期刊
BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA
卷 92, 期 6, 页码 2478-2492出版社
SEISMOLOGICAL SOC AMER
DOI: 10.1785/0120010188
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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 P-wave and S-wave velocity, and seismic velocity of the uppermost mantle, that is, Pn and Sn. We found the following: (1) The average thickness of the crust under North America is 36.7 kin (standard deviation [s.d.] +/- 8.4 km), which is 2.5 kin thinner than the world average of 39.2 km (s.d. +/- 8.5) for continental crust; (2) Histograms of whole-crustal P- and S-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 P-wave velocities correlate with Precambrian and Paleozoic orogens; low average crustal velocities are correlated with modem extensional regimes; (4) The average Pn 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 northwest Canada; (6) the average P-wave velocity of layer 3 of oceanic crust is 6.61 km/sec (s.d. +/- 0.47 km/sec). However, the average crustal P-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.
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