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Continental crust

Crustal Studies Technical Letter 20

In cooperation with the Defense Advanced Research Projects Agency
By:

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Abstract

The structure of the Earth’s crust (the outer shell of the earth above the M-discontinuity) has been intensively studied in many places by use of geophysical methods. The velocity of seismic compressional waves in the crust and in the upper mantle varies from place to place in the conterminous United States. The average crust is thick in the eastern two-thirds of the United States, in which the crustal and upper-mantle velocities tend to be high. The average crust is thinner in the western one-third of the United States, in which these velocities tend to be low. The concept of eastern and western superprovinces can be used to classify these differences. Crustal and upper-mantle densities probably vary directly with compressional-wave velocity, leading to the conclusion that isostasy is accomplished by the variation in densities of crustal and upper-mantle rocks as well as in crustal thickness, and that there is no single, generally valid isostatic model. The nature of the M-discontinuity is still speculative.

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Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Unnumbered Series
Title:
Continental crust
Series title:
Crustal Studies Technical Letter
Series number:
20
Year Published:
1964
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Earthquake Science Center
Description:
iv, 24 p.
Country:
United States
Online Only (Y/N):
Y
Additional Online Files(Y/N):
N