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The 1896 Meiji-Sanriku earthquake was highly destructive, generating the most devastating tsunami in Japanese history, destroying about 9,000 homes and causing at least 22,000 deaths. This magnitude 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.

Background

The epicenter of this earthquake lies just to the west of the Japan Trenchmarker, the surface expression of the west-dipping subduction zone that forms part of the convergent boundary between the Pacific and Eurasian 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 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 of Mw=8.0-8.1, much closer to the estimated tsunami magnitude.

Tsunami

At 7:30 pm on June 15, families were celebrating the return of soldiers from the Sino Japanese War and a Shinto 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 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 were measured. Nearly 9,000 homes were destroyed and 22,066 deaths were recorded. Most deaths occurred in Iwate and Miyagimarker, although casualties were also recorded from Aomorimarker and Hokkaidomarker. 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 Hawaiimarker where wharves were destroyed and several houses swept away, wave heights of up to 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 earthquakemarker that the local government took such action.

See also



References


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