<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Walter D. Mooney</dc:contributor>
  <dc:creator>G.S. Chulick</dc:creator>
  <dc:date>2002</dc:date>
  <dc:description>&lt;div class="article-section-wrapper js-article-section "&gt;&lt;p&gt;We present a new set of contour maps of the seismic structure of North America and the surrounding ocean basins. These maps include the crustal thickness, whole-crustal average&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-wave and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave velocity, and seismic velocity of the uppermost mantle, that is,&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;Pn&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;Sn&lt;/i&gt;. We found the following: (1) The average thickness of the crust under North America is 36.7 km (standard deviation [s.d.] ±8.4 km), which is 2.5 km thinner than the world average of 39.2 km (s.d. ± 8.5) for continental crust; (2) Histograms of whole-crustal&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;- and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave velocities for the North American crust are bimodal, with the lower peak occurring for crust without a high-velocity (6.9–7.3 km/sec) lower crustal layer; (3) Regions with anomalously high average crustal&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-wave velocities correlate with Precambrian and Paleozoic orogens; low average crustal velocities are correlated with modern extensional regimes; (4) The average&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;Pn&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;velocity beneath North America is 8.03 km/sec (s.d. ± 0.19 km/sec); (5) the well-known thin crust beneath the western United States extends into north-west Canada; (6) the average&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-wave velocity of layer 3 of oceanic crust is 6.61 km/sec (s.d. ± 0.47 km/sec). However, the average crustal&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-wave velocity under the eastern Pacific seafloor is higher than the western Atlantic seafloor due to the thicker sediment layer on the older Atlantic seafloor.&lt;/p&gt;&lt;/div&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1785/0120010188</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Geological Society of America</dc:publisher>
  <dc:title>Seismic structure of the crust and uppermost mantle of North America and adjacent oceanic basins: A synthesis</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>