Andean structural control on interseismic coupling in the North Chile subduction zone
Segmentation can influence the extent of earthquake rupture and event magnitude: large megathrust earthquakes result from total rupture of relatively continuous segments of the subduction interface. Segmentation is attributed to variations in the frictional properties of the seismogenic zone or to topographic features on the down-going plate. Structures in the overriding plate may also influence segmentation but their importance has been dismissed. Here, we investigate the links between interface segmentation at the North Chile seismic gap and a crustal-scale fault structure in the overriding plate that forms a coastal scarp of about 1 km in height. We use satellite interferometric synthetic aperture radar (InSAR) and Global Positioning System (GPS) data to measure interseismic surface deformation between 2003 and 2009 and compare the deformation with rupture extent during well-documented earthquakes. From these data we infer the degree of coupling and segmentation at depth. We find that along a 500-km-long segment, the base of the strongly coupled seismogenic zone correlates with the line of the surface coastal scarp and follows the outline of the Mejillones Peninsula. This correlation implies that large-scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth. We therefore suggest that the occurrence of megathrust earthquakes in northern Chile is controlled by the surface structures that build Andean topography.
Additional Information© 2013 Macmillan Publishers Limited. Received 01 August 2012. Accepted 19 March 2013. Published online 28 April 2013. This work was performed in the frame of the French/Chilean international collaboration (CNRS/CONICYT LIA 'Montessus de Ballore'). We thank the European Space Agency (ESA) for providing the ENVISAT images (project AO-720). This work was made possible thanks to the funding of the French National Research Agency (ANR-05-CATT-014, ANR-06-CATT-010-01), CNRS/INSU PNTS project, BQR IPGP and the LABEX UnivEarthS (Sorbonne Paris Cité, IPGP). Development and analysis of the CAnTO GPS network was partly supported by the Gordon and Betty Moore Foundation. We are very grateful to the many people who contributed to the development and maintenance of the permanent GPS network in North Chile and the associated database, in particular C. Aranda, S. Barrientos, J. Campos, J. B. de Chabalier, O. Charade, D. Comte, A. Delorme, B. Glass, J. Galetzka, E. Maureira, A. Nercessian, M. Olcay, I. Ortega, J. C. Ruegg, C. Valderas-Bermejo and C. Vigny. Author contributions: M.B-P. processed InSAR data, analysed InSAR and cGPS time-series, and did the modelling. A.S. designed the study, collected the GPS data, and supervised geodetic analysis and modelling. R.A. did the geomorphologic analysis and geological interpretation. D.C. collected the GPS data and contributed to the geological interpretation. J.G. collected and processed GPS data. M.S. contributed to the data collection, geodetic analysis and modelling. The paper was co-written by A.S., R.A. and M.B-P. All authors discussed the results and commented on the paper. Competing financial interests The authors declare no competing financial interests.
Supplemental Material - ngeo1802-s1.pdf