Development of a Broadband Optical Seismometer: Phase 2

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A great deal of our knowledge of the Earth's interior comes from seismology: the analysis of elastic waves propagating through the Earth. Seismometers measure these waves, and the science of building more and more sensitive seismometers extends back for many years. Almost all seismometers consist of a mass suspended by a spring. Usually an electronic circuit senses the displacement of the mass (with respect to the seismometer's frame) when a seismic wave produces a local vibration. Under continuing funding from the National Science Foundation, we are developing a new seismometer which uses optics instead of electronics to sense mass motion. New signal-processing electronics allow us to analyze laser light reflected from the seismometer mass and detect displacements as small as a trillionth of a meter. A variety of advantages are afforded from this new technique, including a high dynamic range and wide bandwidth, a calibration based on the wavelength of laser light, a connection to the sensor via fiber optic cables rather than electrical ones, and elimination of electronics in the sensor package. Our research over the next two years will include further noise-reduction efforts and independently monitored tests of our new seismometer at seismic observatories other than our own.