| 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. |
| Genre: | USGS Unnumbered Series |
| ProdID: | 70040819 |
| Citation Author: | Pakiser, L. C. |
| Citation Contributing Office: | Earthquake Science Center |
| Citation Datum: | |
| Citation Day: | |
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| Citation End Page: | |
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| Citation Language: | English |
| Citation Larger Work Title: | |
| Citation LatN: | 71.833333 |
| Citation LatS: | 13.233333 |
| Citation LonE: | -64.566667 |
| Citation LonW: | 144.616667 |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 28 |
| Citation Online Only Flag: | Y |
| Citation Phsyical Description: | iv, 24 p. |
| Citation Projection: | |
| Citation Public Comments: | In cooperation with the Defense Advanced Research Projects Agency |
| Citation Publisher: | U.S. Geological Survey |
| Citation Series: | Crustal Studies Technical Letter |
| Citation Series Code: | |
| Citation Series Number: | 20 |
| Citation Search Results Text: | Continental crust; 1964; USGS Unnumbered Series; 20; Pakiser, L. C. |
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| Citation Volume: | |
| Citation Year: | 1964 |
| Type: | citation/reference |
| Text: | Continental crust; 1964; USGS Unnumbered Series; 20; Pakiser, L. C. |
| URL (INDEX PAGE): | http://pubs.usgs.gov/misc/tl/0020/ |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/usgs_thumb.jpg |
| URL (DOCUMENT): | http://pubs.usgs.gov/misc/tl/0020/tl0020.pdf |
| Date Other: | Sun, 1 Jan 2012 00:00 -0600 |
| Publisher: | U.S. Geological Survey |
