Hi All. A quote from EQF. “If we do eventually lose one of our cities to an earthquake I am expecting to almost immediately hear in the news: “It is unfortunate that this city no longer exists. But as scientists all agree (translation: ‘all of the ones that we want to listen to’), ‘Earthquakes can’t be predicted.’ So, too bad.”

While it may be true that major quakes can bring down even the best well built construction be it bridges, homes, or work places you can still build so that the over all damage is kept at a minimum. The type of construction or configuration used is almost certain to either survive a major quake, or be completely destroyed.

Foundations are often an area of weakness in older houses. Sometimes older houses do not have foundations at all, or they have weak ones. Most houses have perimeter wall foundations, which are continuous at the ground around the edge of the house. Many newer houses have concrete slab foundations that perform well in earthquakes. The most common problem in wood frame houses is in the area between the floor of the house and the top of the foundation, either this part of the structure is poorly braced or not well-bolted to the foundation. Over 23,000 homes were damaged in the Loma Prieta earthquake of October, 1989, and most of the damage was due either to lack of anchor bolting to foundations or in adequately braced cripple walls.

Even in recently constructed houses, there are features that have proven to be vulnerable to earthquake damage; most of them relate to the building configuration. Particular configurations have been associated with damage in past earthquakes:

1) house over garage

2) many large windows or doors (particularly at building corners)

3) large overhangs

4) split levels and complex geometry

5) stilts supporting the structure (as on a hillside site)

A recent survey of buildings in San Francisco that with stood the 1906 quake showed that the way the building was placed in regards to the shock wave from the quake determined whether the building stayed up or came down. When the wave from the quake struck the building head on it withstood the quake quite well, but those that were struck from the side were all but destroyed. The same thing was seen in the mobile home park I live in, but in this case the opposite was true. During the Loma Prieta quake most of the homes that came off the blocks were aligned on a north/south axis. Only a small number of those with an east/west alignment came off the blocks. My home moved a half-inch on the blocks. The north/south alignment was more venerable because of the orientation of the blocks. They had an east/west alignment and were like dominos.

Most of the homes that were destroyed in the Kobe, Japan quake were two story homes with heavy tiled roofs and lightly supported walls. The bottom part of the house was literally jerked out from the upper part of the house.

It is true that large quakes can and do destroy buildings and what have you, but the damage can be minimized if we build for the strongest quake that could occur in a given area. A megaquake is survivable as the 1964 Alaskan quake showed and I suspect that none of the buildings there were built with just such a quake in mind, but some were built to withstand a large quake.

Maybe the Japanese are right. Earthquake prediction may not be the way to go. You can get the people out of harms way, but you can’t move the buildings out of harms way. The Japanese are learning that it costs more to rebuilt then to built it correctly in the first place. Take Care…Don in creepy town