1605 Keichō Nankaidō earthquake
Encyclopedia
The 1605 Keichō Nankaidō earthquake occurred at about 20:00 local time on 3 February. It had an estimated magnitude of 7.9 on the surface wave magnitude
scale and triggered a devastating tsunami
that resulted in thousands of deaths in the Nankai and Tōkai
regions of Japan
. It is uncertain whether there were two separate earthquakes separated by a short time interval or a single event. It is referred to as a tsunami earthquake
, in that the size of the tsunami greatly exceeds that expected from the magnitude of the earthquake.
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, the segments have ruptured either singly or together repeatedly over the last 1,300 years. Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them although in the 1707 Hōei earthquake
all segments are thought to have ruptured at once. In 1854 there were two earthquakes a day apart and there were similar earthquakes in 1944 and 1946. In each case, the northeastern segment ruptured before the southwestern segment. In the 1605 event, there is evidence for two distinct earthquakes, but they are not distinguished by all historical sources and some seismologists suggest that only the Nankai segment of the megathrust ruptured.
where they can be compared. The regional extent of this tsunami is supported by the discovery of tsunami deposit
s on the northeastern part of the Kii Peninsula
and at Lake Hamana
correlated to this event. Victims of the tsunami were also reported from Kyushu
.
and 80 at Arai
. Castles were reported destroyed at Tawara in Atsumi and Kakegawa
. The total number of casualties is uncertain as records are incomplete and contradictory, but estimates are in the order of thousands.
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 and triggered a devastating tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
that resulted in thousands of deaths in the Nankai and Tōkai
Tokai region
The is a sub-region of the Chūbu region in Japan that runs along the Pacific Ocean. The name means "East sea" and comes from the Tōkaidō, one of the Edo Five Routes...
regions of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. It is uncertain whether there were two separate earthquakes separated by a short time interval or a single event. It is referred to as a tsunami earthquake
Tsunami earthquake
A tsunami earthquake is an earthquake that triggers a tsunami of a magnitude that is very much larger than the magnitude of the earthquake as measured by shorter-period seismic waves. The term was introduced by Hiroo Kanamori in 1972. Such events are a result of relatively slow rupture velocities...
, in that the size of the tsunami greatly exceeds that expected from the magnitude of the earthquake.
Background
The southern coast of HonshuHonshu
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...
runs parallel to the Nankai Trough
Nankai Trough
The Nankai Trough is a submarine trough located south of Japan's island of Honshū, extending approximately 900 km offshore. In plate tectonics, the Nankai Trough marks a subduction zone that is caused by subduction of the Philippine Sea Plate beneath Japan, part of the Eurasian plate...
, which marks the subduction
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"...
of the Philippine Sea Plate beneath the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
. Movement on this convergent plate boundary leads to many earthquakes, some of them of megathrust type
Megathrust earthquake
Megathrust earthquakes occur at subduction zones at destructive plate boundaries , where one tectonic plate is forced under another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes ...
. 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 1,300 years. Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them although in the 1707 Hōei earthquake
1707 Hōei earthquake
The 1707 Hōei earthquake, which occurred at 14:00 local time on October 28, 1707, was the largest in Japanese history until the 2011 Tōhoku earthquake surpassed it. It caused moderate to severe damage throughout southwestern Honshu, Shikoku and southeastern Kyūshū. The earthquake and the resulting...
all segments are thought to have ruptured at once. In 1854 there were two earthquakes a day apart and there were similar earthquakes in 1944 and 1946. In each case, the northeastern segment ruptured before the southwestern segment. In the 1605 event, there is evidence for two distinct earthquakes, but they are not distinguished by all historical sources and some seismologists suggest that only the Nankai segment of the megathrust ruptured.
Earthquake
There are very few reports of shaking associated with this earthquake, with most historical records only mentioning the tsunami. This has led seismologists to interpret this as a 'tsunami earthquake', probably involving a slow rupture velocity causing little observed shaking while generating a large tsunami.Tsunami
The records of this tsunami are quite sparse but the maximum wave heights are larger than those for either the 1707 Hōei or 1854 Ansei Nankai tsunamis in areas on the south coast of ShikokuShikoku
is the smallest and least populous of the four main islands of Japan, located south of Honshū and east of the island of Kyūshū. Its ancient names include Iyo-no-futana-shima , Iyo-shima , and Futana-shima...
where they can be compared. The regional extent of this tsunami is supported by the discovery of tsunami deposit
Tsunami deposit
A tsunami deposit is a sedimentary unit deposited as the result of of a tsunami. Such deposits may be left onshore during the inundation phase or offshore during the 'backwash' phase. Such deposits are being used to identify past tsunami events and thereby better constrain estimates of both...
s on the northeastern part of the Kii Peninsula
Kii Peninsula
The is the largest peninsula on the island of Honshū in Japan. The area south of the “Central Tectonic Line” is called Nankii , and includes the most poleward living coral reefs in the world due to the presence of the warm Kuroshio Current, though these are threatened by global warming and human...
and at Lake Hamana
Lake Hamana
in Shizuoka Prefecture is Japan's tenth largest lake . It spans the boundaries of the cities of Hamamatsu and Kosai.-Data:The lake has an area of 65.0 km² and holds 0.35 km³ of water. Its circumference is 114 km. At its deepest point, the water is 16.6 m deep...
correlated to this event. Victims of the tsunami were also reported from Kyushu
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....
.
Damage
There is no reported damage associated with the earthquake itself. 700 houses were reported washed away at HiroHirogawa, Wakayama
is a town located in Arida District, Wakayama, Japan.As of 2003, the town has an estimated population of 8,221 and a density of 125.80 persons per km²...
and 80 at Arai
Arai, Shizuoka
is a former town located in Hamana District, Shizuoka, Japan. As of March 31, 2010, the town had an estimated population of 16,975 and a population density of 910 persons per km². The total area was 18.65 km².-Geography:...
. Castles were reported destroyed at Tawara in Atsumi and Kakegawa
Kakegawa Castle
is a hirayama-style Japanese castle. It was the seat of various fudai daimyō who ruled over Kakegawa Domain, Tōtōmi Province, in what is now central Kakegawa, Shizuoka Prefecture, Japan.-History:...
. The total number of casualties is uncertain as records are incomplete and contradictory, but estimates are in the order of thousands.