New Analysis Shows the Moon Is Tectonically Active

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Thousands of young cliff-like, fault scarps detected in images taken by NASA’s Lunar Reconnaissance Orbiter Camera (LROC) are evidence of a shrinking moon and recently active lunar faults. But just how recently these faults were active was not known. The Apollo astronauts placed seismometers on the moon that recorded shallow moonquakes, but the source of these quakes was also not known. New analysis of Apollo seismic data shows that some shallow moonquakes can be linked to young faults. This is evidence that the moon, like Earth, is tectonically active. The analysis is explained in “Shallow Seismic Activity and Young Thrust Faults on the Moon,” a paper by lead author and Smithsonian senior scientist Thomas R. Watters, published in the May issue of Nature Geoscience.

Taurus-Littrow valley is the location of the Apollo 17 landing site (asterisk). Cutting across the valley, just above the landing site, is the Lee-Lincoln fault scarp (arrows). Movement on the fault was the likely source of numerous moonquakes that triggered events in the valley. 1) Large landslides on of slopes of South Massif draped high albedo regolith on and over the Lee-Lincoln scarp. 2) Boulders rolled down the slopes of North Massif leaving tracks or narrow troughs in the regolith on the slopes of North Massif. 3) Landslides on southeastern slopes of the Sculptured Hills. Credit: NASA/GSFC/Arizona State University/Smithsonian

“It’s a great testament to the continued benefits of the Apollo program that seismic data collected over 40 years ago is helping to confirm that the moon is likely tectonically active today,” Watters said. “The connection between the location and timing of shallow moonquakes and known young faults is further evidence that our moon is a dynamic world.”

Watters is a scientist in the Center for Earth and Planetary Studies at the National Air and Space Museum and a co-investigator on the LROC.

Shallow moonquakes, like earthquakes, are expected to cause significant ground motion as seismic wave radiate outward from the source. This seismic shakemap shows the expected round motion for a slip event on a thrust fault (red line) associated with the Mandel’shtam scarp. The shakemap showing peak vertical acceleration for a moonquake of magnitude 6.36 Mw hypocenter at a depth of 350 m. Shades of blue, green, and white indicate areas where shaking is strong. The regional topography is shown by the white contour lines (500 m contour interval). Credit: University of Maryland/Smithsonian

The Apollo 11, 12, 14, 15 and 16 astronauts placed seismometers—instruments that measure the shaking produced by quakes—at their landing sites. Four of the seismometers operated from 1969 to 1977 and recorded 28 shallow moonquakes. Watters is lead author of the study that analyzed data from these seismometers using an algorithm, or mathematical program, developed to pinpoint quake locations detected by a sparse seismic network. The new analysis gave a better estimate of the moonquake locations.

Using the revised location estimates, the team found that eight of the 28 shallow quakes were within 30 kilometers (18.6 miles) of faults visible in lunar images. This is close enough to tentatively attribute the quakes to the faults, since modeling by the team shows that this is the distance over which strong seismic shaking is expected to occur, given the size of these fault scarps.

The lobate scarps are formed when the lunar crust is pushed together as the Moon contracts. This causes the near-surface materials to break forming a thrust fault. The thrust fault carries crustal materials up and sometimes over adjacent crustal materials. Slip events on the thrust fault trigger shallow moonquakes that can cause strong seismic shaking many tens of kilometers away from the scarp. Credit: Arizona State University/Smithsonian

“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,” Watters said.