869 Sanriku earthquake and tsunami
Encyclopedia
The struck the area around Sendai in the northern part of Honshu
on 9 July 869 (May 26,
Jōgan
11). The earthquake
had an estimated magnitude of 8.6 on the surface wave magnitude
scale. The tsunami caused widespread flooding of the Sendai plain, with sand deposits being found up to 4 kilometres (2.5 mi) from the coast.
is a historical name for an area corresponding to today's Aomori
, Iwate
and parts of Miyagi Prefecture
. The earthquake is also known as the in Japanese, where Jōgan is the Japanese era name
for the period from 859 to 877.
The Japanese history text, Nihon Sandai Jitsuroku
which was compiled in 901, recorded the 869 earthquake and tsunami of Mutsu Province
.
between the over-riding Okhotsk Plate
(a proposed microplate within the North American Plate
) and the subducting
Pacific Plate
. This boundary has been associated with a series of large historical earthquakes, originating either from rupture along the plate interface or from deformation within either the over-riding or subducting plates, many of them triggering a destructive tsunami, such as the 1896 Meiji-Sanriku earthquake
.
of the Tōhoku region
, Emishi
, at that time. According to Nihon Sandai Jitsuroku, around 1000 people were killed by the tsunami.
Despite a lack of reliable sources, there are legends about the earthquake from Tōhoku region to Bōsō Peninsula
.
The tsunami caused extensive flooding of the Sendai plain, destroying the town of Tagajō
. Archaeological investigations have identified the remains of 8th and 9th century buildings beneath the town, covered by sediments dated to the middle of the 10th century.
suggests that the extent of sand deposition in the earlier events underestimated the degree of inundation. A muddy deposit was found to extend half as far again as the sand sheet. As the topography and cultivation of the Sendai plain has not changed significantly since 869, it has been proposed that the sources of the 2011 and 869 tsunamis were of comparable size, suggesting that the magnitude of the 869 earthquake has been underestimated.
sequence of the Sendai plain, all formed within the last 3,000 years, suggesting an 800 to 1,100 year recurrence interval for large tsunamigenic earthquakes. In 2001 it was reckoned that there was a high likelihood of a large tsunami hitting the Sendai plain as more than 1,100 years had then elapsed.
As for the other two large tsunamis recognized before the 869 tsunami, one was estimated to have occurred between about 1000 BC and 500 BC and the other around 1 AD. In 2007 the probability of an earthquake with a magnitude of Mw 8.1–8.3 was estimated as 99% within the following 30 years.
The 2011 Tōhoku earthquake was somewhat larger than the predicted event, but occurred in the same area as the 869 earthquake and caused major flooding in the Sendai area.
Honshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...
on 9 July 869 (May 26,
Jōgan
Jogan
was a after Ten'an and before Gangyō. This period spanned the years from April 859 through April 877. The two reigning emperors were and .-Change of era:* February 7, 859 : The new era name was created to mark an event or series of events...
11). The earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
had an estimated magnitude of 8.6 on the surface wave magnitude
Surface wave magnitude
The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost layers of the earth...
scale. The tsunami caused widespread flooding of the Sendai plain, with sand deposits being found up to 4 kilometres (2.5 mi) from the coast.
Name
SanrikuSanriku
is a historical region of Japan on the northeastern side of the island of Honshu, corresponding to today's Aomori, Iwate and parts of Miyagi Prefecture...
is a historical name for an area corresponding to today's Aomori
Aomori Prefecture
is a prefecture of Japan located in the Tōhoku Region. The capital is the city of Aomori.- History :Until the Meiji Restoration, the area of Aomori prefecture was known as Mutsu Province....
, Iwate
Iwate Prefecture
is the second largest prefecture of Japan after Hokkaido. It is located in the Tōhoku region of Honshū island and contains the island's easternmost point. The capital is Morioka. Iwate has the lowest population density of any prefecture outside Hokkaido...
and parts of Miyagi Prefecture
Miyagi Prefecture
is a prefecture of Japan in the Tōhoku Region on Honshu island. The capital is Sendai.- History :Miyagi Prefecture was formerly part of the province of Mutsu. Mutsu Province, on northern Honshu, was one of the last provinces to be formed as land was taken from the indigenous Emishi, and became the...
. The earthquake is also known as the in Japanese, where Jōgan is the Japanese era name
Japanese era name
The Japanese era calendar scheme is a common calendar scheme used in Japan, which identifies a year by the combination of the and the year number within the era...
for the period from 859 to 877.
The Japanese history text, Nihon Sandai Jitsuroku
Nihon Sandai Jitsuroku
, abbreviated as Sandai Jitsuroku, is an officially commissioned Japanese history text. Completed in 901, it is the sixth and final text in the Six National Histories series. It covers the years 858-887.-Background:...
which was compiled in 901, recorded the 869 earthquake and tsunami of Mutsu Province
Mutsu Province
was an old province of Japan in the area of Fukushima, Miyagi, Iwate and Aomori prefecture and the municipalities of Kazuno and Kosaka in Akita Prefecture...
.
