Direction Of Maximum Velocity Research Articles

A Measurement of Seismic Anistropy in the Northeast Pacific

A seismic refraction experiment was conducted in the Pacific Ocean basin, off the coast of British Columbia, Canada. The purpose of these measurements was to obtain an estimate of the anisotropy of the mantle P-wave velocity in the area and to relate this parameter to the direction of sea floor spreading. The results show that the crustal structure is similar to that measured elsewhere in the Pacific basin. Significant anisotropy of the mantle rocks is observed; the direction in which the maximum velocity occurs being 107° and the change of velocity, about 8% of the mean value, 8.07 km/s. The direction of maximum velocity does not coincide exactly with the direction of sea floor spreading, 090°, inferred from magnetic lineations.

Velocity Anisotropy of Upper Mantle: ABSTRACT

End_Page 469------------------------------During the summer of 1966 a joint marine refraction survey was conducted across the Hawaiian arch by the Scripps Institution of Oceanography, the University of Hawaii, Oregon State University, and the University of Wisconsin. Conventional and unique types of refraction profiles were shot to study the directional dependence of velocity or velocity anisotropy of the mantle and the depth configuration of the Mohorovicic discontinuity. A two-dimensional delay time function method was used to study (1) the anisotropy and (2) the delay-time surface. The upper mantle was found to display compressional velocity anisotropy amounting to about 0.6 km/sec difference between the maximum and minimum velocities with the direction of maximum velocity being east-west. The delay time surface suggests t at, as expected from earlier work, the mantle is generally shallow along the crest of the arch. The shallowest region occurs near the southeast end of the arch, where it intersects the Molokai fracture zone. The mantle deepens southwest of the crest of the arch as the Hawaiian deep is approached. End_of_Article - Last_Page 470------------