Uplift rate transients at subduction margins due to earthquake clustering

Abstract

AbstractCoastal uplift is common in continental fore‐arc systems, with elevated paleoshorelines indicating that uplift rates can vary dramatically over time on individual margins. The origins of these changes in uplift rates are examined using a global data set of paleoshorelines together with 2‐D numerical models of subduction systems. Empirical paleoshoreline data (N = 282) from eight subduction margins indicate that uplift rates are generally not steady state and varied by up to a factor of 20 during the late Quaternary (≤125 ka). On many subduction margins uplift rates increase to the present day, a finding which we attribute to sampling bias toward those locations where Holocene uplift rates have been highest (with respect to other global margins which have undergone fast subsidence or no vertical motion—e.g., a property akin to the so‐called Sadler effect). Paleoshorelines and 2‐D models suggest that transient uplift rates at subduction margins are mainly a short‐term (<20 ka) phenomenon that cannot be accounted for by plate‐boundary scale processes such as changes in the rates of plate convergence, sediment underplating or isostatic unloading. Instead, time‐variable uplift rates are ascribed to temporal clustering of large‐magnitude earthquakes on upper plate faults and, to a lesser extent, the subduction thrust. The potential for future damaging earthquakes and tsunamis may have been underestimated at active subduction margins with no measureable Holocene uplift, and in such cases, late Quaternary paleoshorelines could provide an important constraint for hazard analysis.