Earthquake contributions to coastal cliff retreat

Abstract. Modeling suggests that steep coastal regions will experience increasingly rapid erosion related to climate-change-induced sea level rise. Earthquakes can also cause intense episodes of cliff retreat, but coseismic failures are rarely captured in the historical record used calibrate most retreat forecast models. Here, we disaggregate cliff-top strong ground motion and non-seismic sources, providing a unique window into earthquake contributions multidecadal retreat. Widespread landsliding up ca. 19 m occurred area Conway Flat during 2016 Kaikōura (New Zealand) despite relatively low (ca. 0.2 g) peak accelerations. While has been spatially temporally variable over record, aerial imagery large earthquake-induced landslide-triggering events disproportionately contribute an average 0.25 yr−1 at Flat. The represents 24 % total 72 years 39 56 years. Additionally, infer significant between 1950 1966 is result local seismicity. Together these two account for 57 Earthquake-related debris piles base cliffs have rapidly eroded since (more than 25 loss volume 5 years), there likely be little evidence within next decade. In with similar lithologic conditions, past widespread single-event may limited or non-existent. results demonstrate projections using records significantly underestimate true rates seismically active regions.