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Polarization of crack waves along an artificial subsurface fracture
Author(s) -
Nagano Koji,
Sato Kazuhiko,
Niitsuma Hiroaki
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl02051
Subject(s) - shear waves , geology , longitudinal wave , polarization (electrochemistry) , shear (geology) , azimuth , fracture (geology) , wave propagation , seismology , mechanics , optics , physics , geotechnical engineering , petrology , chemistry
We analyze three‐dimensional (3D) particle motions of crack waves which propagate along a fracture to determine fracture orientation. Crack waves were measured at an artificial subsurface fracture at a depth of approximately 370 m in the Higashihachimantai Hot Dry Rock model field in Japan. Dispersion was observed in crack waves. Velocities of crack waves below 100 H z are 100 m/s–150 m/s along this artificial fracture. Therefore, crack waves arrived after compressional wave and shear wave. A coherence matrix is used to analyze the 3D particle motions in the frequency domain. Noise, which is outside of the band of the detector, is excluded in the coherence matrix analysis. We examine the polarization of 3D particle motions of crack waves using Principal Component Analysis. The longest axis of an ellipsoid which approximates the 3D particle motions shows a direction consistent with estimates obtained by core‐sample measurements and tectonic stress measurements. The differences in fracture orientation obtained from the crack‐wave analysis and the core sample analysis are less than 16° in azimuth and less than 20° in dip.