A Comment on the Evidence for a Worldwide Zone of Low Seismic Velocity at Shallow Depths in The Earth's Crust

  1. John G. Heacock
  1. J. H. Healy

Published Online: 15 MAR 2013

DOI: 10.1029/GM014p0035

The Structure and Physical Properties of the Earth's Crust

The Structure and Physical Properties of the Earth's Crust

How to Cite

Healy, J. H. (1971) A Comment on the Evidence for a Worldwide Zone of Low Seismic Velocity at Shallow Depths in The Earth's Crust, in The Structure and Physical Properties of the Earth's Crust (ed J. G. Heacock), American Geophysical Union, Washington D. C.. doi: 10.1029/GM014p0035

Author Information

  1. National Center for Earthquake Research, U.S. Geological Survey, Menlo Park, California 94025

Publication History

  1. Published Online: 15 MAR 2013
  2. Published Print: 1 JAN 1971

ISBN Information

Print ISBN: 9780875900148

Online ISBN: 9781118664049

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Keywords:

  • Earth's crust;
  • Lasa study;
  • Low velocity layer;
  • North America;
  • Seismic velocity

Summary

Seismic data recorded on the North American continent reveal that the properties and thicknesses that are derived from these data must be regarded as statistical numbers which represent the structure of the earth's crust with varying degrees of reliability, depending on the validity of the assumptions. For example, seismic ,vaves traveling between distances of 10 to 20 km from the source almost always exhibit velocities of 6 km/sec. However, in detail, the rocks along this profile may have a wide range of seismic velocities, and it is only in an average sense that we can describe the top of the crust as a layer with a velocity of 6km/sec. The data recorded at the Lasa detection network in Montana are used to illustrate the degree of scatter in seismic properties that can be measured in a limited area and to point out the difficulties this statistical scatter presents to methods of interpretation commonly used to define low-velocity layers within the crust.