Soviet Quake Site, L.A. Basin: Geological Similarities

The devastating earthquake that hit the Soviet Union on Wednesday struck in an extremely complex geological region that in many ways resembles much of the Los Angeles Basin, according to scientists familiar with the area.

The driving force in both places is the convergence of two giant tectonic plates--the massive slabs of the Earth’s crust that support the continents and the oceans. Although the Soviet situation is vastly more complicated than Southern California’s, both systems create pockets of high seismic stress because of compression of the land, several experts said.

And in both cases, the result is the creation of hidden earthquake faults similar to those discovered in the last year in the Los Angeles Basin. Lurking several miles beneath the surface, these “thrust” faults cause earthquakes when one side of the fault is pushed over the other in a process that releases enough energy to level cities.

‘Very Complex’ Geologically

Lev Zonenshain, a Soviet geologist who specializes in the study of the forces that drive the tectonic plates, described the region of the Soviet Union where the quake occurred as “very complex” geologically. The epicenter of the quake was in the Caucasus Mountains region, along the border between Armenia and Soviet Georgia and about 25 miles from the Turkish border, in a region laced with minor faults and dormant volcanoes.

“So it is very difficult to predict what kind of earthquake could occur,” he said. Zonenshain, who is affiliated with the Institute of Oceanology in Moscow, was here to present a scientific paper at the fall session of the American Geophysical Union.

Because quakes in this area of the Soviet Union occur on faults close to the surface, they often are far more damaging than their size would suggest, said acting California State Geologist Brian Tucker, who spent two years studying the seismology of the area near where the earthquake struck.

Estimated at 6.9

U.S. scientists have estimated the Soviet quake at magnitude 6.9. Early reports from the Soviet Union indicated a magnitude of about 8, but the Soviets were using the so-called MKS scale, which measures the intensity of ground motion at the epicenter, rather than other scales, including the Richter scale, which measure the amount of energy released.

“An MKS value of 8 is perfectly consistent with a Richter magnitude of 6.9,” geologist William Leith of the U.S. Geological Survey said.

“A 6.9 earthquake that is shallow in the crust often does a lot of damage,” Tucker said. He estimated that a similar earthquake in the Los Angeles Basin would kill about 1,000 people because there are still many unreinforced masonry buildings in the area, and “those structures don’t do very well.”

Buildings Vulnerable

Roger Bilham, a seismologist with the University of Colorado who also has studied the Soviet region, said most structures in the area are poorly designed for earthquakes. And he noted: “Earthquakes don’t kill people. Buildings do.”

Several experts compared the Soviet region with Southern California, but there are significant differences.

In both places the land is compressed because “you have two big pieces of real estate that are pushing against each other,” said Mdansour Niazi, an Iranian geophysicist who now works as a consultant in Berkeley.

The primary manifestation of that process in Southern California is the San Andreas Fault, but there is no counterpart to that in that area of the Soviet Union.

“There are no defined lines of seismicity,” Niazi said. “It is very diffused.”

Thus, it is much more difficult to know exactly where earthquakes will strike there, even though the entire region is extremely active geologically along a structure called the Alpine Belt that stretches from Europe to the Far East.

That belt has been the site of many disastrous earthquakes in this century. For example, a magnitude 7.7 temblor in Tabas, Iran, in September, 1978, killed 25,000 people, while a magnitude 7.9 temblor in Erzincan, Turkey, in December, 1939, killed 30,000. Other earthquakes in this century in the belt have killed from 1,300 to 12,000 people.

Times science writer Thomas H. Maugh II in Los Angeles contributed to this article.

EARTHQUAKE TOLL MOUNTS IN SEISMICALLY ACTIVE REGION

The devastating earthquake that hit near Leninakan in Soviet Armenia Wednesday occurred in an extremely complex geological region that has been the site of several major temblors in the last 50 years. Twelve earthquakes, with 6.8 magnitude or more--far greater than any that have occurred in Southern California in recent years--have killed nearly 96,000 people. The death toll in Armenia has not been determined.

1. Gediz

March 1970

7.4 magnitude

1,086 dead

2. Erzincan

Dec. 26, 1939

7.9 magnitude

30,000 dead

3. Pasinler

Oct. 30, 1983

7.1 magnitude

1,300 dead

4. Leninakan

Dec. 7, 1988

6.9 magnitude

5. Varto

Aug. 19, 1966

6.9 magnitude

2,520 dead

6. Lice

Sept. 6, 1975

6.8 magnitude

2,312 dead

7. Van

October 1983

7.9 magnitude

4,000 dead

8 .Hamadan

Dec. 13, 1957

7.1 magnitude

2,000 dead

9. Zarand

Sept. 1, 1978

7.1 magnitude

12,230 dead

10. Northeast of Tehran

July 2, 1957

7.4 magnitude

2,500 dead

11. Khorasan province

Aug. 31, 1968

7.4 magnitude

12,000 dead

12. Tabas

Sept. 16, 1978

7.7 magnitude

25,000 dead

13. Qir

April 10, 1972

6.9 magnitude

5,057 dead

Source: Times wire services, U.S. Geological Survey, National Earthquake Center