Volcano Watch — Earthquakes: Lessons for Hawaii from Kobe

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The magnitude 7.2 earthquake in Kobe, Japan has resulted in extensive damage and a shocking number of fatalities and injuries. Japan has not experienced such a damaging earthquake since 1923, when an estimated magnitude-8.3 earthquake killed about 143,000 people in the Tokyo area.

The magnitude 7.2 earthquake in Kobe, Japan has resulted in extensive damage and a shocking number of fatalities and injuries. Japan has not experienced such a damaging earthquake since 1923, when an estimated magnitude-8.3 earthquake killed about 143,000 people in the Tokyo area. However, this was the eighth earthquake in Japan in this century that caused more than 1,000 deaths. These included one with magnitude 7.9 in 1927, an 8.9 in 1933, a 7.4 in 1943, an 8.3 in 1944, an 8.4 in 1946, and a 7.3 in 1948.

The level of damage to the infrastructure, particularly to underground water and gas lines, and to transportation routes such as roadways, railways, and port facilities, enhanced the damage and thwarted relief efforts. Similar problems of broken gas and water mains occurred in both the Loma Prieta and Northridge earthquakes in California. The broken gas mains cause post-earthquake fires, and the broken water mains disrupt water supplies so that there is no water to fight the fires. Uncontrolled fires caused most of the damage in the infamous 1906 San Francisco earthquake, as well. Disruption of transportation infrastructure, mainly freeway collapses, also occurred in both California earthquakes. Neither area in California has fully recovered, despite the elapsed year since the Northridge earthquake and the more than four years since the Loma Prieta earthquake.

Perhaps most surprising about the Kobe earthquake has been the sheer number (greater than 20,000) of heavily damaged or destroyed buildings, particularly one- and two-story wood frame structures. The damage has been concentrated in older buildings, because newer buildings have been built to improved standards for earthquake resistance. Each major destructive earthquake teaches new lessons in how to build structures that will withstand earthquakes. Following such earthquakes, engineers rush to examine the damage and to document designs that failed. Building codes can then be modified so that still-to-be constructed buildings will not include designs that are inadequate for earthquake resistance. However, at any time and in any region, the vast majority of existing buildings were constructed using older, outdated building codes. In many cases, retrofitting structures with particularly vulnerable designs should be done to avert future disaster. For these reasons, it is important that the most recent building code be adopted and enforced. At least the newest buildings will be earthquake resistant.

Extensive damage from earthquakes occurs for particular reasons: it may be that the earthquake was especially large, that it occurred close to densely populated areas, or that the area affected has unconsolidated soils or bay fill that amplify the ground shaking. The Kobe earthquake was not unusually large (there are about 18 magnitude-7 or greater earthquakes worldwide each year), but it did occur close to the center of the city, which was built on unconsolidated sediment that apparently amplified the shaking and also liquified in some areas.

The Island of Hawaii also has a high earthquake hazard, but because of the relatively small population and lower population density, it does not have as high a risk as most parts of Japan (or California). Many of the effects of large earthquakes in these more densely populated regions will not be the main post-earthquake problems here. For example, we have no elevated freeways or railways to be damaged, although damage to bridges could hamper transportation. The lack of alternate transportation routes in many areas, such as Puna and the Hamakua coast, could severely limit movement on the island following a large earthquake.

Similarly, underground gas mains that could break during a large earthquake occur only in Hilo and in downtown Kailua. You should know how to turn off the gas at the main valve outside your home in case of leaking gas following an earthquake. In outlying areas, the widespread use of propane gas stored in poorly secured tanks consitutes a major hazard on the island. Securing such tanks is the single most important thing you can do to reduce your earthquake risk. Underground water mains are always vulnerable to rupture during strong ground shaking. However, those of us with catchment systems are also vulnerable, since these tanks commonly collapse during earthquakes. The best remedy, regardless of your water source, is to maintain bottles of drinking water in various locations in your home.

Here on Hawaii, as in Kobe, we would have problems with telephone and electrical service. However, because of the long distances that electric and telephone lines traverse here, the amount of damage and the down-time might be even longer than in more densely populated areas. In part, this reflects a lack of alternate routes on the island, compared with the dense grids that exist in densely populated regions.

Wood-framed structures generally perform well during ground shaking unless they are not tied down to a solid foundation. Many homes on Hawaii are constructed with post-and-pier foundations. When earthquakes occur, such homes tend to walk off the piers, causing severe structural damage. Homes where the posts are one-story tall are particularly vulnerable. Such damage was observed during the earthquakes in Honomu in 1973, in Kalapana in 1975, near Volcano in 1983, and again in Kalapana in 1989. There are ways to retrofit such post-and-pier foundations to increase the earthquake resistance of your home. The newly adopted 1991 Unified Building Code requires that new homes are built on, and secured to, a solid foundation or a slab. Such construction will reduce the damage from future earthquakes, although, as observed in Kobe, older homes built under less stringent building codes will still be vulnerable during large earthquakes.