To understand what the Raspberry Shake seismograph is and how it works, we must start by gaining an understanding of what seismology and seismic waves are. So, we will start with the question:
What is seismology?
Seismology is the study of seismic waves, waves of acoustic energy that travel through the earth. Like sound waves, seismic waves can be measured. We can measure sound waves with microphones, and we can measure seismic waves with seismographs.
Natural seismicity is caused by events such as earthquakes, volcanic activity, and extreme weather events. Man-made (anthropogenic) seismicity can be caused by events like construction work, explosions, traffic, and fracking.
What are seismographs and how are they used?
A seismograph is a device that detects and records ground movement. The sensor, called the seismometer, is a suspended mass that remains still until the Earth moves. As the mass moves, it sends analog data to a “digitizer”. This converts the data into frequency and amplitude, a digital signal. Data is then transformed by a digitizer which translates motion into a digital image that can be seen on a computer monitor.
Seismographs can detect ground motion from earthquakes to a car driving near by. Any movement that travels through the ground is picked up by these sensitive devices. For this reason it is common to see “noise” on seismographs in areas with commuter traffic and other human activity.
Around the world, seismographs are used in different industries and areas studying the movement of the Earth. Seismologists use seismic data to locate the epicenter (starting point) of earthquakes. Volcanologists use seismic data to detect underground magma movement, and petroleum geologists use seismic data to discover oil and gas beneath the surface of the Earth.
What about our Shake? What is a geophone?
The Raspberry Shake has two main components: an environmental sensor that measures the ground movement, the geophone, and it also contains an analog-to-digital converter, and the digitizer box.
The main sensor is a geophone. We can think of a geophone as a low-frequency “microphone” for listening to the ground. A geophone works by generating electric signals that represent ground motion (such as earthquakes, or any seismic activity!). These signals are positive (+) and negative (-); they are measured through voltage. We refer to them as “analog” signals.
When you pass a magnet through a coil, an electrical current is generated in the coil. Inside a geophone – a coil is suspended on a spring surrounded by a magnet. As the Earth moves and shakes, the mass rises and falls, passing up and down around the magnet creating a small electrical current. See the geophone diagram in Figure 1 below.
The Raspberry Shake board contains a digitizer, the device that converts the data into a digital signal so that you can see the seismic wave on your computer screen.
Figure 1: Diagram of a geophone and its parts.
How can we use our Shake?
The Shake can be used to measure anything that causes ground vibrations and it can process that data in a variety of ways. The raw seismic data that the Shake records can be seen on s seismic application called SWARM. SWARM also allows users to access all Raspberry Shake seismographs forwarding data to the network. As of today, you can see the data from more than 1000 stations from across the world!
The Shake can also do much more than measure earthquakes. Any ground vibrations are detected by the Shake’s sensitive geophone – your Shake can detect traffic, fireworks, busy streets, strong bass speakers… anything that can cause the ground to vibrate!
For example, the University of Michigan created a “cheer-meter”, to measure which team had the biggest applause during sports games. They created Cheer Magnitude equations and everything! Just imagine the possibilities of use in your classroom and school, outside of an earthquake monitor.