On February 28, 2001, a magnitude 6.8 earthquake, located some thirty miles below the surface of the earth and a few miles away from Olympia Washington, moved the ground for a bit more than half a minute.
A sand tracing pendulum, located at a shop in Port Townsend called Mind Over Matter (since moved to Sedona, Arizona), produced some very interesting patterns.
Read more about it here.
That’s really cool!