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Abrupt change in the dip of the subducting plate beneath north Chile

Nature Geoscience volume 5, pages 342–345 (2012)Cite this article

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Abstract

No large tsunamigenic earthquake has occurred in north Chile since 1877 and the region has been largely recognized as a mature seismic gap1,2,3,4,5,6,7,8,9. At the southern end of the seismic gap, the 2007 Mw 7.7 Tocopilla earthquake ruptured the deeper seismogenic interface, whereas the coupled upper interface remained unbroken4,6,7. Seismological studies onshore show a gently varying dip of 20° to 30° of the downgoing Nazca plate3,6, which extends from the trench down to depths of 40–50 km. Here, we study the lithospheric structure of the subduction zone of north Chile at about 22° S, using wide-angle seismic refraction and reflection data from land and sea, complemented by hypocentre data recorded during the 2007 Tocopilla aftershocks7. Our data document an abrupt increase in the dip of the subducting plate, from less than 10° to about 22°, at a depth of approximately 20 km. The distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench, which, in turn, indicates that the subduction megathrust is not only segmented along the trench, but also in the direction of the dip. We propose that large-magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone.

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Figure 1: Seismotectonic setting of north Chile and seismic experiment.
Figure 2: Seismic velocity structure of the upper subduction zone of Tocopilla, north Chile and data example.
Figure 3: Summarized interpretation of the tomographic velocity–depth model.

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Acknowledgements

E.C-R. acknowledges the support of the Chilean National Science Foundation (FONDECYT) project 11090009. S.R and D.C acknowledge the support of FONDECYT project 1100429. We thank A. Fuenzalida, M. Lancieri and R. Madariaga for providing the hypocentre data. Marine data acquisition was financially supported by the German Ministry of Education, Science and Research. We also thank GeoForschungZentrum, Potsdam and the International Plate Boundary Observatory Chile for sharing the data.

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Authors and Affiliations

  1. Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile

    E. Contreras-Reyes, J. Jara, S. Ruiz & D. Carrizo

  2. Advanced Mining Technology Center, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile

    J. Jara & D. Carrizo

  3. GEOMAR, Helmholtz Centre of Ocean Research, Wischhofstraße 1-3, D-24148 Kiel, Germany

    I. Grevemeyer

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  1. E. Contreras-Reyes
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  5. D. Carrizo
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Contributions

E.C-R., J.J. and I.G. analysed and processed the wide-angle seismic data. E.C-R., S.R., D.C. and I.G. interpreted and wrote the paper.

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Correspondence to E. Contreras-Reyes or S. Ruiz.

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Contreras-Reyes, E., Jara, J., Grevemeyer, I. et al. Abrupt change in the dip of the subducting plate beneath north Chile. Nature Geosci 5, 342–345 (2012). https://doi.org/10.1038/ngeo1447

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