Comparing Earthquakes Aids Scientists

The earthquake that occurred this week just east of the North African city of Algiers had the exact same magnitude as the 1994 Northridge quake in Los Angeles. It erupted on the same kind of buried thrust fault and, like Northridge, was centered on the edge of a major city.

But the death toll of the 6.7 Algerian quake was nearly 30 times that of the 6.7 Northridge quake, demonstrating once again that building codes in California contribute in a major way toward safer buildings, much less prone to collapse than in many other countries, experts said.

Authorities in Algiers said Friday that the death toll has reached 1,600, with about 7,000 injured. In Northridge, deaths numbered 57, with quite a few at one collapsed apartment building, and there were about 4,500 injuries.

In another potential comparison with Southern California, the Algerian quake was apparently centered just off the coast and, by displacing seawater suddenly, generated a small tsunami that swept across the Mediterranean.

USC researchers warned earlier this month that a quake originating in a thrust fault under the Catalina Channel could likewise generate a tsunami.

Such comparisons are frequently made by earthquake scientists, who seek to learn from one earthquake to prepare for others.

In recent years, the 1995 earthquake in Kobe, Japan, and the 1999 quake at Izmit, Turkey, were compared to situations that might arise in California.

Sometimes, scientists use the example of one quake to lobby for action at another potential earthquake site.

By coincidence, the day after Wednesday’s Algerian quake, California earthquake experts gathered in Berkeley to discuss strong-motion recording instruments that are used to measure shaking intensities.

They immediately urged that, as a step to understand the variability of shaking as a way of further improving building codes, the state triple its number of 1,000 such recording instruments. The cost, over a period of years, said Tony Shakal, director of the Strong Motion Instrumentation Program for the California Geological Survey, a state agency, would run about $15 million.

Meanwhile, Paul Somerville of the Pasadena-based URS Corp. noted that California has many more of the buried thrust faults that ruptured in the Northridge quake and near Algiers.

These are also commonly called blind faults, because they don’t intersect the surface.

“I’ve been doing some research indicating that when a quake is on a deeply buried blind thrust fault, the motions are stronger than for the same magnitude quake on a surface fault like the San Andreas or the Newport-Inglewood,” Somerville said.

A similar strong quake could occur on the Puente Hills thrust fault underlying parts of downtown Los Angeles, he added.

Also speaking out in the wake of Wednesday’s quake was Brian Tucker, president of a Palo Alto firm, GeoHazards International, that devotes itself to helping Third World countries develop earthquake-resistant buildings at a lower cost than California building codes might require. Japanese and U.S. interests have helped fund this organization’s work.

Tucker said GeoHazards was founded 12 years ago “after it became clear that the average death toll of fatal earthquakes in California and Japan was going down, while in the Third World it was going up.”

Records showed, he said, that between 1900 and 1950, in earthquakes of similar size that caused at least 100 casualties, developed and undeveloped countries had about the same number of deaths. But between 1950 and 2000, the fatalities in the developed countries fell “by an order of magnitude, while in the Third World they were steadily going up.”

Even when codes are adopted that are strong, experience has shown that in such countries as Turkey, which has sustained a series of devastating quakes along the North Anatolian fault, they are poorly enforced. Also, Tucker said, materials routinely used here to strengthen buildings, such as plywood, are often unavailable in the Third World.

GeoHazards has recently been involved in a project in 20 cities in India. They are demonstrating available earthquake-resistant building techniques, often in schools, in hopes that others observing what they are doing will pick up on their ideas.