A Pilot Vertical Seismic Profiling Experiment in the Cajon Pass Deep Scientific Drillhole

The Cajon Pass Deep Scientific Drillhole (see Henyey et al., this volume) is expected to provide one of the first opportunities for a comprehensive study of the crystalline crust using the vertical seismic profiling (VSP) technique. The hole is being drilled to a depth of 5 km through a diverse suite of basement rocks adjacent to the San Andreas fault in southern California. Major low-angle structures of regional importance related to the fault and nearby Transverse Ranges uplift (Fig. 1) are inferred to exist in the Cajon Pass area (e.g. Weldon 1986). Numerous fracture zones (faults?) and petrologic discontinuities have already been intersected in the first 2 km of hole.