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Akito ARAYA (Earthquake Reseach Inst., Univ. of Tokyo, Japan). Broadband observation …. requires low-frequency sensitivity Advantages of Laser Interferometers: ・ high resolution owing to short wavelength of light
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(Earthquake Reseach Inst., Univ. of Tokyo, Japan)
Broadband observation …. requires low-frequency sensitivity
Advantages of Laser Interferometers:
・high resolution owing to short wavelength of light
・low drift using frequency-stabilized laser
・in-situ calibration with reference to wavelength of light
・free from EM noise or heating based on optical sensing
・operation at high-temperature (deep underground)
Laser-interferometer application to broadband observations
・Self calibration (with reference to the laser wavelength)
・Laser-diode as a light source (l=850nm, 5mW)
・Long-period pendulum (f0=7s with a 10-cm mass)
Laser diode as a light source
Prototype laser seismometer
phase delay < 0.2deg.
and both results were agreed well.
----- ~1% as compared with an STS-2 seismometer
----- well below the Low Noise Model (50mHz ~ 100Hz)
estimated from two identical laser seismometers
Comparison with an STS-2 seismometer
(measured at Black Forest Obs.)
---- thermal and
Accelerometer and an air-tight case
No electronic components are installed in the accelerometer
Earth tides （10-7～10-6rad）
Seiche （～10-8rad） occurred in Uraga Channel (entrance of Tokyo Bay)
Turkey earthquake （17 Aug. 1999）
Initial motion -- （～10-8rad）
Maximum amplitude -- （～10-5rad）
Rapid response than that of water-tube tiltmeters.
・Iodine-stabilized Nd:YAG laser (l =532nm, dn/n=2×10-13)
・100-m baseline, 1000-m underground (in Kamioka Mine)
L-shaped 100-m tunnel for
laser strainmeters and
a gravitational-wave detector
Optics in vacuum
Tokachi earthquake (M=8.0)
with predicted one
Laser interferometer … promising method for
・opening up a new window (deep borehole, ocean floor, etc.)
optical-fiber-linked borehole seismometer, tiltmeter, and strainmeter
long-baseline strainmeter with a highly-stabilized laser