Space geodetic observations of Nazca-South America convergence across the central Andes

Science

Volumn 279, Issue 5349, 1998, Pages 358-362

  Norabuena, Edmundo ^a,b   Leffler Griffin, Lisa ^c   Mao, Ailin ^b   Dixon, Timothy ^b   Stein, Seth ^c   Sacks, I Selwyn ^d   Ocola, Leonidas ^a   Ellis, Michael ^e  

^a INSTITUTO GEOFÍSICO DEL PERÚ   (Peru)

^b UNIVERSITY OF MIAMI   (United States)

^c NORTHWESTERN UNIVERSITY   (United States)

^d GEOPHYSICAL LABORATORY   (United States)

^e UNIVERSITY OF MEMPHIS   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

COLLISION ZONE; GEODESY; PLATE MOTION;

ARTICLE; EARTHQUAKE; GEOGRAPHY; GEOLOGY; PRIORITY JOURNAL; SPACE;

SOUTH AMERICA;

EID: 0032535957     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.279.5349.358     Document Type: Article

References (65)

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19. F. Megard, in The Anatomy of Mountain Ranges, J. Schaer and J. Rogers, Eds. (Princeton Univ. Press, Princeton, NJ, 1987), pp. 179-204; B. Sheffels, Geology 18, 812 (1990); M. Schmitz, Tectonics 13, 484 (1994); M. Sebrier et al., ibid. 7, 895 (1988); D. Roeder, ibid., p. 23; T. Sempere et al., Geology 18, 946 (1990); R. Allmendinger et al., Annu. Rev. Earth Planet. Sci. 25, 139 (1997).
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21. F. Megard, in The Anatomy of Mountain Ranges, J. Schaer and J. Rogers, Eds. (Princeton Univ. Press, Princeton, NJ, 1987), pp. 179-204; B. Sheffels, Geology 18, 812 (1990); M. Schmitz, Tectonics 13, 484 (1994); M. Sebrier et al., ibid. 7, 895 (1988); D. Roeder, ibid., p. 23; T. Sempere et al., Geology 18, 946 (1990); R. Allmendinger et al., Annu. Rev. Earth Planet. Sci. 25, 139 (1997).
22. F. Megard, in The Anatomy of Mountain Ranges, J. Schaer and J. Rogers, Eds. (Princeton Univ. Press, Princeton, NJ, 1987), pp. 179-204; B. Sheffels, Geology 18, 812 (1990); M. Schmitz, Tectonics 13, 484 (1994); M. Sebrier et al., ibid. 7, 895 (1988); D. Roeder, ibid., p. 23; T. Sempere et al., Geology 18, 946 (1990); R. Allmendinger et al., Annu. Rev. Earth Planet. Sci. 25, 139 (1997).
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24. M. Beck, Phys. Earth Planet. Inter. 68, 1 (1991); R. McCaffrey, J. Geophys. Res. 97, 8905 (1992).
25. GPS data were analyzed following T. Dixon et al. [J. Geophys. Res. 102, 12017 (1997)]. We used high-precision nonfiducial satellite orbits and the Jet Propulsion Laboratory GIPSY analysis software to estimate site velocities in the International Terrestrial Reference Frame (ITRF-94) reference frame (10). Site velocities were estimated from least squares fits to daily positions weighted by the scaled formal error. Data from one site (CASM, Fig. 2) were anomalous, perhaps because of errors in setting up the GPS antenna over the geodetic monument. Sites, data, and uncertainties are given at www.sciencemag.org/feature/data/975403.shl
26. GPS data were analyzed following T. Dixon et al. [J. Geophys. Res. 102, 12017 (1997)]. We used high-precision nonfiducial satellite orbits and the Jet Propulsion Laboratory GIPSY analysis software to estimate site velocities in the International Terrestrial Reference Frame (ITRF-94) reference frame (10). Site velocities were estimated from least squares fits to daily positions weighted by the scaled formal error. Data from one site (CASM, Fig. 2) were anomalous, perhaps because of errors in setting up the GPS antenna over the geodetic monument. Sites, data, and uncertainties are given at www.sciencemag.org/feature/data/975403.shl
27. Plate motions are specified by Euler (angular velocity) vectors giving either the relative motion between a plate pair or the absolute motion of an individual plate. These vectors can now be derived from space geodetic data and were previously derived from data recording plate motions averaged over the past few million years [C. Chase, Geophys. J. 29, 117 (1972); J. Minster et al., ibid. 36, 541 (1974)]. ITRF-94, a reference frame for space geodetic data [C. Boucher, IERS Technical Note 20 (Observatoire de Paris, Paris, 1996)], is designed to agree on average with the absolute plate motion model NNR NUVEL-1A, termed NNR-A. The latter is a revision of model NNR, derived by combining the assumption of no net torque on the lithosphere [D. Argus and R. Gordon, Geophys. Res. Lett. 