The 2003 Hokkaidō earthquake, scientifically named the , occurred off the coast of

Hokkaidō is the second-largest island of Japan and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by railway via the Seikan Tunnel. The ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

on 26 September at 04:50 local time (19:50

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

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 (bo ...

undersea earthquake measured 8.3 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mwg, 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. was defined in a 1979 paper ...

, 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, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

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

Honshu , historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...

and

Tokyo Tokyo, officially the Tokyo Metropolis, is the capital of Japan, capital and List of cities in Japan, most populous city in Japan. With a population of over 14 million in the city proper in 2023, it is List of largest cities, one of the most ...

Tectonic setting

The location and moment tensor solution 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. I ...

ing between the North American plate and the subducting Pacific plate. 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 a few decades before 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 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 magnitude s ...

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. Determination The primary purpose of a ...

. 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 Richter in collaboration with Beno Gutenberg, and pr ...

. 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 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 Shear strength (soil), strength and stiffness in response to an applied Shear stress, stress such as shaking during an earthquake or other s ...

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 ...

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: $; currency code: USD) is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it int ...

). 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 A expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials. They are commonly found between sections of buildings, bridges, s ...

s and columns. Two town halls in Kushiro and Taiku suffered partial collapses. At Kushiro Airport, 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 city in Kushiro Subprefecture on the island of Hokkaido, Japan. Located along the coast of the North Pacific Ocean, it serves as the subprefecture's capital and it is the most populated city in the eastern part of the island. History An ...

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

sand boil Sand boils, sand volcanoes, or sand blows 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 ...

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 Earthquakes of the Heisei era Megathrust earthquakes in Japan 2003 tsunamis September 2003 in Japan Landslides in Japan 2003 disasters in Japan