Coastal Industrial Complexes: Risks and Anti-seismic Measures
- Blind Spots in Disaster Prevention for Earthquakes with a Tokyo Metropolitan Epicenter

Masanori Hamada
Professor,Faculty of Science and Engineering, Waseda University

Industrial complexes built on reclaimed lands

In the Great East Japan Earthquake on March 11, massive fires broke out at industrial complexes in Tokyo Bay and Sendai Port. At this writing, the causes of these fires remain unknown, however they are thought to be affected by the tsunami in Sendai Port, and liquefaction and other factors in Tokyo Bay, in addition to the quake which lasted for as long as a few minutes. In Sendai Port, heavy oil storage tanks were damaged and set ablaze, and the spilled oil traveled upstream in the river, surging into the residential areas because of the tsunami.

Meanwhile, extensive liquefaction phenomena occurred in the reclaimed lands in Tokyo Bay, causing a large number of houses and buildings to sink and tilt, and causing lifeline facilities to be damaged as well, including uplifted manholes and damaged buried pipes. This resulted in prolonged loss of city functions after the earthquake. One of the causes of the severe liquefaction phenomena could be the long duration of the earthquake.

A vast expanse of land has been reclaimed along the coastal areas in Japan’s large urban areas, Tokyo Bay, Ise Bay, and Osaka Bay. Amid the high-growth period of the Japanese economy, heavy industrial and petrochemical industrial complexes were built on these reclaimed lands. Even today, numerous tanks and manufacturing facilities for petroleum products and heavy or crude oil occupy the petrochemical-industrial complex sites.

Apprehensions over large tank fires and soil liquefaction

As for these complexes built on the coastal reclaimed lands, there are two apprehensions over future earthquakes. One is large tank fires arising from so-called long period ground motions, and soil liquefaction. Furthermore, it is predicted that the soil liquefaction-induced horizontal ground displacement by meters, so-called lateral ground flow, first causes tanks and pipes to be destroyed, and then it causes large amounts of dangerous materials such as heavy and crude oil as well as high-pressure gases to be discharged to marine waters.

Long-period ground motions are slow quakes with a duration ranging from about two seconds to 10 seconds, which do not affect normal low-rise buildings, but which did cause heavy or crude oil tank fires every time great earthquakes occurred in the past. The one that is still a fresh memory is the fire that broke out at the two tanks in Tomakomai triggered by the 2003 Tokachioki Earthquake. The tanks set ablaze were called floating roof tanks with a structure that looked like a drop lid on the surface of the content liquid. The fire is said to have broken out when large sloshing motions of the content liquid in the tanks were amplified by the long-period ground motions, their floating roofs rose with the liquid sloshing, and then dropped and collided with the tank side shells.

At present, over 600 floating roof tanks have been built and are in operation in the reclaimed lands along Tokyo Bay. According to the assumption that the Tokai Earthquake and the Tonankai Earthquake whose epicenters are situated from Tokaido to the area off Kii Peninsula occurred in series, long period ground motions in the Keiyo area and the Keihin area along Tokyo Bay were estimated, based on which the sloshing motions of the content liquid in the tanks were calculated. As a result, it turned out that the content liquid would leak out of 60 tanks, equivalent to approximately 10% of the total number of tanks. Most of such content liquid may leak into marine waters.

No anti-liquefaction measures for many reclaimed lands

The other apprehension about the seismic adequacy of coastal reclaimed lands is soil liquefaction, which also occurred in the Great East Japan Earthquake. Many of the reclaimed lands in Tokyo Bay have been developed since the early Showa era. Liquefaction phenomena were first recognized in the 1964 Niigata Earthquake, where structures sank and tilted, and underground structures including manholes were uplifted. Of course, previous earthquakes had frequently experienced soil liquefaction, however the mechanism of occurrence of liquefaction and the damage inflicted on structures had not been known.

In many cases, therefore, no anti-liquefaction measures had been implemented for embankments and soil in the reclaimed lands such as Tokyo Bay, Osaka Bay, and Ise Bay developed before the Niigata Earthquake. Liquefaction may destroy oil dikes and embankments, and the likelihood cannot be dismissed that the content liquid leaking from the tanks may flow into marine waters, causing a marine fire in the worst-case scenario.

Power reaching a crisis situation in Tokyo metropolitan area

The Japanese government established a core disaster-prevention base in the Ohgishima district off the coast of Kawasaki City. This is designed to be used for emergency response and recovery and restoration activities by bringing in relief goods and personnel from other prefectures and from abroad to this base by marine transportation, in case a major disaster takes place in the metropolitan area resulting from a an earthquake with its epicenter in the Tokyo metropolitan or southern Kanto areas. In the event that quantities of heavy or crude oil flow into marine waters, however, and then spread across Tokyo Bay by wind or tidal current, it is predicted that the sealift capability in Tokyo Bay substantially declines in the long term, and furthermore in some cases, the marine transportation in Tokyo Bay may be brought to a complete halt. This means that the core disaster prevention base would end up being virtually useless in such cases.

In addition, 12 LNG thermal power plants are in operation in the coastal areas along Tokyo Bay at present. In response to the nuclear power plant accident caused by the Great East Japan Earthquake, these thermal power plants assume a key role in power supply. However, the possible blockade of Tokyo Bay results in the stoppage of LNG supply to the power plants. This paralyzes the thermal energy supply following the nuclear energy supply, and the energy supply in the Tokyo metropolitan area is indeed expected to fall into a crisis situation.

As described above, the review on safety at the time of an earthquake has hardly been conducted for reclaimed coastal areas in large urban areas, especially marine waters. Although some local municipalities have been addressing issues relating to the possible liquefaction in reclaimed lands and the review of coastal safety, both the government and local municipalities have left the issue of the safety of marine waters which spread out in front of the reclaimed lands almost untouched. It can be regarded as a veritable blind spot—an area neglected among disaster prevention measures.