And while sections of Alaska have been ominously quiet, California's San Anreas fault has been going though a "noisy" spell that scientists find interesting and a bit worrisome.
"Taking the whole of southern California, the number of moderate earthquakes just about doubled beginning in mid-1978 and lasting to the start of 1980," said Don Anderson of Caltech.
This increase roughly coincides with a temporary change in stresses along the San Andreas fault, changes some scientists thought might encourage earthquakes.
The fault, which runs nearly two-thirds the length of California, is the boundary between two of the plates that make up the earth's surface. Earthquakes along this fault are due mainly to stresses that accumulate as the plate underlying the Pacific Ocean slides slowly to the northeast.
In 1972, scientists installed a network of laser-based sensors to measure these stresses. For the first six yers, compression along the fault grew steadily. But last year, scientists noticed that the compression had begun to relax, and by October two-thirds of the compression accumulated since 1973 had disappeared.
This seemed potentially dangerous, since one effect of the compression was to hold two edges of the fault together, so that a sudden slip and the resulting earthquake were less likely.
Barry Raleigh of the U.S. Geological Survey said recent data from the Palmdale, Calif., area, where the relaxation appeared greatest, show that compression has begun again, possibly a hopeful sign. But Jim Savage, also of the survey, said relaxation and compression may simply go in cycles and the potentially dangerous relaxation could begin again "within a year of so."