Seismic anisotropy due to preferred mineral orientation observed in shallow crustal rocks in southern Alaska

Laboratory velocity measurements and structural field relations explain the observation of a significant seismic anisotropy within highly foliated rocks in southern Alaska. The orientation of the principal compressive stress indicates that this anisotropy is not related to extensive dilatancy, but can be satisfactorily explained by the foliation of the metasedimentary rocks. Laboratory measurements indicate a significant anisotropy within these rocks even at pressures well above those thought to close microcracks. These observations document that anisotropy related to preferred mineral orientation may be widespread in continental rocks. Thus, pervasive foliation can play a more important role in causing anisotropy than dilatancy, and inferences of principal stress orientations solely from anisotropy may be erroneous.