What’s Shaking?

As NASA makes plans for another trip the moon, a possible permanent base there, and a link for a prospective manned mission to Mars, it may be in for a bit of a shock … or aftershock. According to Clive R. Neal, professor of civil engineering and geological sciences, the moon is seismically active. In fact, a relatively large number of “moonquakes” have been recorded.

Neal and a team of planetary geologists reexamined data from seismometers placed by Apollo astronauts from 1969 through 1972 (Apollo missions 12, 14, 15, and 16). They identified four types of moonquakes: deep moonquakes, which occur at roughly 700 kilometers below the surface and seem to be triggered by the effect of Earth’s gravity; thermal quakes, which are caused when the “morning” sun strikes the moon’s crust after a lunar night (which is two weeks long); vibration quakes, caused from the impact of meteorites; and shallow quakes, which occur 20 to 30 kilometers below the surface.

Shallow quakes appear to be the most powerful and long-lasting, up to 10 minutes in some cases. “A few of them,” says Neal, “registered 5.5 on the Richter scale, which would move heavy furniture and crack plaster if they occurred on Earth.” The team has not yet identified what causes the shallow moonquakes or where they occur, because the Apollo seismometers were placed in a small area on the front side of the moon.

Neal believes that before proceeding with construction of a permanent lunar base NASA needs to gather more data as well as develop building materials that are flexible enough to withstand the stress of moonquakes.

For more information about moonquakes, click here.