Tectonics as a Regulator of Shoreline Retreat and Rocky Coast Evolution Across Timescales

Abstract Rocky coast morphology is shaped by interactions between wave action, sea level, and tectonics over millennial time scales. However, a clear and quantifiable signature of tectonic uplift on decadal to centennial shoreline retreat rates is outstanding. We isolate the contribution of tectonic uplift to setting shoreline retreat and shore platform morphology from other marine and geologic drivers across the West Coast of the USA. Specifically, we find that decadal‐scale tectonic uplift, derived from tide gauge records, exerts a significant and measurable control on shoreline retreat rates. Additional influences from wave action, shore platform morphology, and tidal range further contribute to the regional patterns in coastal erosion, and together these factors enable accurate prediction of retreat rates using a multivariate model. Our analysis also reveals robust, time‐scale dependent relationships between uplift rate, shore platform morphology, and shoreline retreat. On decadal time scales, rapid tectonic uplift acts as a buffer, shielding the shore from wave action, slowing retreat, and corresponding with narrow shore platforms. On millennial time scales, higher uplift rates relate to wider shore platforms, reflecting greater cumulative shoreline retreat. These observations likely reflect the effects of episodic, seismically driven subsidence, which shifts wave action landward, enhancing wave‐driven erosion. Through repeated cycles of uplift and subsidence, the seismic cycle amplifies both shore platform development and long‐term retreat. Together, these findings highlight the critical role of tectonics in shaping shoreline retreat and driving landscape evolution timescales on active margins.