Study recommends distributed acoustic sensing to detect moonquakes

A study from Caltech suggests deploying distributed acoustic sensing on the Moon to detect lunar quakes with greater precision than conventional seismometers.

Seismometers were flown to the Moon during the Apollo mission where they collected data on lunar seismic activity for eight years and recorded quakes as powerful as magnitude 5.

The Moon is not tectonically active, but quakes occur under several circumstances. According to Caltech, some are caused by day-to-night thermal differences as the surface varies in temperature, others that occur deeper could be caused by Earth's gravitational pull, and others are caused by the Moon slowly cooling and contracting over time.

Understanding how, when, and where these quakes occur is critical for planning missions to the Moon, particularly if NASA’s Artemis mission – which will deploy seismic sensors - is to establish a permanent base there for missions to Mars.

Now, a new study demonstrates that distributed acoustic sensing (DAS), an emerging new seismological technology, would measure lunar quakes with extraordinary precision. The research is detailed in Earth and Planetary Science Letters.

Professor of Geophysics Zhongwen Zhan has spent 10 years developing DAS, which involves sending lasers through a fibre optic cable and measuring how the laser light changes throughout the cable as it experiences shaking or tremors.

The cable acts as a sequence of hundreds of individual seismometers, allowing researchers to measure quakes very precisely. A recent study showed that a 100km stretch of cable could function as the equivalent of 10,000 seismometers.

With only a few individual seismometers far apart from each other on the Moon, the seismic signals of lunar quakes are quite noisy. This is due to scattering, where seismic waves become less clear when travelling through the powdery upper layer of the Moon's surface. Having multiple sensors would help clarify a noisy signal.

In the new study, led by Qiushi Zhai, a postdoctoral scholar research associate in geophysics, the researchers deployed a fibre optic cable equipped with DAS technology in Antarctica where the DAS sensors were sensitive enough to measure the small shaking caused by ice cracking and moving, suggesting that they would be able to measure moonquakes.

"Another advantage of using DAS on the Moon is that a fibre optic cable is physically quite resilient to the harsh lunar environment: high radiation, extreme temperatures, and heavy dust," Zhai said in a statement.

The next steps are to demonstrate that DAS can operate with the limited power resources available on the Moon and to conduct more modelling and analysis to understand how small and distant quakes can be and still be detectable.