pure and applied geophysics

, Volume 101, Issue 1, pp 102–154 | Cite as

Lateral inhomogeneity in the crust and upper mantle fromP-wave amplitudes

  • R. James Brown
Article

Summary

Azimuths and angles of incidence have been calculated from short-periodP-wave amplitude components of 197 events recorded at Umeå, Sweden, near the center of Pleistocene glaciation in Fennoscandia. Anomalies in both sets of data indicate significant departure from a spherically symmetricP-velocity structure. A model incorporating five parameters-strike and dip of equivelocity planes, velocity at the Earth's surface, and at the top and bottom of the heterogeneous zone-is assumed and the parameters are optimized by a computer search. Results, both from the two independent sets of data-incidence-angles and azimuths-as well as from a combined setdirection consines-are mutually consistent and indicate rising equivelocity surfaces, or laterally increasingP velocity, to the ENE in the upper 100 or 200 km of the Earth in the neighbourhood of Umeå. An added refinement, consistent with the results, is an asthenosphere layer pinching out to the ENE, i.e. towards the point of present-day maximum uplift. A surfaceP-wave velocity of about 5.9 km/sec is indicated by the data.

Keywords

Azimuth Pleistocene Asthenosphere Computer Search Pleistocene Glaciation 

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Copyright information

© Birkhäuser Verlag 1972

Authors and Affiliations

  • R. James Brown
    • 1
  1. 1.Seismological InstituteUppsala 1Sweden

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