Dangerous Footsteps & the Seismograph

This is a seismograph on our property. Why is it here?

The quarry behind our house.

They occasionally blast from spring through fall and yesterday was another blast day. In 2005, the last blast of the year shook the trailer so hard, if felt like an earthquake hit. After that, we became concerned about our concrete floor and well cracking. Especially after part of the bank around the house caved in.

Today they brought the seismograph to measure how much ground vibration we get. Here's an up-close picture.

Now I figured that there would be a long spike driven into the ground to test shock waves, so I was surprised to find out differently. It's not that rod on the left that's measuring the waves (I think that measures location/distance--land profiling). It's that round silver thing attached to the chord on the right.





There's no long rod on the bottom, either. I'm not sure if it's the three prongs that measures vibrations or the hole. It kind of reminds me of a baby monitor nurses strap onto the belly when a woman's in labor. Without the prongs, of course. (Youch!)




This dude here reading the tape is the head blaster for the quarry. He's with Green Mountain Explosives. They've got some cool info and pictures on their website about drilling, explosives and equipment. Check them out.


If I have my info right, this other dude here is in charge of the quarry. He says he "sells dirt for a living." They're looking so intently at the tape because the seismograph registered 91 times. 91! The head blaster looked at us and said, "Were you walking around a lot?"

Um, we weren't supposed to walk??? It would've been nice to know that before the blast.

It turns out someone else had set the sensitivity level lower by a couple of points. It might have been picking up footsteps, the haying machine in the field 75 feet away, or the trucks in the pit as they rumbled through. It didn't matter, though. All 91 readings were low and nothing to be concerned about, and blast air waves shaking the trailer won't harm our construction.

Our foundation and well should be safe. That is, if the many footsteps around here don't get them first.