Crustal deformation and fault slip during the seismic cycle in the North Chile subduction zone, from GPS and InSAR observations

Abstract

SUMMARY The different phases of the earthquake cycle can produce measurable deformation of the Earth's surface. This work is aimed at describing the evolution of that deformation in space and time, as well as the distribution of causal slip on the fault at depth. We have applied GPS and synthetic aperture radar (SAR) interferometry (InSAR) techniques to northern Chile, where fast plate convergence rates are associated with large subduction earthquakes and extensive crustal deformation. The region of northern Chile between 18°S and 23°S is one of the most important seismic gaps in the world, with no rupture having occurred since 1877. In 1995, the Mw= 8.1 Antofagasta earthquake ruptured the subduction interface over a length of 180 km in the region immediately to the south of this 450 km long gap. The coseismic deformation associated with this event has been documented previously. Here we use GPS position time‐series for 40 benchmarks (measured between 1996 and 2000) and ERS SAR interferograms (for the interval between 1995 and 1999) to map both the post‐seismic deformation following the 1995 event and the ongoing interseismic deformation in the adjacent gap region. In the seismic gap, the interseismic velocities of 20–30 mm yr−1 to the east with respect to South America are mapped. Both the GPS and the InSAR measurements can be modelled with 100 per cent coupling of the thrust interface of the subduction to a depth of 35 km, with a transition zone extending down to 55 km depth. The slip rate in that zone increases linearly from zero to the plate convergence rate. South of the gap, the interferometric map shows interseismic deformation superimposed with deformation following the 1995 earthquake and covering the same area as the coseismic deformation. Some 40 per cent of this deformation is related to seismic activity in the 3.3 yr following the 1995 event, in particular slip during a Mw= 7.1 earthquake in 1998. However, most of the signal (60 per cent) corresponds to post‐seismic deformation resulting from widespread aseismic slip in the subduction interface. The afterslip appears to have occurred down‐dip in the transition zone at 35–55 km depth and to have propagated laterally northwards at 25–45 km depth under the Mejillones Peninsula, which is a prominent geomorphological feature at the boundary between the 1877 and 1995 rupture zones. We propose a simple slip model for the seismic cycle associated with the Antofagasta earthquake, where the transition zone alternates between aseismic shear and seismic slip.

Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

“…Nevertheless, the area of largest coseismic slip in the 1995 Antofagasta earthquake deduced from GPS data [Klotz et al, 1999;Pritchard et al, 2002;Xia et al, 2003;Chlieh et al, 2004] is almost identical with the slip area identified by local seismological parameters from investigating the aftershock sequence [Sobiesiak, 2000]. However, this local study showed a more detailed picture of the coseismic slip area separated in two patches of large slip values.…”

Constricción neógena en la Cordillera de la Costa, norte de Chile: neotectónica y datación de superficies con 21Ne cosmogónico

“…1991; Beck et al, 1993;Tikoff y Teyssier, 1994;Teyssier et al, 1995;McCaffrey, 1994McCaffrey, , 1996Wang et al, 2003;Yáñez y Cembrano, 2004;Chlieh et al, 2004;Tassara y Yáñez, 2003;Tassara, 2005). Los antecedentes expuestos en este trabajo no permiten explicar en detalle la interrelación entre los diferentes factores que condicionan el estilo de deformación observado.…”

Scenario Source Models and Strong Ground Motion for Future Mega‐earthquakes: Application to Lima, Central Peru

“…To improve the seismic-hazard assessment for such rare events, it may be useful to incorporate other kinds of information such as crustal deformation at plate margins. In recent years, the development of Global Positioning System (GPS) and satellite radar interferometry make it possible to measure the strain buildup associated with plate coupling in many earthquakeprone regions around the world (Chlieh et al, 2004(Chlieh et al, , 2011Béjar-Pizarro et al, 2013). Recent studies have suggested that subducting plates are either locked or creeping aseismically, and that a patchwork of locked or coupled regions during the interseismic period may be related with asperities of earthquakes (Konca et al, 2008;Moreno et al, 2010;Perfettini et al, 2010;Loveless and Meade, 2011).…”