Abstract:We describe a new rotational accelerometer exhibiting excellent rotational acceleration sensitivity of 2-3 X 10(-9) rad s(-2)/root Hz for frequencies below 2 Hz and increasing as the square of frequency for frequencies higher than 2 Hz. The sensitivity to horizontal linear accelerations and static tilts is 60 dB less than its rotational sensitivity. The accelerometer has been used to characterize the seismic ground tilt spectrum. Measurements of the performance of the device and of the seismic rotational spect… Show more
“…We report here the successful extension of this to the detection of teleseismic waves (of period • 18-22 seconds) in two more advanced square HeNe ring lasers C-II and GO now at Cashmere. As we show, the noise floor is significantly below that for reported rotational accelerometers [Luiten et al, 1997]. The increase in sensitivity over our earlier work is associated with better engineering (for C-II) or with greater size (for GO); C-II has a monolithic construction in a solid piece of Zerodur (-0.65 tonne), a beam area of 1 m 2, and a quality factor 6 x 10 xa [Stedman, 1997] Other major improvements were important in securing the present results.…”
Abstract.Horizontal and vertical rotational components of teleseismic surface and body waves are detected by large ring laser gyroscopes. This is illustrated with records from magnitudes 7.0 and 7.3 events at distances of 31 deg. and 42.6 deg. respectively. Phase comparisons with synchronous linear seismometer records confirm the gyroscopic coupling.
“…We report here the successful extension of this to the detection of teleseismic waves (of period • 18-22 seconds) in two more advanced square HeNe ring lasers C-II and GO now at Cashmere. As we show, the noise floor is significantly below that for reported rotational accelerometers [Luiten et al, 1997]. The increase in sensitivity over our earlier work is associated with better engineering (for C-II) or with greater size (for GO); C-II has a monolithic construction in a solid piece of Zerodur (-0.65 tonne), a beam area of 1 m 2, and a quality factor 6 x 10 xa [Stedman, 1997] Other major improvements were important in securing the present results.…”
Abstract.Horizontal and vertical rotational components of teleseismic surface and body waves are detected by large ring laser gyroscopes. This is illustrated with records from magnitudes 7.0 and 7.3 events at distances of 31 deg. and 42.6 deg. respectively. Phase comparisons with synchronous linear seismometer records confirm the gyroscopic coupling.
“…3.10. Development of at least three generations of mechanical tiltmeters ended in disappointing performance [35,36], thousands of times the level that could be extrapolated from higher frequency behavior, growing at least with 1/f at the low frequency side. Additionally, it is well known that high precision seismometers need to settle for a "thermalization" time of many hours, which is much longer than the thermalization time constants that one could expect from the heath capacitance and conductivity of their structure.…”
Section: Observational Behaviour and Resultsmentioning
“…Araya et al [12] used DC-2 kHz sensitive seismometer with a sensitivity of 3 × 10 −11 m Hz −1/2 at 1 Hz using a laser interferometer to measure seismic noise acceleration. The VIGRO GW group [13] used a rotational accelerometer with a sensitivity of 2-3 × 10 −9 rad s −2 Hz −1/2 for frequencies below 2 Hz to measure the seismic ground tilt spectrum. The Australian GW group measured twodimensional seismic tilt spectra in their basement laboratory using a double-flexure two-axis tilt sensor with an optical walkoff sensor [14].…”
A laser interferometer combined with a reference mirror suspended on a long-period folded
pendulum is presented to measure the low-frequency horizontal seismic spectrum. One of
the reflecting mirrors is driven by a piezoelectric transducer to track another
mirror. The experimental results show that the horizontal seismic motion is about
10−9 m Hz−1/2
at 1 Hz in our laboratory.
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