08:30 〜 08:45
[G04-3-01] Long-baseline laser strainmeter constructed at the underground KAGRA site in Kamioka as a new tool for monitoring crustal dynamics
Ground motion and its deformation have been monitored by various instruments with very wide ranges in amplitudes and timescales. Strainmeters measure deformation of the ground by sensing distance between two separated points, and cover crustal observation of small strain changes at low frequencies. However, the strainmeters tend to suffer from local disturbances and instabilities of reference for the distance measurement. Long-baserline laser strainmeters that measure distance of separation of 10-1000m based on highly stable optical wavelength of laser can avoid some of the problems.
A 100-m laser strainmeter [1] at an underground site in Kamioka, Gifu Prefecture, Japan, showed reliable detection of coseismic crustal deformation associated with remote earthquakes and provided estimation of seismic moment based on far-field geodetic observation [2]. It also showed the baseline (100m) was not enough for long-term strain observation because groundwater pressure of seasonal timescale affected the ground strain.
In 2016, a new laser strainmeter with a 1.5-km baseline was constructed at an underground site along KAGRA gravitational wave detector [3] in Kamioka and started test observation. With the long baseline, the strainmeter clearly detected earth tides which almost agreed with theoretical calculations. We discuss its detectability for long-term strain changes in comparison to the 100-m laser strainmeter and prospect for monitoring crustal dynamics using the long-baseline strainmeter.
[1] S. Takemoto et al., A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan, Journal of Geodynamics, 38, 477-488, 2004.
[2] A. Araya et al, Analyses of far-field coseismic crustal deformation observed by a new laser distance measurement system, Geophys. J. Int., 181, 127-140, 2010.
[3] Y. Aso et al, Interferometer design of the KAGRA gravitational wave detector, Phys. Rev. D, 88, 043007, 2013.
A 100-m laser strainmeter [1] at an underground site in Kamioka, Gifu Prefecture, Japan, showed reliable detection of coseismic crustal deformation associated with remote earthquakes and provided estimation of seismic moment based on far-field geodetic observation [2]. It also showed the baseline (100m) was not enough for long-term strain observation because groundwater pressure of seasonal timescale affected the ground strain.
In 2016, a new laser strainmeter with a 1.5-km baseline was constructed at an underground site along KAGRA gravitational wave detector [3] in Kamioka and started test observation. With the long baseline, the strainmeter clearly detected earth tides which almost agreed with theoretical calculations. We discuss its detectability for long-term strain changes in comparison to the 100-m laser strainmeter and prospect for monitoring crustal dynamics using the long-baseline strainmeter.
[1] S. Takemoto et al., A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan, Journal of Geodynamics, 38, 477-488, 2004.
[2] A. Araya et al, Analyses of far-field coseismic crustal deformation observed by a new laser distance measurement system, Geophys. J. Int., 181, 127-140, 2010.
[3] Y. Aso et al, Interferometer design of the KAGRA gravitational wave detector, Phys. Rev. D, 88, 043007, 2013.