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Seismic structure of the crust and uppermost mantle of South America and surrounding oceanic basins

Bulletin of the Seismological Society of America

By:
, ,
DOI: 10.1016/j.jsames.2012.06.002

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Abstract

We present a new set of contour maps of the seismic structure of South America and the surrounding ocean basins. These maps include new data, helping to constrain crustal thickness, whole-crustal average P-wave and S-wave velocity, and the seismic velocity of the uppermost mantle (Pn and Sn). We find that: (1) The weighted average thickness of the crust under South America is 38.17 km (standard deviation, s.d. ±8.7 km), which is ∼1 km thinner than the global average of 39.2 km (s.d. ±8.5 km) for continental crust. (2) Histograms of whole-crustal P-wave velocities for the South American crust are bi-modal, with the lower peak occurring for crust that appears to be missing a high-velocity (6.9–7.3 km/s) lower crustal layer. (3) The average P-wave velocity of the crystalline crust (Pcc) is 6.47 km/s (s.d. ±0.25 km/s). This is essentially identical to the global average of 6.45 km/s. (4) The average Pn velocity beneath South America is 8.00 km/s (s.d. ±0.23 km/s), slightly lower than the global average of 8.07 km/s. (5) A region across northern Chile and northeast Argentina has anomalously low P- and S-wave velocities in the crust. Geographically, this corresponds to the shallowly-subducted portion of the Nazca plate (the Pampean flat slab first described by Isacks et al., 1968), which is also a region of crustal extension. (6) The thick crust of the Brazilian craton appears to extend into Venezuela and Colombia. (7) The crust in the Amazon basin and along the western edge of the Brazilian craton may be thinned by extension. (8) The average crustal P-wave velocity under the eastern Pacific seafloor is higher than under the western Atlantic seafloor, most likely due to the thicker sediment layer on the older Atlantic seafloor.

Geospatial Extents

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Seismic structure of the crust and uppermost mantle of South America and surrounding oceanic basins
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1016/j.jsames.2012.06.002
Volume
42
Year Published:
2013
Language:
English
Publisher:
Elsevier
Publisher location:
Amsterdam, Netherlands
Contributing office(s):
Earthquake Science Center
Description:
17 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
260
Last page:
276
Other Geospatial:
South America