Geomorphic Impacts of Large Earthquakes

Abstract

Large earthquakes can generate dramatic changes in tectonically-active landscapes. The largest of these are located mainly—but not exclusively—on long, well-defined faults, and the resulting ground motion can affect earth surface processes over large areas and for long periods of time. Coseismic ground displacement and shaking in both the mainshock and in the consequent aftershock sequence deform the landscape and cause ground failures in the form of landslides, liquefaction and lateral spreading. While ground deformation in individual earthquakes is usually meter-scale, cumulative displacements over many earthquakes can give rise to dramatic landforms. Coseismic ground failures can involve many millions of cubic meters of material, and can trigger substantial and long-duration cascades of consequential landscape changes. As a result, large earthquakes can, both singly and cumulatively, affect and interact with mass movement, river, glacial and coastal processes to generate characteristic landscape signatures such as deep-seated landslide source areas, landslide dams, episodically-incised alluvial fanheads, widespread river aggradation and avulsion, large terminal moraines unrelated to climate change, and coastal ridges. More subtle features include sackungen, ridge-top shattering, river and terrace offsets, and sand blows or other liquefaction-related surface deformation. Many of the processes that form these features have hazard implications for societal assets and commerce, so understanding the dynamics of seismically-active landscapes is critically important for disaster impact reduction. Further, seismic geomorphology can be back-analysed for paleoseismological purposes to better define the underlying seismic hazard.