This paper describes the results of seismic reflection surveys conducted using a horizontally polarized shear (SH) wave-type vibrator. In the study, post-migrated CMP profiles of seismic reflection processing were produced to characterize subsurface structures across both the Asahiyama flexure and the Kozu-Matsuda fault. The throw of the top reflector enabled estimation of the cumulative vertical offset in the bedrock across the fault, and refraction tomography processing also revealed the SH wave velocity structure across it. The velocity structure in the subsurface around the fault decreased to 300 or 500 m/s. This was considered to be the result of unfavorable geological conditions with a low shear modulus. Against this background, SH-wave seismic reflection surveys are strongly expected to be very useful for acquiring images of bedrock across active faults, approximating the depth of bedrock, and identifying dataset signal anomalies that may indicate unfavorable geological conditions. These benefits are owed to the lower speed and shorter wavelength of SH waves. |