“It’s the trains!” Ryan Hollister yelled to his wife Laura as he burst into their home in Turlock, California. For two weeks in 2017, they’d been staring at data from their newly installed Raspberry Shake, a Raspberry Pi-powered instrument that detects how the ground moves at a specific location. Expecting to see the tell-tale wiggles of distant earthquakes, they instead saw peculiar cigar-shaped waveforms at regular intervals. “The biggest challenge,” says Laura Hollister, “was the noise.”

“I thought it was the toilet flushing or the washing machine,” says Ryan Hollister, but simple tests of going to the restroom or doing the laundry proved him wrong. While stuck in his car watching a train rattle through Turlock, he realized the three tracks that criss-cross this small California town could be causing this mystery seismic noise. As soon as he got home, he pulled up the Raspberry Shake’s data. Sure enough, each weirdly intense caterpillar of seismic waves corresponded to a train, with the highest-amplitude waves correlating with the nearest track’s schedule, only a half mile from home.

It wasn’t the last time that their seismic listening device picked up signs of human activity. As COVID-19 engulfed our world, the Hollisters, a husband-wife team of Earth science educators, noticed that their Raspberry Shake registered much lower levels of activity than usual. The drop was pronounced at times when their street, a main artery to the local high school, should have been pulsing with teenagers.

That change was far from limited to Turlock. Thomas Lecocq, a seismologist who pays particular attention to Earth’s ubiquitous vibrations, discerned a marked decrease in high-frequency noise on a permanent seismic station under his purview at the Royal Observatory of Belgium. This peculiar hush was quieter and longer than the one he’d seen during the subdued days between Christmas and New Year and coincided with his country’s lockdown.

In the following months, Lecocq and 76 coauthors from around the world combed through data from seismic stations spanning more than 70 countries using Python code Lecocq wrote specifically for this purpose. A total of 268 stations had usable data, and 185 of them saw high-frequency seismic noise plummet by up to 50 percent in urban regions. The changes came in lockstep with each country’s closure in response to COVID-19. As the signals from driving, construction, and even walking fell away, Ian Nesbitt, one of Lecocq’s coauthors says, “We may be able to investigate [geologic] signals that we previously couldn’t see because it was masked by that noise.”

Many of the stations were high-end research instruments installed by university or government scientists. But 65 were tiny Raspberry Shakes, sitting in the homes and offices of scientists and hobbyists alike. It turns out that when humans make a lot of noise, seismically speaking, anyone with a spare Raspberry Pi and a few hundred dollars for a Raspberry Shake circuit board and some sensors can see it.

Build your own seismic station

The basic recipe for a seismic station requires four ingredients: sensors to measure Earth’s motion, a means to record the measurements, a long-term storage solution (either local or elsewhere), and a power source, says Emily Wolin, Seismic Network Manager for the U.S. Geological Survey (USGS) Albuquerque Seismological Laboratory.

State-of-the-art seismic stations boast numerous sensors that detect an immense range of frequencies, capturing Earth’s movement in three directions—up-down, east-west, and north-south. Digitizers and data loggers precisely record and time stamp the data. To power the equipment, the most remote stations may use solar panels, with power requirements varying dramatically based on communication needs, says Wolin.

To add a new seismic station to an earthquake monitoring network, Wolin says scientists must scout locations that take into account regional geology and possible noise sources—like railroads (the Hollisters' home would have never made the cut). With a list of candidate sites, they then identify and contact landowners for permission and secure access for construction, installation, and subsequent maintenance.

Wolin explains that sometimes, preparation may involve “hiring a drill rig to bore hundreds of meters into solid rock.” In some instances, thermally sealed and waterproof seismic vaults must be carefully constructed to house equipment so sensitive that they would otherwise pick up minuscule changes in pressure and temperature. Vaults also help minimize pesky anthropogenic noise. To install the sensor and electronics, “it’s not rocket science,” says Sue Hough, a USGS seismologist, but “it does take special training.”

Each layer of complexity adds another line to the bill. According to Hough, top-tier versions of a seismic station can cost well over $10,000, excluding installation costs. Branden Christensen, CEO of Raspberry Shake, says that when those costs are included, installing a single seismic station could cost upwards of $100,000. Those prices are exclusively affordable to government agencies, research institutions, and industry.

Raspberry Shakes, on the other hand, have basic versions of the same components at a fraction of the price. A Raspberry Shake circuit board costs as little as $100, and it plugs into almost any ethernet or wireless-enabled Raspberry Pi. “We thought that people would have [Raspberry Pis] sitting around in their drawers,” says Christensen, “and we [designed Raspberry Shakes to] support them all.”

A seismic sensor, like a geophone, plugs into the Raspberry Shake board, which serves as an amplifier and digitizer. The sensor’s output comes in the form of voltage differences that must be amplified and converted into a known voltage per velocity. This conversion, called a gain, leaves the output in voltage units, according to Nesbitt, who is also Raspberry Shake’s former chief scientist.

The Raspberry Shake digitizes this information and pipes it to the Raspberry Pi for further processing and archiving. An 8 gigabyte microSD card, which Nesbitt describes as the hard drive of the Raspberry Pi, ships with every Raspberry Shake and comes pre-loaded with all of the Shake software. The Raspberry Pi houses the SD card and provides power for the entire seismic station. “[The Raspberry Pi] is the computer underlying everything,” says Nesbitt.

With a Raspberry Shake board, building your own seismic station from scratch becomes as simple as adding a sensor and plugging the Raspberry Pi into your wall socket, although Christensen recommends crafting an enclosure (you can use Lego bricks!) to protect it from the bumps of the denizens of your household.

If you’d rather not assemble your own from scratch, Raspberry Shake makes several turnkey options based on the number and type of sensors you want. Turnkey options, Hough says, pack all these components into a compact plexiglass box.

The Hollisters chose the turnkey Raspberry Shake 4D, which can be had for under $400. To install, Ryan Hollister says all they needed to do was, “level it and point the axes in the right direction so it’s oriented properly, and plug it in.” Easy as, well… pi(e).