Science: Four-Year Quake

A noticeable tremor has shaken the North Atlantic seaboard about every four years since 1925. Last week the quadrennial earthquake arrived close to schedule (last one was in December 1940). The New York Daily News cried: QUAKE EAST’S WORST IN 58 YEARS. In Philadelphia, seismologists reported it as the sharpest shock in the city’s records. Tremors were felt from Canada to Virginia and as far west as Wisconsin. But, except in Cornwall. Ont., which reported $1,000,000 damage, no one was hurt.

Harvard Seismologist Lewis Don Leet thinks that Easterners are much too complacent about earthquakes. Last week, renewing his warning that quakes are likely to be more & more frequent on the eastern seaboard, he declared: “If the epicenter had been near a city the size of Boston, it would have constituted a real hazard.” The theory that the Atlantic Coast is safe from really destructive earthquakes is, after all, only a theory.

Slides and Squeezes. No one knows just what causes an earthquake. Geologists are moderately sure that it is touched off by a subterranean rock slide along a “fault” (fracture) in the earth’s crust, which makes the earth surface quiver like jelly. Last week’s temblor was attributed to the well-known Laurentian fault in the St. Lawrence valley. Because severe earthquakes occur most often in the mountainous, volcanic areas around the Pacific and the Mediterranean, geologists suppose that their prime cause is the dislocation of sections of the earth’s crust by mountain-building forces—possibly the shrinking of the earth’s skin, the earth’s wobbling on its axis, subterranean radioactivity or heat currents. A quake comes when the rock layers at a major fault suddenly slip under these accumulated stresses. The comparatively mild tremors in the solid old geological formations of the eastern U.S. and Canada are put down to minor faults caused by the earth’s slow recovery from the great squeeze of the Glacial Age. Since the glaciers melted, the earth, like a squeezed sponge, has been swelling again.

These speculations, however, leave many earthquake facts unexplained. Seismologists record an average of 150 severe earthquakes each year, most of them under the sea. One of the biggest on record took place in 1929 off the coast of Newfoundland, only 800 miles from New York City; it raised waves 50 feet high and snapped twelve transatlantic cables.

Engineers think that modern cities could weather even a severe earthquake. Because of its flexible steel frame, probably the safest refuge would be a skyscraper.