Researchers revisited moonquake data gathered by the Apollo lunar missions during 1969-1977.

Re-examination of the data includes new algorithms to identify the origin of the moonquake that occurred at the moons shallow depths. After mapping the seismic data to satellite images of thrust faults or scarps on the lunar surface which can be seen on the NASA's Lunar Reconnaissance Orbiter, it was discovered that 25% of the moonquake is not due to the asteroid impacts or the activities inside the moon but it was caused by the faults generated.

The four Apollo mission seismometers were studied and analyzed again by scientist which include 28 moonquakes that have an equivalent magnitude on earth of 2 and 5. The study was done using new algorithms to estimate the epicenters and then compared the coordinates to scarp locations in LRO images as stated in the study. It was observed that among the quakes occurred, six of it was in or near apogee wherein the moon orbital point is farthest from earth. According to the scientist, an apogee entails an additional gravitational stress which exerts extra pull on the moon's crust and thrust faults therefore initiating a moonquake. Moreover, eight of the moonquake is said to fell within 19 miles or 31 kilometers of thrust fault which is considered as the basis of the quake.

Another mystery for the scientists are the scarps. The observed scarps that are found to spread across the moon surface are estimated to be more than 50 million years old and it appears that the scarps occurred when the moon's interior cooled down and cause the crust to contract. On the other hand scientists are still curious if scarps have something to do with lunar tectonics, according to Nasa.

LRO photos showed images that include fresh tracks showing tumbled boulders and landslides near the thrust faults. Brighter spots represent disturbances which implicates that the fault is still active because of the moon's continues contraction, reported by the authors. With the obtained LRO images it only indicates that lunar shrinkage is still happening, dragging on the scarps and hurling moonquakes.



This visualization of Lee Lincoln scarp is created from Lunar Reconnaissance Orbiter photographs and elevation mapping. 
Credits: NASA/Goddard/SVS/Ernie Wright

"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," said by Nicjolas Schmerr, co-author and assistant professor of geology at the University of Maryland.

"We learned a lot from the Apollo missions, but they really only scratched the surface. With a larger network of modern seismometers, we could make huge stride in our understanding of the moon's geology. This provides some very promising low-hanging fruit for science on a future mission on the moon" he said

He also added that even though there is so much to be discovered from the Apollo data, this is another call to visit again the moon.