It could be that the moon's influence is harder to pinpoint, he speculated. Like the tides of the oceans, the land masses of the Earth also have tides--though far less pronounced--as the ground flexes in accordance with the pull of the moon and the sun. But the most notable effect of lunar gravity is on the oceans, where tidal fluctuations are well known.
Not a Prediction
Kilston and Knopoff emphasized during interviews that, while their studies do show a correlation between major earthquakes and lunar and solar cycles, they are not making a prediction.
Still, their paper in the journal Nature nearly three years ago made it clear that Southern California may have entered a very interesting period, especially as the "maximum lunar declination" approaches in November, 1987.
The paper stated:
"A literal extrapolation of our observations implies that during a window of a few years width astride this date, at times near full or new moon, and near sunrise or sunset, one might be more likely than otherwise to observe one or more large earthquakes in Southern California."
DO THE SUN AND MOON TRIGGER EARTHQUAKES?
Studies suggest the gravitational pull of the moon and sun may trigger major earthquakes in Southern California along faults that run in a north-south direction. The two bodies, when aligned, may pull faults apart, thus relieving friction and setting off quakes. If so, Southern California should expect a major quake some time over the next three or four years.
During a full moon, the sun and moon are aligned on opposite sides of faults, such as the San Andreas, that run north to south. Studies suggest they may pull the fault apart slightly, triggering major earthquakes.
During a new moon, the sun and moon are aligned on the same side of the fault, and their gravitational pull could tend to lift the land on that side of the fault, thus reducing the friction that keeps the fault from slipping.