The occurred at 17:14 local time (08:14 UTC) on 12 June. The epicentre was offshore of Miyagi Prefecture, Japan. It had a surface wave magnitude of 7.7, JMA magnitude 7.4, and triggered a small

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

. The earthquake reached a maximum intensity of Shindo 5 in Sendai and caused 28 deaths and 1,325 injuries.

Geology

The northeastern part of Honshū lies above the subduction zone that forms 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 ...

, where the Pacific Plate is being subducted beneath the

Okhotsk Plate The Okhotsk Plate is a minor tectonic plate covering the Kamchatka Peninsula, Magadan Oblast, and Sakhalin Island of Russia; Hokkaido, Kantō and Tōhoku regions of Japan; the Sea of Okhotsk, as well as the disputed Kuril Islands. It was ...

. The rupture of the plate interface that caused the earthquake, occurred in two distinct stages, from study of surface and body wave data and the distribution of aftershocks. The first stage of rupture propagated northwards, roughly parallel to the trench axis, along the upper of the two aftershock zones. The second stage began after about 11 seconds with a second shock, about 30 km westward of the first, at the base of the upper aftershock zone, propagating down dip. The cause of this rupture sequence is thought to be the presence of a barrier, a zone of higher strength, between the two aftershock zones. Earthquakes with similar magnitudes have occurred in this region periodically, about every 40 years. Such earthquakes include the ones that occurred in 1793, 1835, 1861, 1897, 1936, and 1978. The

2005 Miyagi earthquake On 16 August 2005, an earthquake struck the east coast of the Japanese island of Honshū at 11.46 am (02:46 UTC) on 16 August 2005, causing damage and power outages. The event registered 7.2 on the moment magnitude scale. Earthquake char ...

is not considered to be the one that was expected to follow the 1978 Miyagi earthquake. More recent comparisons have confirmed the differences between the 1978 and 2005 events but called into question whether this sequence truly represents the repeat of a

characteristic earthquake Earthquake prediction is a branch of the science of seismology concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits, and particularly "the determination of parameters for the ''next'' ...

. The rupture zone of the 1978 earthquake occurred at the westernmost limit of known interplate earthquakes, some 150 km back from the trench. This deepest part of the rupture zone, about 40 km, is interpreted to represent the depth of transition to

aseismic creep In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip in ...

on the plate interface. The maximum

peak ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a par ...

recorded was 0.125g. There was a foreshock of magnitude M_j 5.8 at 17:06 local time, minutes before the main shock.

Damage

There were widespread landslides that caused extensive damage to highways and one death in the area around Sendai. 1,183 houses were completely destroyed within Miyagi Prefecture, with a further 5,574 partially destroyed. Soil liquefaction was observed in lands claimed by embankment. No damage was reported from the tsunami.

Tsunami

A maximum wave height of about was recorded at

Kesennuma is a city in Miyagi Prefecture, Japan. , the city had an estimated population of 59,803 and a population density of in 26,390 households. The total area of the city is . Large sections of the city were destroyed by the 2011 Tōhoku earthquake an ...

and Onagawa, close to the epicenter.

Aftermath

The extent of damage to buildings caused by the earthquake, led directly to a revision of the Japanese Building Standard Act in 1981. The earthquake also led to a major revision in the Earthquake Insurance System, which had been set up by the Japanese government in 1966.

2011 Tōhoku earthquake and tsunami

As of March 2011 it is not known if the

2011 Tōhoku earthquake and tsunami The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude 9.0–9.1 (M) undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region, and lasted approximately six mi ...

is related to the 1978 Miyagi quake periodic sequence. Some involved geological research will be required to see if there is a relationship between the quake events. Notable linkages * The time difference between the quakes is 33 years – a number that is within the probability for being related to the 1978 Miyagi quake sequence. * There are some suggestions that the 2011 Tōhoku quake is part of a 1000-year sequence (that is not related to the 40-year Miyagi quake sequence) as a similar quake and tsunami hit the Sendai coast in 869 AD.

References

External links

* {{JapanTrenchMegathrust Miyagi earthquake Miyagi earthquake Miyagi earthquake Miyagi earthquake History of Miyagi Prefecture Earthquakes of the Showa period Landslides in Japan Miyagi earthquake