Our Moon is getting cooler, causing it to shrink. Now, research published in Nature Geoscience on Monday suggests that shrinkage is leading to a whole lot of shaking going on, with a little help from Earth too.
A team of geologists believe these cliff-like features are evidence of lunar tectonic activity. They analyzed seismic data taken from 28 moonquakes recorded during 1969 and 1977 during the Apollo missions with a type of algorithm known as a sparse seismic network.
By looking at the size and location of the tremors, the algorithm estimates the epicenter of the moonquakes. The researchers mapped these focal points and compared them to faults lines spotted by the NASA’s Lunar Reconnaissance Orbiter (LRO) and found that eight of the moonquakes were caused by the movement of crustal plates along the faults rather than from asteroid impacts.
“We found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the LRO imagery,” said Nicholas Schmerr, co-author of the research paper and an assistant professor of geology at the University of Maryland in the US.
“It’s quite likely that the faults are still active today. You don’t often get to see active tectonics anywhere but Earth, so it’s very exciting to think these faults may still be producing moonquakes.”
Astronauts placed five different seismometers during the subsequent Apollo missions from Apollo 11 to Apollo 16. Each of the magnitudes of the 28 moonquakes would register as somewhere between two and five on the Richter scale if they had been carried out on Earth.
Six out of the eight tectonically active moonquakes occurred when the Moon was at or close to its apogee, the point where it’s most distant from Earth and where the diurnal and recession stresses create the most compression near the tidal axis. This makes it easier for the Moon’s crust to slip along the thrust faults.
“We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active,” said Thomas Watters, lead author of the paper and a senior scientist at the Smithsonian Institution. ®