Kobe earthquake

Earthquake

Also known as: The Great Hanshin-Awaji Earthquake, the South Hyogo Prefecture earthquake

Date: January 17, 1995

Place: Kobe, Japan

Magnitude: 7.2

Result: 5,502 dead, 37,000 injured, 200,000 buildings destroyed or damaged, more than $50 billion in damage (the most financially costly natural disaster to that time)

The city of Kobe (pronounced koh-beh) lies on the southern coast of Japan’s main island of Honshū. Situated on the Inland Sea between the islands of Honshū and Shikoku, it is Japan’s second largest seaport and an important center for shipbuilding, steel-making, and other commerce and industry. Its population of 1.4 million is densely concentrated along the narrow coastal plain that fronts inland mountains.

Without warning, just before dawn on the wintry morning of January 17, 1995, the Kobe area was struck by an earthquake that would be the most devastating seismic event in earthquake-prone Japan since the Tokyo quake of 1923, and the most expensive natural disaster to that time. The epicenter was 20 miles (32 kilometers) southwest of downtown Kobe, at 34.6 degrees north latitude and longitude 135 degrees east. This was about 19 miles (30 kilometers) south of the coastline, near the tip of Awaji Island. Slippage occurred on the Nojima fault, including surface rupture along at least 6 miles (9 kilometers) with displacement (slip) up to 5 feet (1.5 meters), and perhaps 6.5 feet (2 meters) depth. The total length of the ruptured fault at depth was 19 to 31 miles (30 to 50 kilometers). The movement was lateral (strike-slip), with the fault oriented to the northeast toward the northern portion of the city of Kobe. The focus (zone of initial slip) was at a depth of 13 miles (21 kilometers) below the tip of Awaji Island.

This event has been called the Great Hanshin-Awaji Earthquake or the South Hyogo Prefecture earthquake, after the local province, but internationally it is more commonly known as the Kobe earthquake for that nearby city. While it was not a truly great earthquake in magnitude and energy release, it had devastating consequences for people and urban structures because of its proximity to Kobe and the densely populated corridor along the coast, because of the orientation of the rupture directly toward the city, and because of the shallowness of the rupture.

The magnitude of the main shock was 7.2 on the Richter scale, and 6.9 on the moment-magnitude scale. It occurred at 5:46 a.m. local time on January 17, which was 8:46 p.m. January 16, Universal time (Greenwich Mean Time). Aftershocks continued for many months after the initial major shock. In the seven days after, there were nineteen aftershocks having magnitudes of 4 to 5. People reported that the approaching seismic waves created a rumble, then a roar, followed by strong vibrations both vertically and horizontally. The wrenching vibrations lasted about twenty seconds.

Aftereffects. The casualties and destruction were staggering. At least 5,502 people were killed, mostly from immediate crushing or entrapment in the rubble. This figure included 28 who were killed in a landslide at Nishinomiya, a town just east of Kobe. Early reports revealed 27,000 injured, but this was later raised to 37,000. As many as 310,000 people had to be evacuated to temporary shelters, including school gymnasiums and city offices, and over 70,000 were still in those shelters two months later. Initially, many residents had to camp out in the freezing January weather, having lost their homes or being afraid of more damage and collapse from the continuing aftershocks. According to the international edition of Newsweek for January 30, 1995,

Approximately 200,000 buildings were destroyed or damaged. More than 50,000 were reduced to rubble or complete collapse, thousands of others were so damaged that they had to be torn down, and others were consumed in the subsequent fires. While some modern structures, especially those built to an earthquake-resistant code (with reinforcing and bracing) instituted in 1981, were relatively unscathed, many suffered damage. Some collapsed, tilted, or sank because of unstable or settling soil and sediment.

