“It’s the trains!” Ryan Hollister yelled at his wife Laura as he stormed into their Turlock, California home. In 2017, they spent two weeks looking at data from their newly installed Raspberry Shake, a Raspberry Pi-powered instrument that detects how the ground is moving in a specific location. They expected to see the telltale movements of distant earthquakes, but instead saw peculiar cigar-shaped waveforms at regular intervals. “The biggest challenge,” says Laura Hollister, “was the sound.”
“I thought it was the toilet flush or the washing machine,” says Ryan Hollister, but simple tests of going to the toilet or doing laundry proved him wrong. While he was trapped in his car, watching a train rattle through Turlock, he realized that the three tracks crossing this small California town could be creating this mysterious seismic sound. As soon as he got home, he pulled out the Raspberry Shake data. Sure enough, each strangely intense track of seismic waves corresponded to a train, with the waves with the highest amplitude correlating with the schedule of the closest track just half a mile from home.
It wasn’t the last time their seismic listening device picked up signs of human activity. As COVID-19 swept our world, the Hollisters, a husband-and-wife team of Earth science educators, noticed their Raspberry Shake registered much lower activity levels than usual. The drop was pronounced at times when their street, a main artery to the local high school, should be teeming with teenagers.
That change was far from limited to Turlock. Thomas Lecocq, a seismologist who pays particular attention to the Earth’s ubiquitous oscillations, noted a marked decrease in high-frequency noise at a permanent seismic station under his jurisdiction at the Royal Observatory of Belgium. This peculiar silence was quieter and longer than the one he’d seen during the subdued days between Christmas and New Years, and coincided with the lockdown of his country.
Over the following months, Lecocq and 76 co-authors from around the world combed through data from seismic stations in more than 70 countries using Python code Lecocq wrote specifically for this purpose. In all, 268 stations had usable data, and 185 of them saw high-frequency seismic noise drop by up to 50 percent in urban regions. The changes coincided with the shutdown of each country in response to COVID-19. When the signals of driving, building and even walking faded, Ian Nesbitt, one of Lecocq’s co-authors, says: “Maybe we can investigate [geologic] signals that we couldn’t see before because it was masked by that noise.”
Many of the stations were high-quality 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 people make a lot of noise, seismically speaking, anyone with an extra 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 solution for long-term storage (local or elsewhere), and a power source, said Emily Wolin, Seismic Network Manager for the US Geological Survey (USGS) Albuquerque Seismology Laboratory.
State-of-the-art seismic stations have numerous sensors that detect a huge range of frequencies and record the movement of the Earth in three directions: up-down, east-west and north-south. Digitizers and data loggers accurately record the data and provide a time stamp. To power the equipment, the most remote stations can use solar panels, with power requirements varying widely based on communication needs, Wolin says.
To add a new seismic station to an earthquake monitoring network, Wolin says scientists should explore sites that take into account regional geology and potential noise sources, such as railroads (the Hollisters’ home would never have made it). With a list of candidate sites, they identify and contact landowners for permission and secure access for construction, installation and subsequent maintenance.
Wolin explains that the preparation can sometimes involve “renting a drilling rig to drill hundreds of meters into bedrock.” In some cases, thermally sealed and watertight seismic vaults must be carefully constructed to house equipment so sensitive that they would otherwise absorb minute changes in pressure and temperature. Safes also help minimize annoying anthropogenic noise. Installing the sensor and electronics, “it’s not rocket science,” says Sue Hough, a USGS seismologist, but “it does require special training.”
Each layer of complexity adds a new line to the bill. According to Hough, top versions of a seismic station can cost upwards of $10,000, not including installation costs. Branden Christensen, CEO of Raspberry Shake, says that if those costs are factored in, installing a single seismic station could cost more than $100,000. Those prices are affordable only to government agencies, research institutions and industry.
Raspberry Shakes, on the other hand, have basic versions of the same components for a fraction of the price. A Raspberry Shake PCB costs just $100 and plugs into almost any ethernet or wireless Raspberry Pi. “We Thought People Would Have” [Raspberry Pis] sitting in their drawers,” Christensen says, “and we… [designed Raspberry Shakes to] support them all.”
A seismic sensor, such as a geophone, connects to the Raspberry Shake board, which acts 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 speed. This conversion, called a gain, leaves the output in units of voltage, according to Nesbitt, who is also the former Raspberry Shake chief scientist.
The Raspberry Shake digitizes this information and sends it to the Raspberry Pi for further processing and archiving. An 8 gigabyte microSD card, which Nesbitt describes as the Raspberry Pi’s hard drive, comes with every Raspberry Shake and comes preloaded with all Shake software. The Raspberry Pi houses the SD card and provides power for the entire seismic station. †[The Raspberry Pi] is the computer that underlies everything,” says Nesbitt.
With a Raspberry Shake board, building your own seismic station from scratch becomes as easy as adding a sensor and plugging the Raspberry Pi into your wall outlet, although Christensen recommends making an enclosure (you can Use Lego bricks!) to protect it from the knocks of the inhabitants of your household.
If you’d rather not build your own sensor from scratch, Raspberry Shake makes several ready-made options based on the number and type of sensors you want. Ready-made options, Hough says, package all of these components in a compact Plexiglas box.
The Hollisters opted for the ready-to-use Raspberry Shake 4D, which can be had for under $400. To install, Ryan Hollister says, all they had to do was “level it up and point the axes in the right direction so it’s oriented properly, and plug it in.” Easy if, well…pi(e).