John G. Anderson
Reno Gazette Journal
P. O. Box 22000
Reno, NV 89520
Attn: Bruce Bledsoe, Editorial Page Editor
Dear Mr. Bledsoe:
Please consider the attached article for your Op Ed column, "My Turn". The opinions expressed here are my own, and not those of any department at the University of Nevada. However, I have asked colleagues to read the letter for scientific accuracy.
Thank you.
Sincerely yours,
John G. Anderson
Professor of Geophysics
Acting Director, Seismological Laboratory
I commend your editorial ("Japanese earthquake should make us stop and think", January 24) for encouraging us to examine our expectations from earthquake resistant construction. Contrary to some initial reports, studies in Kobe, Japan, will probably confirm that not all of the damaged buildings and freeways were "state-of-the-art", and that the design of structures did make a difference. The Northridge, California, earthquake is also relevant, since the loss of life, at least, was a hundred times smaller even though the shaking was about as strong and the population about as large. Thus, your byline ("Are we wasting millions building structures that won't survive anyway?") is unjustly pessimistic. But the issue is more complicated.
The time to start to prepare for a severe earthquake is decades beforehand, when buildings are being built. It is much less expensive to build a stronger structure in the first place than to strengthen it later or to rebuild or repair it after it has been damaged.
A critical decision might take place when design standards are established. That decision is whether to design for the worst case earthquake at the site, or for a more common event that is less severe. The reason to design for the worst case event is to minimize risk. The argument in favor of the alternative is that the lower cost saves funds for other purposes. Stated simplistically, for government the decision might mean spending a little more on a bridge or a building in the first case, or a little more on its other obligations in the second. For a private company, the higher cost of greater earthquake resistance might contribute to pressures to locate elsewhere, raise prices, or cut costs. Accepting lower standards implies that the community accepts higher costs from a rare, severe event.
In the most populous parts of California, the decision on whether or not to build for the worst case is easy. The chances are high that the worst case event will happen during the life of the structure. In north-western Nevada, we think the opposite is true. The worst case earthquake for Reno, Sparks, or Carson City may occur only once every 1000-2000 years (NOTE 1). However, when it strikes, the shaking will be just as strong as it was in Kobe or Northridge. By coincidence, based on preliminary data, earthquakes on the faults that damaged Kobe and Northridge happen about as often as the worst case earthquakes in the Truckee Meadows.
Currently, for ordinary structures, Reno and Sparks accept the recommendation of the Uniform Building Code, which places us in Seismic Zone 3 (NOTE 2). California's largest cities are in Zone 4, which implies a somewhat stronger, but more expensive, design. It is significant, though, that research and ingenuity are contributing to give structures greater earthquake resistance at lower cost - a trend that is likely to accelerate. When we "stop and think" about our hazard, we should ask whether our local government should require Zone 4 seismic resistance. The State of Oregon recently made that decision (NOTE 3). The decision to exceed the Uniform Building Code recommendations may be justified by our own special circumstance - an economy that depends on a good image with potential tourists worldwide. But it would take political courage, considering that the consequences might include some slowing of the regional growth or diverting funds from other critical needs.
NOTE 1. This is the estimated repeat time for a magnitude 7 earthquake on the northern half of the Genoa fault. In no way should anyone interpret that this is the repeat time for a "damaging" earthquake. There are several other sources of potential damaging earthquakes in our area. Historical records show nearby magnitude 6 earthquakes in 1984, 1966, 1948, 1914 (2), 1887?, 1869, 1868, 1860, and 1852. There are several faults nearby that are definitely capable of large damaging events, but I think they are all a little less severe than the "worst case".
NOTE 2. Actually it is a little ambiguous. The boundary between Zone 3 and Zone 4 is very close to Reno. My impression is that most engineers in the Truckee Meadows consider that we are in Zone 3, and do not want it increased to Zone 4. John Bell told me afterwards, however, that the boundary is intended to go up the Sierra Nevada frontal fault system, and include us in Zone 4. The fact seems to remain, however, that the local government accepts Zone 3 designs.
NOTE 3. Actually, Oregon upgraded to Zone 3. The important point is that local government can make the decision to upgrade if there is the political will.