Corrected entry: When Val and Earl meet Rhonda for the first time she asks if there is any drilling, explosions etc. and they say no. She explains the graph's readings are strange and thought it could be because of possible works going on. A bit later as Val and Earl are leaving Perfection they come across 2 workmen drilling the road.
Greg Dwyer
10th Jun 2018
Correction: The small jackhammers the road workers are using are highly unlikely to be able to affect a distant seismograph. She meant things like oil or deep core drilling. In addition, it's quite possible Val and Earl didn't even know about the road workers.
Greg Dwyer