It may be hard to believe, as it tugs your body upon the bathroom scales into the danger zone, but gravity is one of the weaker forces of nature. We perceive it as strong only because of the huge size of the earth. Nevertheless, even the moon has a measurable effect on the earth despite its relatively small size. That the oceans' tides are largely an effect of the moon's gravitation is widely known; that tides affect the supposedly solid ground much less so.
Now, we're talking about a very subtle effect, not at all obvious
to those of us parked on the earth's surface. Nevertheless, such earth-tidal
stresses now have been shown to be sufficient to trigger earthquakes under the right
conditions. Now, likely an instability great enough to be set off by the weak lunar
tide would occur soon anyway. However, for those of you who, by nature, enjoy being the
nervous type, keep in mind that the Rio Grande Valley, where so many of us live, is a
rift valley, tore asunder by earthquakes galore.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.