Monday, March 10, 2014

More preparations: mini seismic experiments

A geophone in grass, awaiting sound waves.

To prepare for our big seismic experiment, we have collected a couple of miniature seismic datasets.  The shallow geology varies substantially along our profile and is very important for planning the depth of drilling and size of our seismic sources. In particular, we need to determine the depth to a limestone layer in a few places.   The same seismic method that we will use to understand the deep geological structures beneath Georgia can also be used at a smaller scale to examine layering in the upper ~100 ft (~30 m) beneath the surface. We recorded the data on 24 geophones attached to a 230-ft-long (70-m-long) cable.  The source was a modified shot gun that looks like a pogo stick.  We drilled small holes in the ground, loaded the gun and stuck it in the hole. To limit the kickback, we weighted the gun down with a metal plate topped by two heavy jugs filled with sand. Hit the plate with a mallet and – BANG – a seismic source! Not a bad way to spend a sunny Sunday!

Check out Dan firing the seismic source...

Donna Shillington
9 March 14