October 10, 2006

Prototype Fiber Optic Seismometer

Modern seismometers throughout the world, including those on HPWREN, rely on electronic displacement transducers to sense motions of an inertial mass, whenever the earth's surface moves. New advances in optical fiber technology are providing an alternative to this type of modern observatory grade seismometer.

SIFO Control Center
Seismometer Incorporating Fiber Optics (SIFO) Control Center. This computer rack allows Scripps Institution of Oceanography scientists to control every aspect of the prototype fiber optic seismometer. The computer screen towards the bottom of the photo is remotely viewed from UCSD via the HPWREN network.

Scientists at Scripps Institution of Oceanography, have developed an optical fringe resolver to replace the electronic displacement transducers found in current seismometers. The optical fringe resolver uses a 633 nm polarization stabilized laser and a Michelson interferometer to detect minute movements of the earth's surface. The use of fiber optics has many benefits including immunity to electronic noise, the elimination of heat sources (a significant problem in modern seismometry) and the elimination of electrical connections between the seismometer and outside world (an important consideration in environments with lightning).

PFO vault
These photos show the underground vault at the Piñon Flats Observatory (near Anza, California), which is connected via HPWREN. The fiber optic seismometer sits on the granite pier (right photo towards the bottom), which is coupled to the earth and isolated from the vault and the wood floor.
PFO vault

The current prototype SIFO (Seismometer Incorporating Fiber Optics) is running in an underground seismic vault at the Piñon Flats Observatory in Anza, California. The seismometer relies on the HPWREN for data transfer and operation.

Prototype Fiber Optic Seismometer
Scientists at Scripps Institution of Oceanography have designed a prototype seismometer which uses lasers and fiber optics to detect small movements within the earth.

Jose Otero
Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography

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