When an earthquake strikes, it’s usually hard to miss. At least that’s the case with the big ones; the dozens or hundreds of little quakes that go largely unnoticed every day are interesting too, and make sense to track. That’s usually left to the professionals, with racks of sensitive equipment and a far-flung network of seismic sensors. That doesn’t mean you can’t keep track of doings below your feet yourself, with something like this DIY seismograph.
Technically, what [Alex] built is better called a “seismic detector” since it’s not calibrated in any way. It’s just a simple sensor for detecting ground vibrations, whether they be due to passing trucks or The Big One. [Alex] lives in California, wedged between the Hayward, Calaveras, and San Andreas faults in San Jose, so there is plenty of opportunity for testing his device. The business end is a simple pendulum sensor, with a heavy metal bob hanging from a long wire inside a length of plastic pipe. Positioned close to the bob is a copper plate; the bob and the plate form an air-dielectric variable capacitor that controls the frequency of a simple 555 oscillator. The frequency is measured by a PIC microcontroller and sent to a Raspberry Pi, which displays the data on a graph. You can check in on real-time seismic activity in San Jose using the link above, or check out historical quakes, like the 7.1 magnitude Ridgecrest quake in July. [Alex]’s sensor is sensitive enough to pick up recent quakes in Peru, Fiji, and Nevada, and he even has some examples of visualizing the Earth’s core using data from the sensor. How cool is that?
We’ve seen other seismic detectors before, like this piezo-based device, or even one made from toilet parts. We like the simplicity of the capacitive sensor [Alex] used, though.
A geophone is a specially built microphone for listening to the Earth. [JTAdams] found them at a reasonable price so bought some to play with. A geophone is used to detect vibrations from earthquakes, explosions, rumbling trucks, and vibroseis vehicles. To be useful it needs an amplifier and a recording device to capture the signals.
[JTAdams] used a standard amplifier design for an LT1677 op-amp, fed the signal to an MCP3008 A/D converter, and read the output using a Raspberry Pi. A Python script records the data to a CSV file for processing. The Pi worked well because the entire setup needs to be portable to take into the field. Another Python script plots the data which is made available from a web page. A neat simple way of presenting the raw data. [JTAdams] promises more information in the future on post-processing the data. You don’t need a geophone to detect seismic waves if you build your own, but a real ‘phone will be more rugged.
Oh, what’s a vibroseis? It’s a truck with a big flat plate underneath it. The plate is hydraulically lowered to the ground until the weight of the truck is on it. The truck then causes the plate to vibrate, usually sweeping from around 10 hz to 100 hz. This infrasound pass through the ground until it is reflected back by underlying rock layers. A long string of geophones, think 1,000s of feet, detects the waves, which are recorded. In practice, many trucks are used to generate a synchronized signal of sufficient strength. Or, you can set off an explosion which is the technique used in water. Typically the information is used for oil and gas exploration. A video of one of the trucks in action after the break.
Continue reading “Listening To The Sounds Of The Earth”
In the cold and mysterious wilderness of Norway, it pays to be ready for anything–especially heavy-walking trolls. The team at [nullohm] decided to prepare thoroughly for their trek into the woods to witness the Leonids meteor shower by putting together an Arduino-based “troll detector”.
The device is based on the superstition of hammering a steel spike into a tree to keep trolls away from camp. This goes one step further by including an accelerometer and LED indicators so that you can tell exactly what type of troll is just about to feast upon your tender human flesh.
When the detector is installed into a nearby tree, it takes an average seismic measurement and then looks for telltale footfalls. Even if you’re not concerned with perpetuating superstitions, you might find a use for the source code for simple seismic activity monitoring at home to supplement your miniature seismic reflector.
Today we stumbled upon [jimthree’s] Seismic Reflector while looking at projects that employ the Processing language we mentioned a few days ago. Utilizing a Boarduino and some vibration motors from a game controller, the Seismic Reflector does just as its name implies – rattles itself around whenever there is an earthquake. While this does seem a bit silly at first, we were fascinated to learn there have been 165 earthquakes just in the past week and almost no news reports, suddenly this device got a lot more interesting!