1978 Miyagi earthquake
Encyclopedia
The occurred at 17:14 local time (08:14 UTC) on 12 June. It had a magnitude
of 7.7, JMA magnitude 7.4, and triggered a small tsunami
. The earthquake
reached a maximum intensity of Shindo 5
in Sendai and caused 28 deaths and 1,325 injuries.
lies above the subduction
zone that forms the Japan Trench
, where the Pacific Plate
is being subducted beneath the Okhotsk Plate
.
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
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.
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
on the plate interface.
The maximum peak ground acceleration
recorded was 0.125g
s that caused extensive damage to highways and 1 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.
and Onagawa, close to the epicenter.
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
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...
of 7.7, JMA magnitude 7.4, and triggered a small 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...
. 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...
reached a maximum intensity of Shindo 5
Japan Meteorological Agency seismic intensity scale
The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan and Taiwan to measure the intensity of earthquakes. It is measured in units of...
in Sendai and caused 28 deaths and 1,325 injuries.
Geology
The northeastern part of HonshūHonshu
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...
lies above 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"...
zone that forms 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...
, where the 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....
is being subducted beneath the 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...
.
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
2005 Miyagi earthquake
The 2005 Miyagi earthquake was a powerful earthquake that struck the east coast of the Japanese island of Honshū at 11.46am on August 16, causing casualties, building collapses and power outages.-Earthquake characteristics:...
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.
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
Aseismic creep
In geology, aseismic creep is measurable surface displacement along a fault in the absence of notable earthquakes.An example is along the Calaveras fault in Hollister, California. Streets crossing the fault in Hollister show significant offset and several houses sitting atop the fault are notably...
on the plate interface.
The maximum peak ground acceleration
Peak ground acceleration
Peak ground acceleration is a measure of earthquake acceleration on the ground and an important input parameter for earthquake engineering, also known as the design basis earthquake ground motion...
recorded was 0.125g
Damage
There were widespread landslideLandslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s that caused extensive damage to highways and 1 death in the area around Sendai. 1,183 houses were completely destroyed within Miyagi Prefecture, with a further 5,574 partially destroyed. Soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
was observed in lands claimed by embankment. No damage was reported from the tsunami.
Tsunami
A maximum wave height of about 60 cm (23.6 in) was recorded at KesennumaKesennuma, Miyagi
is a city located in the extreme northeast of Miyagi Prefecture, Japan, founded on June 1, 1953. It wraps around the western part of Kesennuma Bay, and also includes the island of Ōshima...
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 tsunami2011 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...
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 not related to the 40 year Miyagi quake sequence) as a similar quake and tsunami hit the Sendai coast in 869 AD869 Sanriku earthquake and tsunamiThe 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...
.