The Microtremor Survey Method use Microtremor observation to distill surface wave, obtain it's dispersion curve and then get inversion to the underground structure.
They can move through scrub or tall grass without making a sound and without showing a sign except, if your eyes are good, an occasional stirring in the vegetation.
1 told him that 1 knew even less than he did.Nestor sighed and seemed truly concerned;he moved his hands and his mouth nervously as if he were on the verge of saying something important and did not know how.