1896 Meiji-Sanriku earthquake
Encyclopedia
The 1896 Meiji-Sanriku earthquake was highly destructive, generating one of the most 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...

s in Japanese history, destroying about 9,000 homes and causing at least 22,000 deaths. This 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...

 7.2 event occurred at 19:32 (local time) on June 15, 1896. The magnitude of the tsunami (Mt = 8.2) was much greater than expected for the estimated seismic magnitude and this earthquake has been regarded as being part of a distinct class of events, 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...

.

Background

The epicenter of this earthquake lies just to the west of the Japan Trench
Japan Trench
__notoc__The Japan Trench is an oceanic trench, a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. It extends from the Kuril Islands to the Bonin Islands and is at its deepest. It is an extension of the Kuril-Kamchatka Trench to the north and the...

, the surface expression of the west-dipping 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"...

 zone that forms part of the convergent boundary
Convergent 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 Pacific
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....

 and Eurasian
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...

 plates.

Characteristics

The unusual disparity between the magnitudes of tsunami and earthquake in such an event has led to two possible explanations;
  • The tsunami was caused by a slope failure triggered by the earthquake
  • The rupture velocity was unusually low


Tanioka and Sataka (1996) proposed that in this case the effect of subducted sediment beneath the accretionary wedge
Accretionary wedge
An accretionary wedge or accretionary prism is formed from sediments that are accreted onto the non-subducting tectonic plate at a convergent plate boundary...

 was responsible for a slow rupture velocity. They modelled the effects of a 20° dipping fault along the top of the subducting plate and found that they could match both the observed seismic response and tsunami, but required a displacement of 10.4 m. The displacement can be reduced to a more reasonable value by considering the extra uplift caused by the deformation of sediments in the wedge and a shallower fault dip of 10°. This revised fault model gives a magnitude
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

 of Mw=8.0-8.1, much closer to the estimated tsunami magnitude. A magnitude of 8.5 on the moment magnitude scale
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

 has also been estimated for this event.

Tsunami

At 7:30 pm on June 15, 1896, families were celebrating the return of soldiers from the First Sino-Japanese War
First Sino-Japanese War
The First Sino-Japanese War was fought between Qing Dynasty China and Meiji Japan, primarily over control of Korea...

 and a Shinto
Shinto
or Shintoism, also kami-no-michi, is the indigenous spirituality of Japan and the Japanese people. It is a set of practices, to be carried out diligently, to establish a connection between present day Japan and its ancient past. Shinto practices were first recorded and codified in the written...

 holiday when they felt a small earthquake. There was little concern because it was so weak and there had been many small tremors in the previous few months. About 35 minutes later the Sanriku coast
Sanriku Coast
The is a coastal region on the Pacific Ocean, extending from southern Aomori prefecture, through Iwate prefecture and northern Miyagi prefecture in northeastern Honshū, which is Japan's main island...

 was struck by the first wave of the tsunami, followed by a second a few minutes later. The tsunami damage was particularly severe because it coincided with high tide. Wave heights of up to 38.2 metres (125.3 ft) were measured. Nearly 9,000 homes were destroyed and 22,066 deaths were recorded. Most deaths occurred in Iwate and Miyagi
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...

, although casualties were also recorded from 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....

 and Hokkaido
Hokkaido
, formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island; it is also the largest and northernmost of Japan's 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaido from Honshu, although the two islands are connected by the underwater railway Seikan Tunnel...

. An unusual number of the victims were found with fractured skulls and limbs either broken or missing, testifying to the power of the tsunami. As was their normal practice each evening, the local fishing fleets were all at sea when the earthquake struck. In the deep water the wave went unnoticed, and when they returned the next morning they found themselves sailing amongst a mass of debris and bodies.

The tsunami also caused damage in Hawaii where wharves were destroyed and several houses swept away, wave heights of up to 9 metres (29.5 ft) were measured.

Aftermath

No attempt was made after this tsunami to establish preventative measures against similar events in the future and it was not until after the tsunami caused by the 1933 Sanriku earthquake
1933 Sanriku earthquake
The 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,...

 that the local government took such action. But higher levels of tsunami awareness resulted in lighter losses in the 1933 tsunami. However, the earthquake of 11 March 2011
2011 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...

, which was of far higher magnitude than those of 1896 and 1933, caused a huge tsunami that resulted in thousands of deaths across the same region.

See also

  • Seismicity of the Sanriku coast
    • 869 Sanriku earthquake
      869 Sanriku earthquake and tsunami
      The struck the area around Sendai in the northern part of Honshu on 9 July 869 . The earthquake had an estimated magnitude of 8.6 on the surface wave magnitude scale...

    • 1933 Sanriku earthquake
      1933 Sanriku earthquake
      The 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
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