Apple SOS: New York and the 'big one'?

Apple SOS: New York and the "big one'?

Worry over when the big earthquake will strike would appear to be part of the California lifestyle--not something found on a New Yorker's list of anxieties. But if measurements by a team of California scientists are correct, the New York City area may someday be the center of a destructive earthquake.

Localized strain in rocks near the earth's surface apparently is accumulating at rates comparable to those observed near the notoriously active San Andreas fault in California, according to a report in the Oct. 24 NATURE. "Such rates could probably not be sustained in the lower crust for more than several hundred years without a major earthquake occurring,' write coauthors Mark Zoback of Stanford University, William Prescott of the U.S. Geological Survey in Menlo Park, Calif., and Scot Krueger of the University of California at Berkeley. But how movement on the earth's surface relates to deformation deeper in the crust, where earthquakes originate, is uncertain.

Their conclusions are based on analyses of National Geodetic Survey (NGS) records from 1872 to 1973 for northeastern New Jersey and southeastern New York, where they found slight movement of surface survey markers in western Long Island and along a 60-kilometer stretch of the Hudson River's eastern shore. Amid the continuing controversy that clouds earthquake prediction, the study raises some new points for geophsicists to ponder.

Geological differences between New York and California make interpretation of the data all the more interesting. Subsurface rocks in California are weaker and less dense than their eastern counterparts, which contain no known large, active faults. But the principal dissimilarity may be that California sits on the unstable edge of a massive plate of rock, while the "edge' nearest New York lies in the middle of the Atlantic Ocean. "More important than what we found in New York was the underlying concept of intraplate seismicity,' Zoback told SCIENCE NEWS. "We're looking at a phenomenon that's never been observed before.'

The findings don't guarantee a large quake will occur, but Zoback says the region's series of smaller quakes is consistent with the data. The Oct. 19 shaker centered in Ardsley--the area's 16th in the last 250 years estimated at magnitude 3.5 or greater--occurred next to the region assayed by Zoback's group.

Also located nearby is the Lamont-Doherty Geological Observatory (LDGO) in Palisades, where some are taking a "wait and see' approach to the new data. One LDGO seismologist, who asked not to be identified, called the strain rates "just absolutely astonishing' because of their intraplate location. But unpublished data from an LDGO bore hole experiment and a similar NGS analysis of marker movement appear to corroborate the high strain rates. As LDGO geophysicist Dan Moos told SCIENCE NEWS: "The big unanswered question . . . is how much stress is necessary before an earth quake will happen.' So no one can say whether the unsettling rates in New York will cause a quake as large as that said to threaten California.