What process causes the powerful, erratic shallow moonquakes occurring less than 20 km beneath the lunar surface?
Answer
The ongoing contraction of the Moon as it slowly cools from the interior outward.
Shallow moonquakes, which are characterized by being more powerful and erratic than deep ones, are specifically attributed to the slow, continuous shrinking of the Moon’s interior. As the interior contracts, it exerts tremendous compressional stress on the overlying brittle crust. This squeezing action leads to fracturing and the formation of thrust faults, which are the manifestations of these seismic events. This contraction process is a direct result of residual internal heat loss occurring over vast timescales, causing the overall volume of the Moon to decrease slightly.
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