Bringing optical technology to the seismograph
Earthquakes remain one of Earth's most potent natural disasters. Europe is home to several seismically active regions including, but not limited to, the Mediterranean. Effective assessment of seismic risk relies on long-term monitoring with accurate instrumentation. Traditional sensors are based on mechanical components that record motion in three dimensions. The Fifth Framework Programme funded the OPTSDET project whose aim was to introduce optical techniques to seismic instrumentation. The Applied Optics Group of the University of Kent at Canterbury (UKC), a partner in the project, created a new breed of sensors based on Michelson interferometry. In order to cover the large range required without sacrificing resolution, UKC developed two complementary accelerometers, one low resolution and one high resolution. The low resolution unit employs optical fibres and mirrors that mimic the mass-spring oscillators in conventional systems. Fibre length and ends are constrained to overcome problems with polarisation, backreflection, etc. Optical fibres also form the heart of the high resolution accelerometer, encompassing a pair of compliant cylinders. The OPTSDET prototypes promise significant improvement in the signal-to-noise ratio and other performance characteristics. UKC was also able to successfully combine multiple sensors to provide tri-axial measurements, which are required to fully characterise earthquakes.
