From Elastic Strain to Permanent Uplift Along the North Chilean Forearc

Along-strike variations in megathrust coupling modulate forearc deformation through both elastic, seismic-cycle processes and permanent tectonic uplift. Yet the degree to which short-term interseismic deformation is translated into long-term geomorphic expression remains poorly constrained. We investigate this relationship along the hyperarid North Chilean forearc using Sentinel-1 InSAR time series and a set of geomorphic uplift proxies, including marine terraces, coastal topography, and alluvial fan slopes. The preservation of landforms allows direct comparison between geodetic and geomorphic signals across spatial and temporal scales.

The relationship between geodetic uplift rates and long-term uplift indicators varies along strike and becomes weak or alternates between positive and negative correlations in the Mejillones Peninsula region. This peninsula constitutes a tectonic hinge separating two seismotectonic segments characterized by distinct deformation patterns. Alternating correlations and anticorrelations between geodetic uplift and uplifted marine traces imply episodic uplift governed by the interplay of interseismic and coseismic vertical motions. Coastal alluvial fan slopes correlate with geodetic uplift only in the  segment north of Mejillones towards the north, whereas south of it their independence from uplift suggests a dominant climatic control. The geodetic uplift rates and coastal topography preserve similar large-scale trends while differing in finer-scale, and the local correlation remains mostly positive across the latitude range. Upper-plate faults align with the north–south aligned inflection zone of geodetic uplift, suggesting that their geometry and distribution may be influenced by regional bending and strain gradients across the uplift–subsidence transition. Their low slip-rates may indicate that these faults do not accommodate significant long-term plate motion; instead, they remain largely quiescent interseismically and are preferentially activated during megathrust earthquakes through transient stress transfer. Our results suggest that long-wavelength, long-term deformation dominates forearc topography, whereas short-wavelength, seismic-cycle deformation adds variability that may be preserved differently across geomorphic features.