1995 Hanshin earthquake

At least 5,000 people died, around 4,600 of them from Kobe. Kobe, with its population of 1.5 million, was the closest major city to the epicenter and hit by the strongest tremors. It was Japan's second deadliest earthquake in the 20th century after the 1923 Great Kantō earthquake, in which more than 105,000 people died.

Earthquake

Most of the largest earthquakes in Japan are caused by subduction of the Philippine Sea plate or Pacific plate, with mechanisms that involve either energy released within the subducting plate or the accumulation and sudden release of stress in the overlying plate. Earthquakes of these types are especially frequent in the coastal regions of northeastern Japan.

The Great Hanshin earthquake belonged to a third type, called an "inland shallow earthquake". Earthquakes of this type occur along active faults. Even at lower magnitudes, they can be very destructive because they often occur near populated areas and because their hypocenters are located less than 20 km below the surface. The Great Hanshin earthquake began north of the island of Awaji, which lies just south of Kobe. It spread toward the southwest along the Nojima Fault on Awaji and toward the northeast along the Suma and Suwayama faults, which run through the center of Kobe. Observations of deformations in these faults suggest that the area was subjected to east–west compression, which is consistent with previously known crustal movements. Like other earthquakes recorded in western Japan between 1891 and 1948, the 1995 earthquake had a strike-slip mechanism that accommodated east–west shortening of the Eurasian plate due to its collision with the Philippine Sea plate in central Honshu.

The Mj 7.3 earthquake struck at 05:46:53 JST on the morning of January 17, 1995. It lasted for 20 seconds. During this time the south side of the Nojima Fault moved 1.5 meters to the right and 1.2 meters downwards. There were four foreshocks, beginning with the largest (Mj 3.7) at 18:28 on the previous day.

Intensity

It was the first time that an earthquake in Japan was officially measured at a seismic intensity (shindo in Japanese) of the highest Level 7 on the scale of Japan Meteorological Agency (JMA). After the earthquake, seismic intensity observation in Japan was fully mechanized (from April 1996) and JMA seismic intensity Levels 5 and 6 were each divided into 2 levels (from October 1996).

An on-the spot investigation by JMA concluded that tremors by this earthquake were at seismic intensity of Level 7 in particular areas in northern Awaji Island (now Awaji City) and in the cities of Kobe, Ashiya, Nishinomiya and Takarazuka.

Tremors were valued at seismic intensity of Levels 4 to 6 at observation points in Kansai, Chūgoku, Shikoku and Chūbu regions:

Damage

Damage was widespread and severe. Structures irreparably damaged by the earthquake included nearly 400,000 buildings, numerous elevated road and rail bridges, and 120 of the 150 quays in the port of Kobe. The quake triggered approximately 300 fires, which raged over large portions of the city. Disruptions of water, electricity and gas supplies were common. Residents feared returning home because of aftershocks that lasted several days (74 of which were strong enough to be felt).

The majority of deaths (over 4,000) occurred in cities and suburbs in Hyōgo Prefecture. A total of 68 children under the age of 18 were orphaned, while 332 children lost one parent.

One in five of the buildings in the worst-hit areas were completely destroyed or rendered uninhabitable. About 22% of the offices in Kobe's central business district were rendered unusable, and over half of the houses in that area were deemed unfit for occupancy. Although some were destroyed and others suffered severe damage, high-rise buildings that were built in compliance with the 1981 building code suffered to a lesser extent. Those that were not constructed to these standards suffered serious structural damage, such as traditional houses which had heavy tiled roofs that could weigh as much as two tons, intended to resist the frequent typhoons plaguing Kobe, but were only supported by a light wooden frame. When these wood supports gave way, the roof would crush the unreinforced walls and floors in a pancake collapse. Newer homes have reinforced walls and lighter roofs to avoid this, but are thus more susceptible to typhoons.

The damage to highways and subways was the most graphic image of the earthquake, and images of the collapsed elevated Kobe Route of the Hanshin Expressway appeared on front pages of newspapers worldwide. Most people in Japan believed those structures to be relatively safe from earthquake damage because of the steel-reinforced concrete design. Although the initial belief was that construction had been negligent, it was later shown that most of the collapsed structures were constructed properly according to the building codes in force in the 1960s. The steel-reinforcement specifications in the 1960s regulations had already been discovered to be inadequate and revised several times, the latest revision being in 1981, which proved effective but only applied to new structures.

Ten spans of the Kobe Route elevated expressway were knocked over in three locations across Kobe and Nishinomiya, blocking a link that carried 40% of Osaka-Kobe road traffic. Half of the elevated expressway's piers sustained some damage. The entire route was not reopened until September 30, 1996. Three bridges on the less heavily used Route 2 were damaged, but the highway was reopened well ahead of Route 3 and served as one of the main intercity road links for a time. The Meishin Expressway was only lightly damaged, but was closed during the day until February 17, 1995, so that emergency vehicles could easily access the hardest-hit areas to the west. It was not until July 29 that all four lanes were opened to traffic along one section. Many surface highways were clogged for some time due to the collapse of higher-capacity elevated highways.

Most railways in the region were damaged. In the aftermath of the earthquake, only 30% of the Osaka-Kobe railway tracks were operational. Daikai Station on the Kobe Rapid Railway line collapsed, bringing down part of National Route 28 above it. Wooden supports collapsed inside supposedly solid concrete pilings under the tracks of the Sanyo Shinkansen high-speed rail line, causing the entire line to shut down. 58 train cars were at Ishiyagawa Depot of the Hanshin Electric Railway when it collapsed, which rendered 24 of them damaged beyond repair. The railways rebounded quickly after the quake, reaching 80% operability in one month. The Kobe Municipal Subway resumed operation the day after the earthquake with limited service between Seishin-Chuo and Itayado stations (along with the Hokushin Kyuko Electric Railway between Tanigami and Shin-Kobe). Service resumed across the entire line on February 16, 1995, with full service resuming a month later after repairs were completed. Trains continued to operate with speed restrictions until July 21, 1995.

Artificial islands, such as the modern Rokkō Island and especially Port Island in Kobe, suffered severe subsidence due to liquefaction. Water breaking through the surface and flooding those islands was initially believed to have seeped in from the sea, but in fact had been forced out of the soil used to build the islands. The newly completed artificial island supporting Kansai International Airport was not significantly affected, due it being further from the epicenter, and because it was built to the latest standards. The Akashi Kaikyō Bridge, under construction near the earthquake's epicenter, was undamaged but was reportedly lengthened by a full meter due to horizontal displacement along the activated tectonic fault.

Nomenclature

Outside Japan the earthquake and disaster are commonly referred to as the Kobe earthquake; in Japan, the earthquake and the disaster caused by it is called The Great Hanshin-Awaji Earthquake Disaster (阪神・淡路大震災, Hanshin-Awaji Daishinsai), often shortened to The Great Hanshin Earthquake Disaster (阪神大震災, Hanshin Daishinsai) (Hanshin (阪神) refers to the area encompassing Osaka and Kobe). In the scientific literature the earthquake itself is called the 1995 Southern Hyōgo Prefecture Earthquake (平成7年(1995年)兵庫県南部地震, Heisei 7 nen (1995 nen) Hyōgo-ken Nanbu Jishin), the name given to it by the Japan Meteorological Agency the week after the main shock.