Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm.
For example, the number of landslides triggered by a given event is almost always greatly underestimated. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. This paper traces thehistorical development of knowledge derived from these investigations. Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides.
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