The 2003 Hokkaidō earthquake, scientifically named the , occurred off the coast of Hokkaidō, Japan on 26 September at 04:50 local time (19:50 UTC 25 September). At a focal depth of 27 km (17 mi), this

great Great may refer to: Descriptions or measurements * Great, a relative measurement in physical space, see Size * Greatness, being divine, majestic, superior, majestic, or transcendent People * List of people known as "the Great" *Artel Great (born ...

undersea earthquake A submarine, undersea, or underwater earthquake is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean. They are the leading cause of tsunamis. The magnitude can be measured scientifically by the use of the ...

measured 8.3 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pap ...

, making it the most powerful earthquake of 2003, as well as one of the most intense earthquakes to hit Japan since modern record-keeping began in 1900. The Hokkaido earthquake caused extensive damage, destroying roads all around Hokkaidō, and triggered power outages and extensive

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...

s. Over 800 people were injured. The earthquake also caused a tsunami reaching 4 meters in height. The earthquake's presence was felt throughout Japan, stretching all the way to

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island ...

and

Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...

Tectonic setting

The location and

moment tensor solution The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

of this earthquake are consistent with it being a result of

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

ing between the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacifi ...

and the subducting

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and I ...

. In addition to experiencing large thrust earthquakes that originate on the interface between the plates, eastern Hokkaidō experiences great earthquakes that originate from the interior of the subducted Pacific plate. The region experienced a catastrophic earthquake and tsunami with an estimated magnitude of 9 in 1667, a magnitude 8.2 event in 1952, a 1968 quake measuring 8.3 , and one in 2008 measuring 7.1, all bearing the name ''Tokachi-Oki'', and a 1973 quake to the immediate north along the

Kuril Trench The Kuril Islands or Kurile Islands (; rus, Кури́льские острова́, r=Kuril'skiye ostrova, p=kʊˈrʲilʲskʲɪjə ɐstrɐˈva; Japanese: or ) are a volcanic archipelago currently administered as part of Sakhalin Oblast in the ...

plate boundary called the

1973 Nemuro earthquake The in scientific literature, occurred on June 17 at 12:55 local time. It struck with an epicenter just off the Nemuro Peninsula in northern Hokkaidō, Japan. It measured 7.8–7.9 on the moment magnitude scale (), 8.1 on the tsunami magnitud ...

Aftershocks

As of 3 October 2003, a total of 65 aftershocks were reported near the main shock

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

. At least one major tremor occurred, measuring magnitude 7.0 on the

Richter scale The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 p ...

. At the time, specialists assessed a 50% probability of an aftershock of magnitude 6.0 or greater to occur within the subsequent 72 hours, with a 20% chance of its magnitude exceeding 7.0.

Damage and casualties

Despite the earthquake's great intensity, structural damage to the region was comparatively light; the epicenter was located nearly a hundred kilometers offshore, with most structures in its vicinity reported to be resistant to earthquake shaking. The majority of the destruction was confined to coastal areas, such as sea and fishing ports, mostly inflicted by subsequent tsunami waves. Although

soil liquefaction Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, ...

was observed over a broad geological area, it occurred in localized areas almost exclusively limited to man-made embankments. The earthquake affected a total of 36 local rivers, including the major

Abashiri is a city located in Okhotsk Subprefecture, Hokkaido, Japan. Abashiri is known as the site of the Abashiri Prison, a Meiji-era facility used for the incarceration of political prisoners. The old prison has been turned into a museum, but the ci ...

and

Ishikari River The , at long, is the third longest in Japan and the longest in Hokkaidō. The river drains an area of , making it the second largest in Japan, with a total discharge of around per year. It originates from Mount Ishikari in the Daisetsuzan ...

s. Many properties received considerable damage, two individuals remain missing and 849 people sustained injuries. Monetary losses in Hokkaido amounted to at least ¥213 billion (2003 JPY), or $1.9 billion (2003

USD The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...

). One person died after being hit by a car after cleaning up earthquake damage.

Structures

The earthquake and its associated tsunami waves destroyed several oceanside home communities and damaged many others. Over 1,500 houses or buildings – the majority of which were in Kushiro city – suffered considerable damage, with of a total of 141 reported to be partially or completely destroyed. Strong shaking affected many bridges in the region, some sustaining severe damage due to relative motion between spans in excess of design standards. The center of the Rekifune Bridge, located in Taiki, Hiroo, was reported to have sunk about 0.12 m (0.39 ft) at the joint section following significant ground deformation. Some local schools were also damaged, ranging from shattered windows to severed

expansion joint An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...

s and columns. Two town halls in Kushiro and Taiku suffered partial collapses. At

Kushiro Airport is an airport in Japan, located west northwestAIS Japan
of

, the tremor caused the control tower ceiling to collapse, prompting officials to halt control work for several days. Small cracks were reported in the gates of the Takami Hokkaidō Dam, though no threat of

dam failure A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than ...

existed.

Harbour facilities

Several sea ports in the area sustained moderate damage – such as cracks and wall collapse – due to lateral ground spreading caused by liquefaction. Some 123 coastal fishing ports and facilities in eastern Hokkaidō reported significant damage, with an additional 25 ports damaged in Iwate. At least three major ports were affected by the disaster;

Kushiro is a Cities of Japan, city in Kushiro Subprefecture on the island of Hokkaido, Japan. It serves as the subprefecture's capital and it is the most populated city in the eastern part of the island. Geography Mountains * Mount Oakan * Mount Mea ...

Port sustained great damage to one of its piers as a result of ground displacement and

sand boil Sand boils or sand volcanoes occur when water under pressure wells up through a bed of sand. The water looks like it is boiling up from the bed of sand, hence the name. Sand volcano A sand volcano or sand blow is a cone of sand formed by the ...

s. Tsunami waves stranded several small boats onshore; various ship containers and oil tanks along coastlines sustained damage. The earthquake left marine oil spills in its wake, though the conditions were quickly normalized.

References

External links

* * {{DEFAULTSORT:2003 Hokkaido Earthquake Hokkaido Earthquake, 2003 Hokkaido Earthquake, 2003 Earthquakes of the Heisei period Megathrust earthquakes in Japan 2003 tsunamis September 2003 events in Japan Landslides in Japan 2003 disasters in Japan