Seismometers placed on the Moon during the Apollo missions revealed seismic activities on the planet's near side, but the silence prevailing on the far side has perplexed scientists. To comprehend this disparity, researchers from the California Institute of Technology and the Woods Hole Oceanographic Institution propose the installation of an expanded Distributed Acoustic Sensing (DAS) network, comprising detectors and sensors, on the Moon.

The technology relies on the tiny internal flaws in a long optical fiber as seismic sensors. An interrogator at one end of the fiber transmits laser pulses along the cable that are reflected off the fiber flaws and bounced back to the instrument. Analysis of changes in the reflected pulses can reveal more about the resulting seismic waves.

[See also: Using fiber optic cables to signal tsunami events]

A barrier to the detection of seismic waves crucial for unraveling lunar depths is posed by the Moon’s loose layer of rock and mineral fragments, or regolith. To overcome this physical impasse, the researchers advocate use of array stacking signal processing along with data collected by DAS sensors to isolate accurate signals from seismic noise.

When tested using artificial seismograms created from data collected by seismometers deployed by the Apollo missions, the scientists successfully retrieved a seismic wave phase called ScS, which is a shear or S-wave that travels from the earthquake origin toward the Moon’s core before being reflected up to the surface. Based on the study reported in Seismological Research Letters, the team is confident that a fiber seismic network could identify the kind of seismic waves that would provide more information about the Moon’s deep core structure.

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