Via Science Daily:

…Earth is not a quiet planet. The key is knowing how to listen to the
ever-present ambient noise. University of Illinois seismologist
Xiaodong Song and graduate student Zhen J. Xu have become good
listeners, especially to the sounds beneath our feet.

Using a technique called “ambient noise correlation,” Xu and Song
have observed significant changes in the behavior of parts of Earth’s
crust that were disturbed by three major earthquakes….