Dispersion analysis of crack waves for a low-velocity-layer model of an artificial subsurface fracture.

This paper investigates a low-velocity-layer (LVL) model for an artificial subsurface fracture examining dispersions of crack waves. Subsurface fractures are important in extracting geothermal energy. The crack waves are seismic modes propagating along the fracture. The LVL represents a zone in which many small fractures are distributed around a main single fracture. The crack waves were measured at an artificial subsurface fracture at a depth of about 370 m in the Tohoku University Higashi-Hachimantai Hot Dry Rock model field, Japan. The wavelet transform is applied to describe the dispersion of the crack waves. Crack-wave dispersions affected by the pressurization of the subsurface fracture are obtained. The numerical dispersion curves are also calculated in the LVL model using a matrix method. When the aperture of the subsurface fracture increases by the pressurization, the LVL model shows good agreement with the crack-wave dispersion. The LVL model is, however, insufficient for the crack-wave dispersion detected at the beginning of pressurization. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 58–69, 2000 [ABSTRACT FROM AUTHOR]