Continuous monitoring of propagation velocity of seismic wave using ACROSS

Ikuta, Ryoya

doi:10.1029/2001gl013974

Cited by 57 publications

(78 citation statements)

References 11 publications

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“…Given a 1-week stacking, the signal generated by the ACROSS vibrator can be detected at seismic stations more than 100 km from the source Yoshida et al, 2004). The vibrator used in this study can produce a maximum force of 2×10 5 N, but one can barely feel the vibration even at a distance of 10 m. Ikuta et al (2002) monitored temporal variations in travel time for 15 months using a surface-deployed ACROSS source and seismometers at depths of 800 m and 1700 m in boreholes along the Nojima fault zone, which was the fault zone that ruptured during the 1995 Hyogo-ken Nanbu (Kobe) earthquake. The authors were able to measure temporal variation in the travel time of direct waves over a long period with high accuracy.…”

Section: Introductionmentioning

confidence: 99%

Continuous observation of seismic wave velocity and apparent velocity using a precise seismic array and ACROSS seismic source

Saiga

Yamaoka

Kunitomo³

et al. 2006

Earth Planet Sp

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We report the results of continuous monitoring-using a seismometer array-of the travel time of seismic waves generated by an ACROSS artificial seismic source. The seismometer array, which was deployed in a surface vault located 2.4 km from the source, recorded both direct P-and S-waves and refracted P-and Swaves that traveled along a velocity boundary between the granite basement and overlying sedimentary rocks. We analyzed temporal variation in differential travel time and apparent velocity for these phases for a period of 1 month and found significant temporal variation in the differential travel time. Most of the variation can be attributed to changes in environmental conditions, such as atmospheric temperature and rainfall. Variation is even observed in the seismogram that is located 50 m from the vibration source, although much smaller variation is observed in the vibration of the foundation to which the source is attached. The spectral study revealed that the effects of temperature and rainfall depend strongly on the frequency range used by ACROSS and that a large variation occurs in the 15-to 20-Hz range, especially between 17 and 20 Hz. The environmental effect on the temporal variation is comparable to the record of refracted S waves and that of a distance of 50 m, whereas a larger variation was observed in the direct S wave. This result shows that the signal is affected by the environmental change near the vibration source. The environmental effect can be drastically reduced when the signal from the 15-to 20-Hz range is eliminated in the analysis.

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Section: Introductionmentioning

confidence: 99%

Continuous observation of seismic wave velocity and apparent velocity using a precise seismic array and ACROSS seismic source

Saiga

Yamaoka

Kunitomo³

et al. 2006

Earth Planet Sp

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“…Resolution of temporal variation of the ACROSS signal depends on the SNR after the data stacking (Ikuta et al 2002). We have estimated the noise level in and around Sakurajima Volcano using the same seismic data of the explosion experiment as used in the previous section.…”

Section: Noise Levelmentioning

confidence: 99%

Active monitoring at an active volcano: amplitude-distance dependence of ACROSS at Sakurajima Volcano, Japan

et al. 2014

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First testing of volcanic activity monitoring with a system of continuously operatable seismic sources, named ACROSS, was started at Sakurajima Volcano, Japan. Two vibrators were deployed on the northwestern flank of the volcano, with a distance of 3.6 km from the main crater. We successfully completed the testing of continuous operation from 12 June to 18 September 2012, with a single frequency at 10.01 Hz and frequency modulation from 10 to 15 Hz. The signal was detected even at a station that is 28 km from the source, establishing the amplitude decay relation as a function of distance in the region in and around Sakurajima Volcano. We compare the observed amplitude decay with the prediction that was made before the deployment as a feasible study. In the prediction, we used the existing datasets by an explosion experiment in Sakurajima and the distance-dependent amplitude decay model that was established for the ACROSS source in the Tokai region. The predicted amplitude in Sakurajima is systematically smaller than that actually observed, but the dependence on distance is consistent with the observation. On the basis of the comparison of the noise level in Sakurajima Volcano, only 1-day stacking of data is necessary to reduce the noise to the level that is comparable to the signal level at the stations in the island.

