Description
What makes a seismograph “broadband”? It refers to the range of frequencies that it can detect, which is determined by the design of the sensor. Some sensors can detect very high frequencies but use springs or other elements that are too stiff to detect very slow oscillations. Some sensors are very sensitive to low frequency oscillations but cannot move quickly enough to capture high frequencies. Some sensors use electronics to boost sensitivity in particular frequency ranges, at the expense of increased noise at other frequencies.
In earthquake terms, a short period seismometer is generally one that outputs the same amplitude of signal when shaken at 2Hz or higher, but when shaken slower than 2Hz the output amplitude no longer matches the physical reality. These sensors tend to have a linear amplitude response to 1000Hz+. A medium-period seismometer is one that has a linear amplitude output when shaken at cycles as slow as a 60-second period (0.016Hz), and they tend to lose linearity at 100-200Hz.
A long-period sensor is one that is linear from 120-360 seconds to 50-100Hz, and this tends to be the sensors that are referred to as “broadband” as they can capture the frequencies from most global and local earthquakes, assuming they have a sufficiently low self-noise level across that frequency band. The trade-off is that these sensors tend to be handled carefully and may not be suited to portable applications. Be wary of very cheaper sensors that claim to be able to detect oscillations at 360-second periods – they may only detect high amplitude signals due to high self-noise levels, making them impractical for some research applications.
Talk to our experts on which sensor options would suit your application so that you get the right tool for the job and that you’re not paying for performance that you don’t need. The Gecko seismic data logger is compatible with any seismic sensor on the market, so your choice for data recording and streaming is easy. Available as the low-cost Gecko Compact, the waterproof Gecko Rugged, and variants that integrate sensors, backup batteries and communications systems, we have your data acquisition and streaming needs sorted.
