Fracture related reflectors in basement rock from vertical seismic profiling at Cajon Pass



Multi-azimuth VSP data acquired between 500 and 2000 meters deep in crystalline rock penetrated by the Cajon Pass deep scientific borehole show several reflectors intersecting the hole. The reflectors correlate with VSP amplitude data, drilling and cutting logs, and various geophysical logs. Most appear to be related to fracture zones or lithologic transitions accompaanied by fracturing, mineral alteration and fluid circulation. Amplitude systematics from two azimuthally different offsets are consistent with the presence of a high angle fault in the neighborhood of the well.