Quake plot of recent 5.3 earthquake. WISRD’s seismometer on the Caltech Seismic Network was closest to event.
We have installed a seismometer as a node on the California Seismic Network sponsored by Caltech. We are collecting data in real time.
No current research project.
A seismometer is a device that measures seismic activity, such as earthquakes and volcanic activity. The modern seismometer is derivative of the seismoscope, which originated in China in 132 CE.
Figure 1: Model of a seismoscope in the Chabot Space and Science Center
The seismoscope used metal balls held in clamps and put in the center of town. When the earth shook, a pendulum would hit a lever that would open the clamp nearest to the seismologic event. This would indicate that an Earthquake was about to happen and which direction the event was happening. The design was refined and the ornate dragons, toads, pot, lever and clamps were removed. Most modern seismometers are a simple stationary pendulum with a piece of graphite attached at the end. With these designs when an seismologic event occurred, the pendulum would move the graphite up and down. This allows for the measurement of the magnitude of the event. Magnitude is the measure of the amount of energy released during an earthquake. The energy released is put into context by the Richter scale. The Richter scale is logarithmic, with a base of 10. The amplitude of an earthquake that scores 3.0 is about 10 times the amplitude of one that scores 2.0. The energy that is released increases by a factor of 32.
Figure 2: Diagram of a Pendulum Seismometer
This is how seismologic activity has been measured since the 1930s. However, since the invention of optical circuitry a far more sensitive seismometer has become available to the public, the Optical Seismometer. This seismometer is still comprised of a pendulum, but instead of graphite it uses a laser traveling through a fiber optics cable. The light from the laser, when an earthquake isn’t occurring, will be shining upon a photodiode. When the light moves away from the photodiode a small current will be able to pass through a circuit. This current can be measured. If an earthquake happens, then the light will swing back and forth over the photodiode intermittently allowing for a current pass through it. This current is very small and difficult to detect by most data loggers. To increase the sensitivity, the current will pass through an operational amplifier to increase the voltage. The frequency of each time a current is allowed to pass through can be used to determine the magnitude of an earthquake.
Figure 3: Line diagram of the circuitry involved in an optical seismometer
This optical seismometer is a helpful, and easy to build, tool that could give an more time to prepare for an earthquake. As someone whose family survived the Christchurch Earthquake of 2008, I know more time can save lives.