18, 2039 (1991)] with global relative plate motion model NUVEL-1 [C. DeMets et al., Geophys. J. Int. 101, 425 (1990)], reflecting a change in the magnetic anomaly time scale subsequent to the publication of NUVEL-1. NUVEL-1A and NNR-A predict plate motion directions identical to those for NUVEL-1 and NNR NUVEL-1, but 4% slower [C. DeMets et al., Geophys. Res. Lett. 21, 2191 (1994)]. Because rate data in the models come from ridges, the predicted rates across subduction zones are derived indirectly by the closure of plate circuits. Space geodetic velocities in ITRF-94 can be compared with plate motions predicted by NNR-A, and relative motions are typically compared with NUVEL-1A (30).
28. Plate motions are specified by Euler (angular velocity) vectors giving either the relative motion between a plate pair or the absolute motion of an individual plate. These vectors can now be derived from space geodetic data and were previously derived from data recording plate motions averaged over the past few million years [C. Chase, Geophys. J. 29, 117 (1972); J. Minster et al., ibid. 36, 541 (1974)]. ITRF-94, a reference frame for space geodetic data [C. Boucher, IERS Technical Note 20 (Observatoire de Paris, Paris, 1996)], is designed to agree on average with the absolute plate motion model NNR NUVEL-1A, termed NNR-A. The latter is a revision of model NNR, derived by combining the assumption of no net torque on the lithosphere [D. Argus and R. Gordon, Geophys. Res. Lett. 18, 2039 (1991)] with global relative plate motion model NUVEL-1 [C. DeMets et al., Geophys. J. Int. 101, 425 (1990)], reflecting a change in the magnetic anomaly time scale subsequent to the publication of NUVEL-1. NUVEL-1A and NNR-A predict plate motion directions identical to those for NUVEL-1 and NNR NUVEL-1, but 4% slower [C. DeMets et al., Geophys. Res. Lett. 21, 2191 (1994)]. Because rate data in the models come from ridges, the predicted rates across subduction zones are derived indirectly by the closure of plate circuits. Space geodetic velocities in ITRF-94 can be compared with plate motions predicted by NNR-A, and relative motions are typically compared with NUVEL-1A (30).
29. Plate motions are specified by Euler (angular velocity) vectors giving either the relative motion between a plate pair or the absolute motion of an individual plate. These vectors can now be derived from space geodetic data and were previously derived from data recording plate motions averaged over the past few million years [C. Chase, Geophys. J. 29, 117 (1972); J. Minster et al., ibid. 36, 541 (1974)]. ITRF-94, a reference frame for space geodetic data [C. Boucher, IERS Technical Note 20 (Observatoire de Paris, Paris, 1996)], is designed to agree on average with the absolute plate motion model NNR NUVEL-1A, termed NNR-A. The latter is a revision of model NNR, derived by combining the assumption of no net torque on the lithosphere [D. Argus and R. Gordon, Geophys. Res. Lett. 18, 2039 (1991)] with global relative plate motion model NUVEL-1 [C. DeMets et al., Geophys. J. Int. 101, 425 (1990)], reflecting a change in the magnetic anomaly time scale subsequent to the publication of NUVEL-1. NUVEL-1A and NNR-A predict plate motion directions identical to those for NUVEL-1 and NNR NUVEL-1, but 4% slower [C. DeMets et al., Geophys. Res. Lett. 21, 2191 (1994)]. Because rate data in the models come from ridges, the predicted rates across subduction zones are derived indirectly by the closure of plate circuits. Space geodetic velocities in ITRF-94 can be compared with plate motions predicted by NNR-A, and relative motions are typically compared with NUVEL-1A (30).
30. Plate motions are specified by Euler (angular velocity) vectors giving either the relative motion between a plate pair or the absolute motion of an individual plate. These vectors can now be derived from space geodetic data and were previously derived from data recording plate motions averaged over the past few million years [C. Chase, Geophys. J. 29, 117 (1972); J. Minster et al., ibid. 36, 541 (1974)]. ITRF-94, a reference frame for space geodetic data [C. Boucher, IERS Technical Note 20 (Observatoire de Paris, Paris, 1996)], is designed to agree on average with the absolute plate motion model NNR NUVEL-1A, termed NNR-A. The latter is a revision of model