Seismic Forecast: Shaky Future or a False Alarm? : Big policy questions remain on first anniversary of Northridge quake

Of all the post-mortems on this first anniversary of the deadly Northridge earthquake, none is more chilling than a new theory from seismologists: The Los Angeles Basin is overdue for temblors that could unleash 15 times the energy of the 1994 cataclysm and topple tall buildings despite the strengthening of construction codes in recent years.

Given the havoc caused by the “moderate” Northridge quake--and the news from Kobe that a quake had knocked down hundreds of buildings and caused heavy casualties in the Japanese city--it is hard to imagine what an even larger event could do to the 15 million residents of Southern California. If the scientists are right--a very big if--there’s the possibility of a calamity that might kill and injure tens of thousands and wreak urban damage so great it would decimate the insurance industry and overwhelm the national capacity to respond to a disaster.

But no panicky reaction is warranted. The scientific findings are very inconclusive and do not represent a consensus of experts. Moreover, there is much we can do--both individually and collectively as a community--to mitigate damage from temblors.

The new findings--by teams at Caltech, USC, the U.S. Geological Survey and other institutions--were published Friday in the prestigious journal Science. In essence, the scientists argue from analyses of six major so-called blind thrust faults lacing the Los Angeles area that the region should have had at least 17 Northridge-magnitude quakes over the last 200 years to relieve geological stresses. But there have been only two, the 1971 Sylmar disaster and Northridge. Therefore, it is theorized, the region is long overdue for a truly “Big One”--magnitude 7.2 to 7.6--to dissipate this pent-up energy.

The scientists also ran a computer simulation of how new buildings would fare in a big quake. Skyscrapers in quake-prone areas today are built with flexible steel frames, and shorter buildings are erected on rubber pads meant to isolate the base from vibrations. The simulations found that pulses from a 7.0 quake could topple a 20-story building and cripple shorter ones. Cracks discovered in many steel-frame buildings after Northridge compound the worry raised by this finding.

But other scientists are skeptical: If the region is due for a Big One every 200 years, why does the known geological record not show anything spectacular for the last 3,000 years? Why would the last 200 years be anomalous? Are the faults not as contiguous as the researchers believe and thus not as potentially powerful? Has the basin been slowly relieving stress by seismic “creep,” meaning gradual, non-destructive adjustments in the faults? Stay tuned for the next pronouncement.

That said, the new report should still stir action. By most accounts, local, state and federal responses to Northridge have been excellent. And almost every Southland household today is better equipped with food, water, batteries and other essentials than before. Owners of many older homes have gone to considerable expense to bolt them down.

But the larger questions are more difficult: How much can the private and public sectors afford to invest in preparing for an unknown threat? What is the potential benefit of such an investment versus the costs? If indeed we are faced with the Big One, is it humanly possible to truly protect buildings and freeways against it?

Such questions have obviously divided members of the state Seismic Safety Commission, delaying its Northridge report to the governor. Some members want to press for a statewide upgrading of the Uniform Building Code, but others are dubious about the benefits, given the financial and political costs. Lawmakers have yet to give full consideration to imposing “seismic zoning” to deter unsuitable construction in unstable areas. The vulnerable insurance industry has been slow to address questions of how to take advantage of international advances in seismic safety--advances that surely will be assessed anew in the aftermath of the latest quake in Japan, a country that has been in the forefront of seismic preparedness.

There are admittedly no easy answers to these questions in a land that can be as terrible as it is beautiful. But they cannot be avoided.