Down in the basement of Steve Jones’ southeast Huntsville home, just past the electrical workshop, is a door into an unfinished sub-basement.
Here, on a concrete base on a rock outcropping, sits Jones’ latest homemade seismometer inside its sealed plastic pressure case.
Technically, Jones has built a broadband, vertical-sensing seismometer, the same kind used by institutional monitoring stations around the world. Practically, the toaster-sized instrument is the latest fruit of an interest that has brought this NASA electrical engineer from curious hobbyist in 1994 to “advanced amateur” status.
From Huntsville, Jones has monitored earthquakes ranging from the 9.1 to 9.3 magnitude 2004 Indian Ocean tremor, one of the most powerful ever recorded, to the magnitude 2.9 quake in Walker County earlier this month. “We have 2s and 3s all the time,” Jones said of north Alabama. “Everybody does.”
The idea of solid ground is a story we tell ourselves, Jones said. Truthfully, the Earth’s surface is a web of giant plates in constant motion, seeming stable only to humans who can’t feel them move except in the most extreme cases.
“The earth is always moving,” he said. “The planet is like a bell. It’s ringing all the time.”
Friction sticks the floating plates together when they touch, and they stay stuck until, as Jones explains on his website, alabamaquake.com, “the stress buildup on the locked edges overcomes the friction.”
What happens then?
“The sudden shift or breaking of the rock and the release of stored energy creates waves that travel concentrically outward through the earth’s rocky crust.”
That’s what we call an earthquake, and seismic graphs of quakes near and far are on the website.
When a quake will happen can’t be predicted, but where it will happen is better understood. Earthquakes are relatively rare in our region, except for the New Madrid Fault area near the border of Tennessee and Missouri, but they are more common where major geological features meet. That includes California, which sits on a plate between an ocean and mountain chain.
The energy from an earthquake moves through the body of the earth and along its surface in waves. “It’s the surface waves that do the damage,” Jones explained.
Body waves are called compressional or P waves. P means “primary.” P waves compress and expand objects in the path they are traveling.
Shear waves are secondary waves called S waves. They shake the ground up and down.
Following after both P and S waves are surface waves.
On a seismometer graph, the distance between the P and S waves tells a trained observer how far the earthquake was from the monitoring station.
Jones was attracted to the study of earthquakes for two main reasons. It fascinated him that “something on the other side of the world would make the needle move” in Huntsville, and “the big surprise that I could build an instrument that would (capture) it.”
His early seismometers were fairly simple, but the current one is so sensitive that it can capture, on a “quiet” day, up and down earth movement in the hundreds of nanometers. A nanometer is one-billionth of a meter. By comparison, a human hair is 60,000 nanometers thick, Jones said.
“The instrument … is so sensitive that I normally operate it under a light-tight cover that also provides thermal insulation,” Jones said in a follow-up email, “because even the beam of a flashlight shown on it from several feet away can significantly disturb its operation .”
“It’s an interesting hobby,” Jones said, and he’s trying to pass it on. Jones has a presentation for middle school students that he calls Earthquake 101. It explains earthquakes and monitoring them in simple words and graphics.
“I want to educate the kids,” Jones said. They can learn about electronics, mathematics and physics in an understandable way. “If I can help get a kid interested in science, that would be good
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