Superficial ground accelerations in Kobe and adjacent Nishinomiya were measured at up to 50 to 80 percent of the acceleration of gravity—too high for most unreinforced structures to withstand. When materials (soft soil, alluvial deposits, landfill) are unconsolidated, and especially when they are water-saturated as after rains and in coastal regions, they lose strength and absorb energy when vibrated by seismic waves. Ground motions are amplified, and damage is intensified. This behavior, termed liquefaction, causes much worse damage than that received by structures on firm bedrock. Some of the worst structural damage was thus along the Kobe waterfront, with its water-saturated landfill in place for port development and creation of habitable land for the expanding population.

Portions of the elevated Hanshin four-lane expressway, Japan’s primary east-west traffic artery through coastal Kobe, collapsed. A section 656 yards (600 meters) long toppled over sideways to rest at a 45-degree angle. There was much ground failure, cracking, and sinking along the waterfront. The elevated rail line of the high-speed Shinkansen (“bullet”) train, constructed to be almost indestructible, was snapped in eight places. Fortunately, the first train of the day had not yet left for Kobe.

Particularly vulnerable to the horizontal shaking of earthquake waves were the older two-story houses built of wood frames with heavy tile roofs. They collapsed, trapping their occupants, and were then burned in fires ignited by ruptured gas lines. There were over 300 fires in the area, and a dozen of them raged for twenty-four to forty-eight hours. Fire fighting was impossible, because major utilities—water mains, as well as electricity, gas, and telephone lines—were severed and disabled. Further, the roadways were congested with fallen buildings, rubble, and people fleeing, checking on relatives, or engaged in rescue efforts. Roads, bridges, and rail lines (for the public transportation electric trains) were cut. With the loss of utilities, there was no heat for the cold January weather and no water for drinking, plumbing, or bathing.

Factories and shops that did survive the earthquake had to shut down operations because of lack of power and other utilities, toppled equipment, and lack of employees. Despite the destruction and abandonment of homes, stores, and shops, there was virtually no looting or civil disturbance. The Japanese virtues of order and discipline, stoicism, and civility were evident and focused the citizenry on applying their perseverance and hard work to the tasks of survival and reconstructing their lives.

Damage and casualties occurred along the coast through Nishinomiya and as far as Osaka, Japan’s second-largest city, which is 18 miles (30 kilometers) from Kobe. The latter had cracked walls, broken windows, and 11 earthquake-related deaths.

Japan is a nation with high cost of living and an elaborate urban infrastructure. Rebuilding costs, public and private, have been variously estimated from U.S. $40 to 100 billion—exceeding those of any other natural disaster to that time. This figure does not include indirect losses such as lost economic productivity and business activity. Little of the residential losses was covered by insurance—only 9 percent of Japan’s population has home earthquake insurance, and only 3 percent in Kobe, which was thought to be in a region of low seismic risk.

Rescue and Relief. The rescue efforts and distribution of emergency relief materials—food, water, fuel, and blankets—were hampered by an initially slow response by local government authorities and uncharacteristic disorganization. Assistance was also slowed by the congested urban destruction and impassable roadways. Roads that could have been cleared for emergency vehicles—fire, police, and search and rescue—were not cordoned off and thus became clogged with residents with their vehicles and possessions. The officials also delayed in calling in the national armed forces for assistance.

The lack of civic preparedness for such an earthquake disaster was surprising, considering the generally high awareness in Japan of the prospect of such an event. Many people have an earthquake-emergency kit of supplies in their homes. Every September 1, Disaster Prevention Day, on the anniversary of the Great Kwanto Earthquake that hit Tokyo and Yokohama in 1923, there are nationwide community drills on disaster response, evacuation, mock rescues, and protective measures. Ironically, Kobe rose to become a busy port and international trading city in 1923, when foreign merchants left the devastated port city of Yokohama after the earthquake there. In fact, some Japanese survivors of the 1923 earthquake had come to Kobe to settle and were still alive for the 1995 event—thus experiencing the two most devastating earthquakes in Japan in the twentieth century.

