THUMP AND STACK

The process of collecting the data was pretty simple. Thump the thumper ten times in the same spot, and then move on. The recording equipment was able to add up the signals from multiple thumps. This is referred to as stacking the data.

Most of the shot locations where the thumping was done were inside the fenced-in area, but there were a few locations beyond the ends of some of the lines of sensors.

The recording equipment was two Geometrics units. One model a StrataVisor, and the other a SrataView. They ran off of 12 Volt batteries, and could be used with the built-in display, or with an external display and keyboard. The data was written to internal disk drives, which were downloaded and backed up at the end of the day. The four orange cables in the picture below were the ones that carried the signals from the cables with the geophones connected. I knew the unit on the right personally. We spent a few months together in Antarctica.

We set up shop in a corner of one of the equipment trailers on the site. It was nice to have an air-conditioned place to work for a change. Of course the air-conditioner had to be off during shooting to prevent the noise that it generated from being picked up by the geophones. Just my luck.

Each time the thumper thumped it triggered the recorders to begin recording for 5 seconds. Once the 5 seconds were up the results were displayed. Below is a typical result that we saw from, in this case, a stack of 4 thumps. Increasing time is measured down the display. Each vertical trace, or wiggle, corresponds to a geophone. The 'arrowhead' pattern had to do with the order of the geophones, and the way the geophone cables "snaked" their way back and forth across the site. The six lines that don't look like the others (no, we were not watching Sesame Street) were locations where no geophones were installed for one reason or another.



DIRECT LINKS TO PAGES:
A QUICKIE IN KIRTLAND
THAT'S A FACT
SENSORS FROM HELL
THIS WASN'T A BAMBI MOVIE...
THUMP AND STACK
CAN'T WIN 'EM ALL
THE QUICK AND THE DONE

2018-02-08