Tectonic processes responsible for various wavelengths of permanent deformation on the western coast of South America

Abstract

<p><strong>Abstract.</strong> The tectonically active western coast of South America is characterized by the accumulation of deformation that contributes to permanent uplift of the Andean forearc at glacial-cycle timescales. However, the individual mechanisms responsible for long-term coastal uplift are still debated, mostly because analyses at continental-scale have not been carried out as yet. In coastal realms, permanent deformation is often estimated from marine terraces, which depict the interplay between wave erosion, tectonic uplift, and sea-level changes. Based on ~2000 elevation measurements of last interglacial marine terraces, we performed wavelength analyses using fast Fourier transforms. We compared the resulting uplift-rate signal with various tectonic processes and subduction parameters associated with the accumulation of permanent deformation. We detected a constant background signal of uplift along the South American margin (median rate: 0.22 mm/yr), which is disturbed by short-, intermediate- and long-wavelength changes between ~20 and ~800 km wavelengths, with the most prominent wavelengths at scales of ~500 km. Similarities between the wavelength spectra of uplift rate and signals from tectonic parameters suggest potential correlations, although multiple individual mechanisms usually contribute to a larger wavelength peak or to a certain range of wavelengths. For instance, crustal faulting is responsible for short-wavelength deformation (<100 km) and strong megathrust earthquakes (M<sub>W</sub>>7.5) mostly cover wavelength ranges from ~100 to 200 km, despite reaching wavelengths over 600 km as well. The subduction of bathymetric anomalies and the extent of interseismic locking correlate with intermediate wavelengths (~200 to ~500 km), whereas residual gravity anomalies, basal friction, and background seismicity correlate with long-wavelength deformation (>500 km). We suggest that the constant background signal of uplift rate results from two possible mechanisms: (a) a combination of multiple processes acting at different wavelengths, times and locations over millennial timescales or (b) a single unidentified process acting homogeneously along the western South American margin. With this study, we highlight the application of novel signal analysis approaches to elucidate the mechanisms driving surface deformation in subduction zones on different spatial and temporal scales.</p>