at

Rumoi 290px, Rumoi city hall 290px, central Rumoi is a city in Rumoi Subprefecture, Hokkaido, Japan. , the city had an estimated population of 18,132 in 10519 households, and a population density of 61 people per km2. The total area of the city is . T ...

. Fires destroyed 26 buildings and the remaining were destroyed by the tsunami. Seven hundred and twenty one fishing boats were damaged or destroyed; including a motor ship which sunk. Damage in the town was estimated at 260,000 yen. Slight damage occurred on

Sado Island is an island located in the eastern part of the Sea of Japan, under the jurisdiction of Sado City, Niigata Prefecture, Japan, with a coastline of . In October 2017, Sado Island had a population of 55,212 people. Sado Island covers an area of ...

and in northern

, attributed to the tsunami. At Kamenka, the tsunami struck at 01:00 on August 2. It carried three motor torpedo boats inland, where they were dumped on peatland between the Oprichninka and Pryamaya Pad rivers. Large portions of Zarechnaya and Naberezhnaya streets, near the Pryamaya Pad river were flooded. A fish processing factory was flooded at its first level. There were no deaths or injuries associated.

References

{{Earthquakes in Japan Earthquakes in Japan Tsunamis in Japan 1940 earthquakes 1940s tsunamis Floods in North Korea 1940 in Korea August 1940 in Asia 1940 in Russia Tsunamis in Russia

Tectonic setting

Earthquake

Tsunami

Damage

See also

References