Correlation of paleotectonic fracture and microfracture orientations in cores with seismic anisotropy at Cajon Pass Drill Hole, southern California

Fractures and microfractures in oriented cores from the Cajon Pass drill hole, southern California, have strong preferred orientations. There are two major sets of extensional fractures and microfractures that have northwest and northeast strikes and vertical dips. Relative and absolute densities of both sets vary greatly within a single core. The regional tectonic history implies that these fractures and microfractures probably formed before late Miocene‐Pliocene. Vertical seismic profiling experiments in the drill hole show shear wave splitting with polarization directions parallel to the fracture and microfracture orientations. The measured seismic anisotropy is due to these inherited deformation fabrics and does not appear to be caused by the current local stress field.