Reasons for the Scope of the Destruction. Kobe was not well prepared, psychologically and organizationally, for a major earthquake. First, it was some distance back from the seismically active zone of earthquakes associated with the oceanic trenches off Japan’s southern and eastern margins. It was thus believed to have less potential for suffering a major shock. Second, there was a belief that modern engineering and building design had made structures less susceptible to being damaged and disabled by an earthquake. This event, having a fairly large magnitude and being shallow and nearby, demonstrated the continuing vulnerability of an urban infrastructure.

Third, there was an expectation, or hope, that Japan’s application of technology to the problems of understanding earthquake mechanisms, monitoring for precursory indications of an impending event, and public warnings issued to the citizenry would give advance warning of a likely event. Unfortunately, the earthquake struck on a then-unsuspected fault and without any obvious premonitory indicators such as minor foreshocks. However, there were reports of odd animal behavior near Kobe in the hours and days before the earthquake. These included fish near shore, birds, and sea lions at the zoo. The composition of well water used for local sake (rice wine) production varied unusually—especially for radon, a gas whose presence in deep groundwater has been linked to pre-earthquake straining.

Ironically, on the day the earthquake struck Kobe, the fourth Japan-United States Workshop on Urban Earthquake Hazard Reduction was beginning down the road in Osaka. After the earthquake, the meeting was canceled because the participants had gone to Kobe to assess and investigate the disaster and its consequences.

Three years after the earthquake, in April, 1998, the world’s longest suspension bridge opened there. The Akashi Kaikyo bridge connects the mainland west of Kobe across the Akashi Strait to Awaji Island. Its total length is 15 miles (24 kilometers), and the center suspension span is 1.2 miles (2 kilometers) long. The bridge is designed to withstand a magnitude 8.0 earthquake. Each of the tall towers supporting the center span is equipped with 20 vibration-control pendulums to reduce bridge movement if buffeted by earthquake waves or high winds.

This was the biggest earthquake to hit a densely populated area of Japan since June, 1948, when a magnitude 7.1 quake struck Fukui, on the north coast of Honshū island, killing about 5,000. With Kobe’s death toll of 5,502, it was the deadliest seismic disaster since the September, 1923, Great Kwanto Earthquake of magnitude 8.3 that struck Tokyo and Yokohama and killed 143,000, mostly in the fires that raged after the shock.

The geological fact of life for Japan is that the beautiful island nation, the world’s second-largest economic power, is constructed on vulnerable and unstable terrain. The inexorable movement and collision of tectonic plates—the Pacific and Philippine from the east, the Eurasian from the west, and the North American from the north—mean that faults will continue to rupture and cause earthquakes into the foreseeable future.

Everything but misery was in short supply. Many people spent the nights in the open air because no one could provide them with shelter. One moment they were well-dressed, propertied, and secure; the next they were refugees shuffling through rubble-strewn streets fretted by flame, lugging possessions on their backs, surrounded by the corpses of loved ones and neighbors.

Bibliography

Proceedings of the International Symposium on Earthquake Engineering Commemorating the Tenth Anniversary of the 1995 Kobe Earthquake: January 13-16, 2005, Kobe/Awaji, Japan. Tokyo: Japan Association for Earthquake Engineering, 2005.

Reid, T. R. “Kobe Wakes to a Nightmare.” National Geographic, July, 1995, 112-136.

Schiff, Anshel J., ed. Hyogoken-Nanbu (Kobe) Earthquake of January 17, 1995: Lifeline Performance. Reston, Va.: American Society of Civil Engineers, 1999.

Shea, Gail Hynes, ed. Lessons Learned Over Time. Oakland, Calif.: Earthquake Engineering Research Institute, 2000.

Somerville, Paul. “Kobe Earthquake: An Urban Disaster.” EOS/Transactions of American Geophysical Union 76, no. 6 (February 7, 1995): 49-51.

“Twenty Seconds of Terror.” Newsweek, January 30, 1995, 19-30.