Journal of Geophysical Research

The Central Andes subduction zone has been the theater of numerous large megathrust earthquakes since the beginning of the 21th Century, starting with the 2001 Mw=8.4 Arequipa, 2007 Mw=8.0 Pisco and 2014 Mw=8.1 Iquique earthquakes. Here, we present an analysis of 47 permanent GNSS time series and 26 survey GNSS measurements acquired in Central-South Peru between 2007 and 2022 to better understand the frictional properties of the megathrust interface. Using a trajectory model that mimics the different phases of the cycle, we extract a coherent interseismic GNSS field at the scale of the Central Andes from Lima to Arica (12°S - 18.5°S). GNSS-derived interseismic models on a 3D slab geometry indicate that the level of locking is relatively high and concentrated between 20 and 40 km depth. Locking distributions indicate a high spatial variability of the coupling along the trench axis, with the presence of many locked patches that spatially correlate with the seismic segmentation of that subduction. Our study confirms the presence of a creeping segment where the Nazca Ridge enters in subduction; we also observe a more tenuous apparent decrease of coupling related to the Nazca Fracture Zone (NFZ). However, since the Nazca Ridge appears to behave as a strong barrier, the NFZ is relatively weak and less efficient to arrest seismic rupture propagation. Considering various uncertainties on the data and models, we discuss the implication of our coupling estimates with the size and timing of large and great megathrust earthquakes considering both deterministic and probabilistic approaches. We estimate that the South Peru segment could host a maximum magnitude Mmax 9.0 earthquake depending principally on the considered seismic catalog and the seismic/aseismic slip ratio.

Interseismic coupling distribution from our inversion of interseismic velocities in the PS frame, with three different smoothing (λ = 15, 30 and 200 km). Slab contours (dashed lines) are reported every 20 km depth, from the Slab2 model (Hayes et al. 2018). The interseismic coupling is highly heterogeneous reflecting strong variations of the frictional properties of the slab interface. Thus, there are four highly-coupled areas: a very-highly coupled area close to Lima, a less highly-coupled area near Ica, a large band of high-coupling between the Nazca Ridge and the Nazca Fracture Zone, and a highly-coupled area between the Nazca Fracture Zone and the Arica bend. Discontinuities can be observed where the Nazca Ridge and the Nazca Fracture Zone are subducting below the South America plate. The approximate rupture area of the Mw=8.4 2001 Arequipa has been estimated in this study, while the Mw=8.0 2007 Pisco earthquake rupture is reported from Chlieh et al. (2011). On the right panel are displayed the moment deficit rate by latitude for models in the PS and SSA frame, and with various smoothing (λ = 15, 30 and 200 km), computed over 10-km wide segments. Patches with gray hachure pattern depict areas that are not well resolved by the model. Rupture extents from major seismic events are reported as blue segments.

Updated on 3 April 2023