“It’s the trains!” Ryan Hollister shouted at his wife, Laura, as he entered their home in Turlock, California. For two weeks in 2017, they have been looking at data from their new Raspberry Shake, a Raspberry Pi-powered tool that detects how the ground moves in a certain location. Waiting to see the telling shocks of distant earthquakes, they instead saw special cigar-shaped waveforms at regular intervals. “The biggest challenge,” says Laura Hollister, “was the noise.”
“I thought it was the toilet or the washing machine,” says Ryan Hollister, but simple tests to go to the bathroom or wash the laundry proved him wrong. While stuck in the car, watching a train shake through Turlock, he realized the three paths that run through this small town in California that could cause this seismic noise mystery. As soon as he got home, he pulled the Raspberry Shake data. Sure enough, each strangely intense caterpillar from seismic waves corresponded to a train, where the highest amplitude being correlated with the schedule of the nearest track, just half a mile from home.
It was not the last time their seismic listening device showed signs of human activity. As COVID-19 swept the world, Hollisters, a husband and wife team of Earth science educators, noticed that Raspberry Shake had much lower levels of activity than usual. The decline was pronounced at a time when their street, a main artery to the local high school, should have hit the teenagers.
This change was far from limited to Turlock. Thomas Lecocq, a seismologist who pays special attention to the ubiquitous vibrations of the Earth, has noticed a significant decrease in high frequency noise on a permanent seismic station under its competence at the Royal Observatory of Belgium. This silent feature was quieter and longer than he had seen in the subdued days between Christmas and New Year and coincided with the blockade of his country.
In the following months, Lecocq and 76 co-authors 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 drop by up to 50% in urban areas. The changes occurred with the closure of each country in response to COVID-19. As signals from driving, construction and even walking fell, Ian Nesbitt, one of Lecocq’s co-authors, says: “We may be able to investigate [geologic] signals I couldn’t see before because it was masked by that noise. “
Many of the stations were state-of-the-art research tools installed by scientists from the university or government. But 65 were tiny Raspberry Shakes, housed in the homes and offices of scientists and amateurs. It seems that when people make a lot of noise, seismically speaking, anyone has a spare Raspberry Pi and a few hundred dollars for a Raspberry Shake circuit board and a few sensors can see it.
Build your own seismic station
The basic recipe for a seismic station requires four ingredients: sensors to measure the Earth’s motion, a means of recording measurements, a long-term storage solution (either local or elsewhere) and an energy source, says Emily Wolin , Seismic Network Manager for the US Geological Survey (USGS) Albuquerque Seismological Laboratory.
State-of-the-art seismic stations boast numerous sensors that detect a huge range of frequencies, capturing the Earth’s motion in three directions – up-down, east-west and north-south. Digitizers and data logs accurately record and stamp data. To power the equipment, the most remote stations can use solar panels, with energy requirements that vary dramatically depending on communication needs, says Wolin.
To add a new seismic station to an earthquake monitoring network, Wolin says scientists need to research locations that take into account regional geology and possible sources of noise – such as railroads (Hollister House would never have done cutting). 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 sometimes training can involve “hiring a drilling rig that allocates hundreds of meters of solid rock.” In some cases, heat-sealed and waterproof seismic vaults must be carefully constructed to house equipment so sensitive that it would otherwise take on tiny changes in pressure and temperature. Safes also help minimize tiring anthropogenic noise. To install the sensor and electronic devices, “it’s not rocket science,” says Sue Hough, a USGS seismologist, but “it requires special training.”
Each layer of complexity adds a different line to the bill. According to Hough, the top versions of a seismic station can cost well over $ 10,000, excluding installation costs. Branden Christensen, CEO of Raspberry Shake, says that when these costs are included, installing a single seismic station could cost more than $ 100,000. These prices are available exclusively 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 only $ 100 and connects to almost any Raspberry Pi compatible with Ethernet or wireless. “I thought people would have [Raspberry Pis] sitting in their drawers, “says Christensen,” and us [designed Raspberry Shakes to] support them all. “
A seismic sensor, like a geophone, connects to the Raspberry Shake board, which serves as an amplifier and digitizer. The sensor output comes in the form of voltage differences that must be amplified and converted to a known voltage at speed. This conversion, called gain, leaves the output in voltage units, according to Nesbitt, who is also the former Raspberry Shake scientist.
Raspberry Shake digitizes this information and transmits it to the Raspberry Pi for further processing and archiving. An 8 gigabyte microSD card, which Nesbitt describes as the Raspberry Pi hard drive, comes with each Raspberry Shake and is preloaded with all the Shake software. The Raspberry Pi hosts the SD card and provides power for the entire seismic station. “[The Raspberry Pi] it’s the computer that drives everyone, ”says Nesbitt.
With a Raspberry Shake board, building your own seismic station from scratch becomes as simple as adding a sensor and connecting the Raspberry Pi to the wall outlet, although Christensen recommends creating a housing (you can use Lego bricks!) To protect it from bumps. . among the inhabitants of your household.
If you prefer not to assemble from scratch, Raspberry Shake makes several turnkey options based on the number and type of sensors you want. Turnkey options, says Hough, wrap all of these components in a compact plexiglass box.
The Hollisters chose the turnkey Raspberry Shake 4D, which can be obtained for less than $ 400. For installation, Ryan Hollister says all he has to do is “level and straighten the axes in the right direction so that they are oriented correctly and connect.” Easy as, well … pi (s).