Passive seismic

Passive seismic is the detection of natural low frequency earth movements, usually with the purpose of discerning geological structure and locate underground oil, gas, or other resources.

[1] Usually the data listening is done in multiple measurement points that are separated by several hundred meters, over periods of several hours to several days, using portable seismometers.

The conclusions about the geological structure are based on the spectral analysis[2] or on the mathematical reconstruction of the propagation and possible sources of the observed seismic waves.

Reliability of the time reverse modelling can be further increased using results of reflection seismology about the distribution of the sound speed in the underground volume.

For instance, during Apollo missions, the Passive Seismic Experiment sensors were deployed that detected lunar "moonquakes" and provided information about the internal structure of the Moon.