Seismic refraction

When I went on a field day with my local geological society on 25 August, we studied several field methods. I've processed my photos of paleoseismic trenching studies and ground-penetrating radar. Today's it's seismic refraction's turn. While we helped set up and record a seismic refraction line crossing the Green Valley fault, I was snapping pictures as well as taking part. But I missed out on the hot 'n' heavy impinger action—I didn't get to bang the wired sledgehammer on the ground.

_{The shooter awaits the signal to impinge — Geology Guide photo}