抄録
This paper investigates a low-velocity-layer (LVL) model for an artificial subsurface fracture examining dispersions of crack-waves. Subsurface fracture is important to extract 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 370m in Tohoku University Higashi-Hachimantai Hot Dry Rock model field, Japan. The Wavelet Transform is applied to describe the dispersion of the crack-waves. I obtain the crack-wave dispersions which are affected by the pressurization of the subsurface fracture. 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 a good agreement with the crack-wave dispersion. The LVL model is, however, insufficient for the crack-wave dispersion detected at the beginning of the pressurization.