Tectonic setting
The northern part of Honshu lies above the convergent boundaryConvergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
between the over-riding Okhotsk Plate
Okhotsk Plate
The Okhotsk Plate is a tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the...
(a proposed microplate within the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
) and the subducting
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
. This boundary has been associated with a series of large historical earthquakes, originating either from rupture along the plate interface or from deformation within either the over-riding or subducting plates, many of them triggering a destructive tsunami, such as the 1896 Meiji-Sanriku earthquake
1896 Meiji-Sanriku earthquake
The 1896 Meiji-Sanriku earthquake was highly destructive, generating one of the most devastating tsunamis in Japanese history, destroying about 9,000 homes and causing at least 22,000 deaths. This magnitude 7.2 event occurred at 19:32 on June 15, 1896...
.
Damage
In the area which the earthquake struck, the Imperial Court of Japan battled with an indigenous peopleIndigenous peoples
Indigenous peoples are ethnic groups that are defined as indigenous according to one of the various definitions of the term, there is no universally accepted definition but most of which carry connotations of being the "original inhabitants" of a territory....
of the Tōhoku region
Tohoku region
The is a geographical area of Japan. The region occupies the northeastern portion of Honshu, the largest island of Japan. The region consists of six prefectures : Akita, Aomori, Fukushima, Iwate, Miyagi and Yamagata....
, Emishi
Emishi
The constituted a group of people who lived in northeastern Honshū in the Tōhoku region. They are referred to as in contemporary sources. Some Emishi tribes resisted the rule of the Japanese Emperors during the late Nara and early Heian periods...
, at that time. According to Nihon Sandai Jitsuroku, around 1000 people were killed by the tsunami.
Despite a lack of reliable sources, there are legends about the earthquake from Tōhoku region to Bōsō Peninsula
Boso Peninsula
thumb|Locationthumb|Landsat image with high-resolution data from Space Shuttle is a peninsula in Chiba prefecture on Honshū, the largest island of Japan. It forms the eastern edge of Tokyo Bay, separating it from the Pacific Ocean....
.
The tsunami caused extensive flooding of the Sendai plain, destroying the town of Tagajō
Tagajo, Miyagi
is a city located in Miyagi Prefecture, Japan.The city was named after Taga Castle, the capital of Mutsu Province.As of 2010, the city has an estimated population of 63,256 and the population density of 3,220 persons per km². The total area is 19.64 km²....
. Archaeological investigations have identified the remains of 8th and 9th century buildings beneath the town, covered by sediments dated to the middle of the 10th century.
Earthquake
The estimated magnitude of the earthquake as 8.6 on the surface wave magnitude scale, has been taken from modelling of the tsunami. A source area of 200 kilometres (124.3 mi) long by 85 kilometres (52.8 mi) wide with a displacement of 2 metres (6.6 ft) is consistent with the observed distribution and degree of flooding. Analysis of the tsunami deposits associated with the 2011 earthquake2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...
suggests that the extent of sand deposition in the earlier events underestimated the degree of inundation. A muddy deposit was found to extend half as far again as the sand sheet. As the topography and cultivation of the Sendai plain has not changed significantly since 869, it has been proposed that the sources of the 2011 and 869 tsunamis were of comparable size, suggesting that the magnitude of the 869 earthquake has been underestimated.
Tsunami
The extent of flooding caused by the tsunami of the Sendai plain has been mapped using dated deposits of sand. The tsunami flooded at least 4 kilometres (2.5 mi) inland.Predicted earthquake hazard
Three tsunami deposits have been identified within the HoloceneHolocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
sequence of the Sendai plain, all formed within the last 3,000 years, suggesting an 800 to 1,100 year recurrence interval for large tsunamigenic earthquakes. In 2001 it was reckoned that there was a high likelihood of a large tsunami hitting the Sendai plain as more than 1,100 years had then elapsed.
As for the other two large tsunamis recognized before the 869 tsunami, one was estimated to have occurred between about 1000 BC and 500 BC and the other around 1 AD. In 2007 the probability of an earthquake with a magnitude of Mw 8.1–8.3 was estimated as 99% within the following 30 years.
The 2011 Tōhoku earthquake was somewhat larger than the predicted event, but occurred in the same area as the 869 earthquake and caused major flooding in the Sendai area.
See also
- Seismicity of the Sanriku coast
- 1896 Meiji-Sanriku earthquake1896 Meiji-Sanriku earthquakeThe 1896 Meiji-Sanriku earthquake was highly destructive, generating one of the most devastating tsunamis in Japanese history, destroying about 9,000 homes and causing at least 22,000 deaths. This magnitude 7.2 event occurred at 19:32 on June 15, 1896...
- 1933 Sanriku earthquake1933 Sanriku earthquakeThe was a major earthquake whose associated tsunami caused widespread damage to towns on the Sanriku coast of the Tōhoku region of Honshū, Japan on March 2, 1933.-History:The epicenter of the 1933 Sanriku earthquake was located offshore,...
- 2011 Tōhoku earthquake
- 1896 Meiji-Sanriku earthquake