I am pretty sure you are right on the mark there.
I made a habit of listening to the tone modulated seismic transmitters
in southern California and with experience, they definitely sounded
like you would expect if a source was reflecting off of various
impedance discontinuities in the crust which
I live in the San Francisco bay area. You may recall that back in 1989
we had a big earthquake that did a lot of damage.
The epicenter was near Loma Prieta, which became the name for this
earthquake. That is about 60 miles south of San Francisco, yet a lot of
the bad damage occurred there, at