Crustal Structure Along the Rio Grande Rift from Seismic Refraction Profiles

  1. Robert E. Riecker
  1. K.H. Olsen1,
  2. G.R. Keller2 and
  3. J.N. Stewart3

Published Online: 21 MAR 2013

DOI: 10.1029/SP014p0127

Rio Grande Rift: Tectonics and Magmatism

Rio Grande Rift: Tectonics and Magmatism

How to Cite

Olsen, K.H., Keller, G.R. and Stewart, J.N. (1979) Crustal Structure Along the Rio Grande Rift from Seismic Refraction Profiles, in Rio Grande Rift: Tectonics and Magmatism (ed R. E. Riecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/SP014p0127

Author Information

  1. 1

    Geosciences Division, Los Alamos Scientific Laboratory, Los Alamos, NM 87545

  2. 2

    Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968

  3. 3

    Geosciences Division, Los Alamos Scientific Laboratory, Los Alamos, NM 87545

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1979

ISBN Information

Print ISBN: 9780875902142

Online ISBN: 9781118664988

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Keywords:

  • Chemical explosions;
  • Crustal structure;
  • Rio Grande rift;
  • Seismic refraction;
  • Surface wave dispersion data

Summary

40-station seismic refraction profile using large chemical explosions at the White Sands Missile Range as sources has been recorded along a 350 kilometer line extending north along the axis of the Rio Grande rift. The most detailed profile, obtained in 1976, originates about 40 km southeast of Socorro, New Mexico, crosses the 1975 COCORP deep reflection profile at Abo Pass 80 km from the shot, and terminates near the Colorado-New Mexico border. Interpretation of the record section indicates a crustal thickness of about 33 kilometers and an upper mantle (Pn) velocity of 7.6 km/sec uncorrected for possible dip. In contrast, refraction and surface wave dispersion ata of previous investigators in the Colorado Plateau province to the west and the Great Plains province to the east indicate somewhat thicker crust and higher Pn velocities (45 km, 7.8 km/sec and 50 km, 8.0 km/sec, respectively). This implies a moderate crustal thinning (10–15 km) under the Northern New Mexico segment of the Rio Grande rift.

The most notable feature of our 1976 record section is a strong reflection phase that exhibits high coherency over distances ranging from 20 to 130 kilometers. This phase arises from P-waves reflected from a major intracrustal layer at a depth of ∼ 21 kilometers, where the P-wave velocity changes from 6.0 km/sec to 6.4 km/sec. Traveltime and amplitude modeling with synthetic seismograms indicates the P-wave velocity contrast of 0.4 km/sec alone is insufficient to explain the high reflection amplitude; an anomalously low shear wave velocity in the reflecting layer is apparently required to match the observations. Thus, the data imply that the top of the lower crustal layer is a zone of low rigidity. Microearthquake studies by Sanford in the vicinity of Socorro have indicated the presence of a probable magma body whose upper surface lies at depths between 19 and 20 kilometers and COCORP observations west of Abo Pass have mapped a strong reflector in this depth range. Our data, from reflection points mainly to the east and south of the Sanford and COCORP areas, suggest that the Socorro magma body may be associated with a more widespread intracrustal low rigidity layer.