NNR, derived by combining the assumption of no net torque on the lithosphere [D. Argus and R. Gordon, Geophys. Res. Lett. 18, 2039 (1991)] with global relative plate motion model NUVEL-1 [C. DeMets et al., Geophys. J. Int. 101, 425 (1990)], reflecting a change in the magnetic anomaly time scale subsequent to the publication of NUVEL-1. NUVEL-1A and NNR-A predict plate motion directions identical to those for NUVEL-1 and NNR NUVEL-1, but 4% slower [C. DeMets et al., Geophys. Res. Lett. 21, 2191 (1994)]. Because rate data in the models come from ridges, the predicted rates across subduction zones are derived indirectly by the closure of plate circuits. Space geodetic velocities in ITRF-94 can be compared with plate motions predicted by NNR-A, and relative motions are typically compared with NUVEL-1A (30).
31. Plate motions are specified by Euler (angular velocity) vectors giving either the relative motion between a plate pair or the absolute motion of an individual plate. These vectors can now be derived from space geodetic data and were previously derived from data recording plate motions averaged over the past few million years [C. Chase, Geophys. J. 29, 117 (1972); J. Minster et al., ibid. 36, 541 (1974)]. ITRF-94, a reference frame for space geodetic data [C. Boucher, IERS Technical Note 20 (Observatoire de Paris, Paris, 1996)], is designed to agree on average with the absolute plate motion model NNR NUVEL-1A, termed NNR-A. The latter is a revision of model NNR, derived by combining the assumption of no net torque on the lithosphere [D. Argus and R. Gordon, Geophys. Res. Lett. 18, 2039 (1991)] with global relative plate motion model NUVEL-1 [C. DeMets et al., Geophys. J. Int. 101, 425 (1990)], reflecting a change in the magnetic anomaly time scale subsequent to the publication of NUVEL-1. NUVEL-1A and NNR-A predict plate motion directions identical to those for NUVEL-1 and NNR NUVEL-1, but 4% slower [C. DeMets et al., Geophys. Res. Lett. 21, 2191 (1994)]. Because rate data in the models come from ridges, the predicted rates across subduction zones are derived indirectly by the closure of plate circuits. Space geodetic velocities in ITRF-94 can be compared with plate motions predicted by NNR-A, and relative motions are typically compared with NUVEL-1A (30).
32. J. Robbins, D. Smith, and C. Ma [in Space Geodesy and Geodynamics, D. Smith and D. Turcotte, Eds. (American Geophysical Union, Washington, DC, 1993), pp. 21-36] noted the discrepancy at Easter Island between the motion estimated from SLR and that predicted by NUVEL-1A. However, data at one site provide only the two horizontal velocity compo-nents and are hence insufficient to define the three components of the Nazca plate's angular velocity vector, which requires horizontal velocity measurements at two sites (30).
33. Space geodetic data for plate motions over a few years generally agree surprisingly well with the predictions of global plate motion models derived by estimating plate motions over millions of years (2, 11, 30). However, changes in plate motions over the past 3 My have been suggested for other plate pairs both from GPS data (30) and magnetic anomalies [C. DeMets, Geophys. Res. Lett. 22, 3545 (1995)]. Because our Nazca-South America Euler vector was derived from a short time series at only two sites, it is unclear whether importance should be ascribed to the discrepancy between it and the vector from NUVEL-1 A. The discrepancy may reflect the limited data, NUVEL-1's derivation without direct data across the subduction zone, or a change in plate motions. Assessment of such possible changes should improve as additional space geodetic sites and longer time series become available.
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65. Supported by NASA's Geodynamics program and NSF's Small Grants for Exploratory Research program. We thank the Instituto Geografico Militar, Bolivia, the Institute Geofisico del Peru, and University Navstar Consortium (especially J. Richardson, B. Baker, and K. Feaux) for invaluable assistance in GPS campaigns; J. Lee and V. Berhow for assistance with site selection; S. Wdowinski, R. Russo, C. DeMets, and R. McCaffrey for helpful discussions; and the international geodetic community for maintaining a permanent GPS network with publicly available data.