Seismicity in sync with the sun? - link between sun-spots and earthquakes

Science News, April 27, 1985 by Stefi Weisburd

The 11-year cycle in the number of sunspots, as well as the underlying flip of the sun's magnetic field every 22 years, has been tied to many phenomena on earth, including global climate, the production of carbon-14 and the planet's rotation rate. Now Charles Bufe of the U.S. Geological Survey in Reston, Va., suggests that earthquakes -- at least those that rumble in Parkfield, Calif.--be considered for this list too.

The timing of Parkfield earthquakes has been remarkably regular; the last six events with magnitudes 5.5 or higher occurred about every 22 years with the exception of one quake in 1934 that came 10 years ahead of schedule (SN: 4/13/85, p. 228). After comparing the Parkfield record to solar activity over the last century and a half, Bufe found that the Parkfield quakes all fell within 2.4 years of sunspot minima. The probability of producing such a pattern randomly, says Bufe, is less than 1 in 100. Most of the quakes were also in sync with the cycle of the solar magnetic field. Moreover, the 1934 quake, Bufe notes, happened to follow a period of unusually low sunspot activity.

Bufe cautions that the similarity in the Parkfield quake and solar cycles in no way proves that the sun can trigger earthquakes and no one has proposed any possible mechanisms linking the two. but if there is a real link it's clear that it would be very complex, involving changes in the magnetic fields between the sun and earth, changes in the earth's atmosphere and rotation, and changes in the motion of and stresses between the plates that cover the globe.