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Rest of U.S. Is Not Immune to Temblors, Experts Warn

October 11, 1987|From the Associated Press

People outside quake-prone California and Alaska have no reason to feel smug, scientists warn: Killer earthquakes once rocked the Midwest, East Coast and possibly the Pacific Northwest, and likely will do so again.

"The potential is there at any given time to produce a catastrophe almost anywhere in the country," said David Russ, an assistant chief geologist for the U.S. Geological Survey. "The only difference is the events are better understood in California because they are more frequent there."

"Earthquakes are a national problem," he said during a telephone interview from USGS headquarters in Reston, Va. "Earthquakes have occurred in a great many of our states significantly large enough to produce some damage."

Giant and large temblors occur far less often elsewhere in the nation than in California and Alaska, where the sparsely populated Aleutian Islands are often rocked by quakes measuring 7 on the Richter scale.

Construction Not Quake-Resistant

But Central and Eastern states "don't have earthquake-resistant construction practices, so a lot of those places could be in for a worse disaster when they do have an earthquake," said seismologist Kate Hutton of the California Institute of Technology in Pasadena.

Russ, USGS seismologist Tom Heaton in Pasadena and seismologist Lynn Sykes of Columbia University's Lamont-Doherty Geological Observatory in Palisades, N.Y., said four regions outside California and Alaska are most likely to be shaken by destructive temblors sooner or later:

- The Central States, where four quakes with magnitudes that, it is estimated, would have registered up to 8.6 on the Richter scale (which was not developed until 1935) ruptured the New Madrid, Mo., seismic zone during the winter of 1811-12. The quakes were the largest in recorded history in the contiguous 48 states. They killed several dozen people, toppled cabins, snapped trees, temporarily reversed the flow of the Mississippi River, caused some damage in Chicago and Cincinnati, and cracked pavement and rang church bells as far away as Washington, D.C., New York and Boston.

- The East Coast, which was rocked by a quake estimated as approaching magnitude 7 near Charleston, S.C., on Aug. 31, 1886, collapsing buildings in South Carolina and killing about 60 people.

- The Pacific Northwest, including Oregon, Washington state and Vancouver Island, British Columbia. Heaton said growing evidence suggests the region was ravaged by prehistoric 9-magnitude monster quakes every 500 to 1,000 years, inundating coastal areas with tsunamis, or quake-caused sea waves. Sykes said evidence for such quakes is inconclusive, but jolts up to 6.5 have occurred.

- The Nevada-Utah-Montana seismic zone, which has been shaken by large quakes, including the 1959 Hebgen Lake, Mont., shock that Sykes said killed about two dozen people in landslides.

In addition, Sykes said, "We certainly have to be prepared to expect magnitude-6 earthquakes in various parts of the Northeast. The places that are more prone historically would be along the East Coast, including Boston, New York and Philadelphia, and in the Northeast, from northern New York state into Canada."

Because the ground east of the Rockies is much older, cooler and more brittle than in the West, quakes there are felt over areas 10 times larger than in the West, Sykes said.

Risk Called Comparable

"So the cumulative risk in California versus east of the Rocky Mountains is probably about comparable," he said.

"There have been very large earthquakes in other parts of the country, some of which, if they occurred today, would be very destructive, perhaps even more destructive than California earthquakes," Heaton said.

A study written nearly three years ago by the Memphis, Tenn., engineering firm of Allen & Hoshall said a repeat of a New Madrid quake today could cause 4,500 deaths and $51 billion in damage in Little Rock, Ark.; Memphis; Carbondale, Ill.; Evansville, Ind.; Paducah, Ky.; and Poplar Bluff, Mo.

Russ said such jolts could whip skyscrapers in Chicago and Detroit, causing non-structural damage.

Subduction Quakes

The monster jolts that may have rocked the Northwest were "subduction" quakes, caused as the offshore Juan de Fuca plate--one of the giant pieces of ground that make up Earth's crust--was thrust beneath the North American plate.

Subduction quakes shake broader areas and can be much more intense than the type of quakes that occur when the Pacific plate slips horizontally past the North American plate along California's San Andreas Fault.

Similar subduction quakes include the 8.1-magnitude, Sept. 19, 1985, Mexico City quake, which killed at least 6,000 and possibly 30,000 people, and the March 27, 1964, Anchorage, Alaska, quake, which had a magnitude estimated between 8.5 and 9.2 and produced tsunamis that ravaged Valdez and Seward, Alaska, and Crescent City, Calif., killing about 120 people.

"Other parts of the country are ill-prepared to deal with earthquakes that probably will hit them sometime in the next couple hundred years," Heaton said. "I'd tell them to pay attention to the things that happen in California earthquakes, because when they get theirs, they'll have to deal with similar problems."

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