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Seismic reflection image revealing offset of Andean subduction-zone earthquake locations into oceanic mantle

Nature volume 397, pages 341–344 (1999)Cite this article

Abstract

Since the advent of plate-tectonic theory over 30 years ago1,2, the geometries of subduction zones have been constrained mainly by the spatial distribution of earthquake hypocentres, known as Wadati–Benioff zones. This is due to the fact that, despite the existence of a wealth of shallow seismic reflection and refraction data, very few high-resolution images of deep subduction-zone structure have been obtained. The few attempts to image these structures (see, for example, refs 3,4,5) were restricted to marine surveys, with the exception of one experiment6,7, and none of these studies was successful at mapping structure to more than 30–40 km depth. The association of intermediate-depth earthquakes with a given layer of subducting oceanic lithosphere has therefore remained largely unresolved8. Here we report seismic reflection and refraction data across the central Andean subduction zone, which image the subduction boundary to a depth of 80 km. We show, by comparing the location of this boundary with earthquake hypocentres precisely located by a temporary seismic array in the region, that most of the intermediate-depth seismicity is offset into the subducting oceanic mantle, rather than lying within the crust or on the subduction-zone boundary itself, as has often been assumed.

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Figure 1: Location map of the ANCORP seismic reflection and refraction survey and the earthquake monitoring network (stars) in the central Andes.
Figure 2: Shotgather from the Quebrada Blanca mine (36 t explosives from quarry blast).
Figure 3: Seismic reflection image and seismicity of central Andean forearc and subduction zone from the ANCORP experiment.
Figure 4: Interpretation diagram showing downgoing Nazca plate.

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Acknowledgements

We thank the Chilean Navy for providing a vessel for firing the marine shots. We also thank the following for logistical support: the mining companies Compañia Minera Punta de Lobos SA, Compañia Minera Doña Inés de Collahuasi and Compañia Quebrada Blanca, and the local authorities Carabineros de Chile, Zona de Tarapacá y Antofagasta (Retenes de Ollagüe, Ujina), Instituto Geográfico Militar La Paz and Ministerio de Hacienda y Desarrollo Económico, Secretaia Nacional de Minera, Bolivia. A great deal of the success of this project is due to the more than 100 helpers and field operators from all three countries. This Letter benefited substantially from constructive criticism by R. Clowes. The ANCORP '96 project was funded by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF, Bonn) within the DEKORP programme (Deutsches Kontinentales Reflexionsseismisches Program) and by the Deutsche Forschungsgemeinschaft (DFG, Bonn) within the Collaborative Research Center 267 (SFB 267—Deformationsprozesse in den Anden).

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Author notes

  1. Onno Oncken, Ewald Lschen, James Mechie, Stephan Sobolev, Albrecht Schulze, Cristoph Gaedicke, Steffen Grunewald, Jens Bribach, Günter Asch (GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany) Peter Giese, Peter Wigger, Michael Schmitz, Stefan Lueth, Ekkehard Scheuber, Christian Haberland, Andreas Rietbrock, Hans-Jürgen Götze, Heinrich Brasse, Regina Patzwahl (Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany) Guillermo Chong, Hans-Gerhard Wilke, Gabriel Gonzalez, Arturo Jensen (Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile) Manuel Araneda (Universidad de Chile, Casilla 2777, Santiago) Hugo Vieytes (ENAPEmpresa Nacional Del Petróleo, Casilla 247, Punta Arenas, Chile) Gerardo Behn (CODELCO, Calle Huréfanos 1270, Casilla 150-D, Santiago, Chile) Eloy Martinez (ANDINA-SAM, Casilla 1659, SantaCruz, Bolivia) Reinhard Rössling, José Amador (SERGEOMIN, Casilla 2729, La Paz, Bolivia) Edgar Ricaldi (Universidad Mayor de San Andres, Casilla 4836, La Paz, Bolivia) Hern´n Chumacero (Universidad Autónoma Tomás Fris, Casilla 5, Potosí, Bolivia) Ral Luterstein (CNEAComisión Nacional de Energía Atomica, Avda. del Libertador 8250, 1429 Buenos Aires, Argentina).

    • Onno Oncken: Correspondence and requests for materials should be addressed to O.O.

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      Onno Oncken: Correspondence and requests for materials should be addressed to O.O.

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      The ANCORP Working Group. Seismic reflection image revealing offset of Andean subduction-zone earthquake locations into oceanic mantle. Nature 397, 341–344 (1999). https://doi.org/10.1038/16909

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