Humans have long observed the effect of the Moon’s gravitational force on the ocean tides. it turns out that the Earth has a gravitational effect on the Moon as well. Earth gravitation is shaping formations of cliffs that form as the Moon slowly shrinks, reports C/Net.

The core of the Moon is cooling. As the core cools, the partially molten regions in mantle solidify and the Moon shrinks slightly, a process that wrinkles the crust. The wrinkles form a type of cliff called “lobate scarps,” usually less than six miles long and tens of yards high.

NASA’s Lunar Reconnaissance Orbiter has identified 3,200 scarps randomly scattered across the Moon’s surface.

“There is a pattern in the orientations of the thousands of faults and it suggests something else is influencing their formation, something that’s also acting on a global scale — ‘massaging’ and realigning them,” explained study lead author and Smithsonian senior scientist Thomas Watters of the National Air and Space Museum in Washington.

That force comes from the gravitational pull of the Earth.

Because the Moon’s core is still cooling, the scarps are likely still forming. Seismic activity is likely to peak when the Earth and Moon are furthest apart. NASA hopes to be able to monitor the hypothesized moonquakes with a lunar seismic network..