LACIE SILVA – Editor
During the U.S. Apollo missions from 1969 to 1977, seismographs were strategically deployed at six locations on the Moon. These instruments detected a notable number of moonquakes annually, ranging from 600 to 3,000, although the majority of these seismic events were characterized by relatively small magnitudes. The comprehensive monitoring during this period significantly contributed to our understanding of the Moon’s geological activity and structure.
There are four types of moonquakes: deep (~435 miles below the surface), shallow (~31–137 miles below the surface), thermal, and foreign impacts. Notably, events triggered by impacts such as lunar modules, booster rockets, and meteorites were detected at distances exceeding 600 miles from seismograph stations. Deep and shallow moonquakes are believed to stem from natural sources within the Moon’s interior, likely associated with rock fracturing, a phenomenon akin to seismic activity on Earth. The prevailing type of natural moonquake features deep foci, situated at depths ranging from ~373 to 622 miles, while the less common variety exhibits shallower focal depths.
The lunar surface’s minimal ground noise, in contrast to Earth, allowed for the operation of seismographs at exceptionally high magnifications during the Apollo missions. With multiple stations on the Moon, the arrival times of P and S waves from moonquakes were leveraged to determine earthquake foci, mirroring methods used on Earth. P waves, or primary waves, characterized by faster movement, serve as the initial signals upon a quake’s arrival. Conversely, S waves, also known as secondary waves, exhibit lateral movement in a sine wave pattern perpendicular to the wave’s direction. These details highlight the lunar seismic exploration’s capacity to provide valuable insights into the Moon’s subsurface dynamics.
The Marion Tribune – January 18, 2024
