Anyone ever had people come by their house for "seismic test readings"?? I'm in central OK.

These guys have been going all over town putting these little white things in yards, and driving these trucks around doing whatever they do. They just stopped by my house to inform me they're doing testing and naturally I was curious so I watched. The trucks put a big weight looking thing down and shake the ground creating a mini earthquake feeling, enough to shake the house a little, and then drive away. I know we've been getting more earthquakes than usual here in Oklahoma, but I'm nearly 30 and they've never tested anything like this before. It's a little weird. Probably nothing, but curious if anyone from places like California or something where they have many more earthquakes know what they are doing? Like what kind of information are they trying to get? They told me nothing other than they were "doing a test" and would be gone in a minute. Lol. Not much to go on.

I'll try to attach pictures and a video.

[link to scontent-dft4-1.xx.fbcdn.net (secure)]


I can't figure out the video, but basically it's just that truck on the left shaking the ground with the big metal thing thats on the center bottom of his truck.

So...what are they trying to figure out since no one around here seems to know and they wouldn't tell me?