We report on the first joint search for gravitational waves by the TAMA and LIGO collaborations. We looked for millisecond-duration unmodeled gravitational-wave bursts in 473 hr of coincident data collected during early 2003. No candidate signals were found. We set an upper limit of 0.12 events per day on the rate of detectable gravitational-wave bursts, at 90% confidence level. (2005) 122004-3 simulations, we estimate that our detector network was sensitive to bursts with root-sum-square strain amplitude above approximately 1-3 10 ÿ19 Hz ÿ1=2 in the frequency band 700-2000 Hz. We describe the details of this collaborative search, with particular emphasis on its advantages and disadvantages compared to searches by LIGO and TAMA separately using the same data. Benefits include a lower background and longer observation time, at some cost in sensitivity and bandwidth. We also demonstrate techniques for performing coincidence searches with a heterogeneous network of detectors with different noise spectra and orientations. These techniques include using coordinated software signal injections to estimate the network sensitivity, and tuning the analysis to maximize the sensitivity and the livetime, subject to constraints on the background.
We analyzed continuous GPS data from more than 20 sites in Asia, Australia and islands in Indian Ocean in order to detect crustal deformations associated with the Sumatra-Andaman earthquake of December 26, 2004. Coseismic steps can be recognized at sites about 3,000 km away from the epicenter such as Kunming in south China, Quezon in Philippines, and Diego Garcia Island in central Indian Ocean. The largest displacement of about 26 cm is found at Phuket in Thailand about 600 km away from the epicenter, about twice as large as that at Sampari, the nearest site in northern Sumatra. These observations suggest that as large slip as 14 m occurred beneath the Nicobar Islands. Large postseismic displacements are observed at Phuket and Sampari after the mainshock, but the former is three times larger than the latter. This suggests that the spatial distribution of afterslip is different from the coseismic slip distribution. The temporal variation of postseismic displacements can be explained by a logarithmic function derived from rate-state dependent friction law with short characteristic time. The area where coseismic displacements from the Nias earthquake of March 28, 2005 are detected is much smaller than that from the December mainshock, but displacement at Sampari is larger than that during the mainshock. These displacements suggest less than 4 m slip on a shallow dipping thrust fault and resultant moment release is smaller than that estimated from seismological data. Finally, total moment released by afterslip amounts to 3.83 × 10 22 Nm which is equivalent to Mw 8.99 for about five months, including the afterslip for the Nias earthquake.
The CLIO project involves the Cryogenic Laser Interferometer Observatory (CLIO) detector complex for gravitational wave detection and the Kamioka Laser Interferometric Strainmeter for the acquisition of geophysical data. CLIO has been constructed to demonstrate the feasibility of a future project, the Large-scale Cryogenic Gravitational wave Telescope (LCGT). It will utilize the low seismic and stable environment of the Kamioka mine as well as sapphire mirrors and suspension fibres at low temperature to reduce thermal noise. We designed CLIO to have a noise level limited by the thermal noise of sapphire mirrors and sapphire suspension fibres, which vary from 3 × 10−19 m Hz−1/2 at 300 K to 2 × 10−20 m Hz−1/2 at 20 K around 100 Hz. The strainmeter has already succeeded in monitoring the Earth's tidal motion with a strain sensitivity of 2 × 10−12. The seismic noise veto between these same-scale interferometers is expected to provide an effective means of data selection for the gravitational wave signal analysis, and the ground motion data obtained by the strainmeter will help to maintain the stable operation of CLIO.
Construction of CLIO (cryogenic laser interferometer observatory) with 100 m baseline length has begun in the Kamioka mine. The tunnel for CLIO has been dug and infrastructure work is now in progress. CLIO is the final step to LCGT (large scale cryogenic gravitational wave telescope) and the first practical construction of a cryogenic interferometer in the world. The objective of CLIO is to demonstrate two of three features of LCGT, which are to utilize the quietness and stable environment of the underground site and to adopt cryogenic sapphire mirrors for thermal noise reduction. Also, it is a joint project by gravitational wave and geophysics researchers.CLIO has a locked Fabry–Perot configuration equipped with ring mode cleaners and cryocoolers to cool the sapphire mirrors to 20 K. The noise level of CLIO is designed to trace the thermoelastic noise of sapphire mirrors which varies from 10−18 m Hz−1/2 at 300 K to 10−19 m Hz−1/2 at 20 K around 100 Hz.A 7 m single-arm cryogenic test facility has been built at ICRR (Institute for Cosmic Ray Research), while the 20 m room temperature interferometer is in operation at Kamioka. Technical knowledge developed by these prototypes will be leveraged to realize CLIO.
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