Abstract EN:

The chilean subduction zone between the Nazca and South American plates is an ideal laboratory to understand the processes that take place on such a plate boundary. Measuring the elastic deformation of the upper plate during the interseismic phase using GPS can help assessing the degree of locking between both plates. We calculate the kinematic coupling using a simple backslip model. My aim was to obtain the coupling distribution along the entire chilean trench (18-38°S) and to compare it to seismotectonic segmentation of the megathrust. I collected all the published interseismic velocities and combined them into a single data set. New data were collected and processed since 2009 on new or renovated campaign networks. We obtain a new date set on more than a hundred benchmarks. Those data were used to map precisely the coupling on the interface. It strongly varies both along strike and along dip and draws a segmentation of the megathrust. The highly coupled segments correlate well with historical megathrust earthquakes and intersegments, that are low coupled, correlate with zones that behave as barriers. The Maule earthquake that occured on February 27, 2010 ruptured a highly locked segment and stopped in low coupled intersegment areas. It gave us new insights on the relationship between apparent coupling and mechanical behavior of the subduction interface. Coupling maps should help estimating the seismic hazard along the Chilean subduction zone. In particular, we show here that the seismic hazard in the North Chile seismic gap may be lower than expected. Finally, Loa, Paranal and Atacama regions are zones that may rupture alone with a big subduction earthquake.