NZ researcher probes lunar 'moonquakes'

Evidence that the moon experiences earthquakes was first collected during NASA's Apollo missions between 1969 and 1972. Photo: NASA

A New Zealand-based researcher is investigating "moonquakes" - a curious lunar phenomenon first discovered by Nasa's Apollo missions.

That the moon experienced earthquakes was first demonstrated by astronauts on five of the Apollo missions between 1969 and 1972, after they placed seismometers at landing sites, recorded the information and radioed it back to Earth.

The data, recording more than 13,000 quakes up until 1977, revealed several kinds of moonquakes: deep moonquakes about 700km below the surface, probably caused by tides, vibrations from the impact of meteorites and thermal quakes caused by the expansion of the frigid crust when first illuminated by the morning sun after two weeks of deep-freeze lunar night.

These types were generally harmless, but a fourth kind, shallow moonquakes striking only 20km or 30km below the surface, could register magnitudes of up to 5.5, powerful enough to move heavy furniture and crack plaster in an Earth setting.

Jesse-Lee Dimech, who is completing his PhD in geophysics at Victoria University, and who also has a postdoctoral role at Nasa, said seismic energy was useful for looking inside planets.

"Using the energy from earthquakes or, in this case, moonquakes, we can gain insight into the composition and structure of the moon."

He was working on categorising and detecting moonquakes using the Apollo seismic dataset, as well as extra datasets not previously used for this purpose.

One of the new techniques he was exploring was "shear wave splitting analysis", a research interest of Professor Martha Savage from Victoria University, who has worked with Dimech to undertake the first shear wave splitting analysis off Earth.

"When seismic waves travel through layers of rock they split in much the same way light does when it hits a crystal," Dimech said.

"By measuring how much splitting occurs, we can infer physical properties from the rock, such as stress and fracturing, the presence of fluids, and rock laminations."

Another technique, developed by Victoria associate professors Richard Arnold and John Townend, is a statistical method of examining the geometry of the faults responsible for earthquakes.

Victoria University researcher Jesse-Lee Dimech is investigating "moonquakes" - a curious lunar phenomenon first discovered by NASA's Apollo missions. Photo: Supplied

"I applied this technique in my PhD to earthquakes we found in the upper mantle - the layer beneath the crust - which was able to tell us what type of faults produced them," Dimech said.

"We will be using a modified version of this code to understand the type of faulting associated with 'deep' moonquakes, which are about halfway between the Moon's surface and its core."

Some of the techniques he uses may also be useful in helping Nasa learn about the composition of Mars when they land a seismometer there in two years as part of the InSight mission.

Australian-born Dimech said he has loved space since he was a child, and a postdoctoral role at Nasa was the culmination of a lifelong ambition.

"I was actually penpals with Australia's first astronaut Andrew Thomas.

"We exchanged several letters when I was a kid, and I even talked to him on the phone once, as well as fellow astronaut John Glenn who just happened to be in the office at the time.

"They definitely inspired me. I was also the youngest member of an astronomy club. I've always been fascinated by Nasa."

The work was being carried out in collaboration with Dr Renee Weber, Dimech's adviser at Nasa, and Dr Brigitte Knapmeyer-Endrun, a scientist at Germany's Max Planck Institute for Solar System Research.

"It's a great opportunity to work with some of the world's top planetary seismologists," he said.

"By applying new seismic analysis techniques we may be able to learn new information about the moon - even from such an old dataset."