1. Laser-interferometer application to broadband observations 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 ・ 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)

2. Features of the laser-interferometric seismometer ・ Self calibration (with reference to the laser wavelength) Principle Block diagram

3. Features of the laser-interferometric seismometer ・ Laser-diode as a light source (l=850nm, 5mW) ・ Long-period pendulum (f 0 =7s with a 10-cm mass) Prototype laser seismometer Laser diode as a light source

4. Frequency response Features of the laser-interferometric seismometer ・ Wideband feedback (UGF=1kHz, phase delay < 0.2deg. below 100Hz)

5. Two calibration method were applied and both results were agreed well.

6. Comparison with an STS-2 seismometer ・ Accuracy of the self calibration ----- ~1% as compared with an STS-2 seismometer ・ Self-noise level ----- well below the Low Noise Model (50mHz ~ 100Hz) estimated from two identical laser seismometers Self-noise estimation (measured at Black Forest Obs.)

7. Current problems ---- thermal and barometric response

8. Optical-fiber-linked version of a laser seismometer (under development) Accelerometer (vertical) Accelerometer and an air-tight case No electronic components are installed in the accelerometer

9. Optical-fiber-linked borehole tiltmeter

10. A pendulum-type tiltmeter with laser interferometers

11. Test observation in an 80-m-deep borehole at Nokogiriyama observatory

12. Comparison with water-tube tiltmeters Earth tides （ 10 -7 ～ 10 - 6 rad ） Seiche （～ 10 -8 rad ） occurred in Uraga Channel (entrance of Tokyo Bay)

13. Earthquake observation Turkey earthquake （ 17 Aug. 1999 ） Initial motion -- （～ 10 -8 rad ） Maximum amplitude -- （～ 10 - 5 rad ） Rapid response than that of water-tube tiltmeters.

14. Laser strainmeter as a broadband seismometer ・ Iodine-stabilized Nd:YAG laser (l =532nm, dn/n=2×10 -13 ) ・ 100-m baseline, 1000-m underground (in Kamioka Mine)

15. Location of Kamioka Mine --- about 200km northwest of Tokyo

16. Map in the mine (-1000m level) L-shaped 100-m tunnel for laser strainmeters and a gravitational-wave detector Super KAMIOKANDE (neutrino detector)

17. Schematic diagram

18. Iodine-stabilized Nd:YAG laser

19. Optics in vacuum Twin bellows

20. Background noise level

21. Comparison with CMG seismometers

22. Tokachi earthquake (M=8.0) Excited free oscillation

23. Earth tides compared with predicted one

24. Summany Laser interferometer … promising method for ・ opening up a new window (deep borehole, ocean floor, etc.) optical-fiber-linked borehole seismometer, tiltmeter, and strainmeter ・ improving sensitivity long-baseline strainmeter with a highly-stabilized laser