Tectonic Uplift Outpaces Modern Sea‐Level Rise: Recovery of the Valdivia Estuary Following >2‐m Subsidence During the M9.5 1960 Chile Earthquake

Abstract

The M9.5 1960 Chile earthquake, the largest instrumentally recorded, caused over 2 m of coseismic subsidence in the Valdivia estuary, converting fluvial terraces into open water and, later, tidal marshes. We quantify the decadal‐scale post‐seismic recovery of these estuarine wetlands using historical aerial photography, Landsat/Sentinel imagery, GNSS‐derived vertical land motion, tide‐gauge and satellite altimetry sea‐level records, and dated sediment cores. Open water area expanded ∼8.8‐fold after the earthquake and has since contracted from ∼94 km ² in 1985 to 61 km ² in 2024, following a strongly linear trend ( r  = −0.97) implying recovery to the pre‐earthquake fluvial extent by ∼2056. Interseismic uplift across the estuary (6.2–9.5 mm/yr) currently exceeds regional absolute sea‐level rise (∼2.3 mm/yr), producing a falling relative sea level that correlates strongly with vegetation expansion across tributary basins, indicating tectonic vertical land motion, rather than climate forcing, dominates wetland recovery at this timescale. Sediment accretion rates increase after subsidence and then decrease from subtidal to intertidal facies, reflecting the open water‐to‐marsh transition during interseismic emergence. A Monte Carlo projection combining vertical land motion, accretion, and IPCC sea‐level scenarios estimates the estuary will return to supratidal elevations by a median year of 2063 (5%–95% range 2047–2099), with coseismic subsidence magnitude and sea‐level rise dominating the uncertainty. These findings underscore the need to account for seismic‐cycle vertical land motion alongside climate‐driven sea‐level rise when assessing the long‐term resilience and carbon‐storage capacity of coastal wetlands in tectonically active subduction zones.