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“…This bearing was developed to support large load rotors such as large eccentric rotors similar to those used in vibration exciters. These exciters were developed to detect subtle changes in the physical state of the Earth's structure using a precise and continuous sinusoidal signal (Kumazawa, et al, 2000), (Ikuta, et al, 2002), (Yamaoka, et al, 2001). Because these devices are set underground, the use of an asymmetric supply type bearing is suitable for ease of maintenance.…”

Section: Introductionmentioning

confidence: 99%

Experimental verification of externally pressurized gas journal bearings with asymmetric gas supply (Supply gas pressure control operation using a small size test rig)

Ise

Imanishi

Asami

et al. 2014

JAMDSM

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Experimental verification of externally pressurized gas journal bearings with asymmetric gas supply (Supply gas pressure control operation using a small size test rig) 2Ise, Imanishi, Asami, Tokumiya, Takada, Kimura and Yamaguchi, Journal of Advanced Mechanical Design, Systems, and Manufact, Vol.8, No.3 (2014) © 2014 The Japan Society of Mechanical Engineers [DOI: 10.1299/jamdsm.2014jamdsm0029] Fig. 1 Configuration of an X-ray CT gantry being more useful in terms of support of the load compared with the previously developed bearings (Okano, et al., 2006), (Ise, et al., 2007a), (Ise, et al., 2010), (Ise, et al., 2007b).We propose that this type of bearing is applicable for use in an X-ray computed tomography (hereafter called as X-ray CT) scanner gantry (Tokumiya, et al., 2013). The rotary drum of the gantry has electrical units to computed tomography scanning, as shown in Fig.1. The drum is supported by rolling contact bearing. The dynamic unbalance is roughly canceled by the arrangement of these devices. The rotary drum inner diameter is 800 or 1,000 mm and the rotating speed is 100 or 220 rpm. In present devices, rolling contact bearings are used to support the rotor. The maximum circumferential speed exceeds 11.5 m/s in present conditions. Rotation produces a somewhat unbalanced centrifugal force since the rotary drum has a small eccentricity although the unbalance is cancelled; therefore, the force due to residual unbalance with the drum mass gives to the bearings as the load. For these reasons, a large torque is required in the operation. A greater rotational speed is presently demanded of the gantry because realization of high speed rotation will result in higher precision scanning. However, a higher rotational speed results in a shorter bearing lifetime and an increase of noise, which tends to create higher patient anxiety. Radiation exposure of the patient also can be reduced by this mechanism because examination time decreases by high speed rotation. The use of the proposed gas bearings can potentially solve these problems.The final purpose is application of this bearing for the X-ray CT gantry. For this purpose, verification of the proposed bearing mechanism under the supply gas pressure control condition is first necessary. This report presents rotational tests of the proposed hydrostatic gas journal bearings with asymmetric gas supply using a small sized preliminary test rig to verify the effectiveness of the proposed mechanism. Ise, Imanishi, Asami, Tokumiya, Takada, Kimura and Yamaguchi, Journal of Advanced Mechanical Design, Systems, and Manufact, Vol.8, No.3 (2014) Working mechanism of the proposed bearingExperimental verification of the capacity of externally pressurized gas journal bearings with asymmetric gas supply (called AGS bearings hereafter) to support large load rotors was conducted. The working mechanism and the characteristics of the AGS bearing were examined by comparison with the conventional type of externally pressurized gas journal bearing. A schematic of the proposed AG...

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Continuous monitoring of propagation velocity of seismic wave using ACROSS

Cited by 57 publications

References 11 publications

Continuous observation of seismic wave velocity and apparent velocity using a precise seismic array and ACROSS seismic source

Continuous observation of seismic wave velocity and apparent velocity using a precise seismic array and ACROSS seismic source

Active monitoring at an active volcano: amplitude-distance dependence of ACROSS at Sakurajima Volcano, Japan

Experimental verification of externally pressurized gas journal bearings with asymmetric gas supply (Supply gas pressure control operation using a small size test rig)

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