Earthquake-induced landslides and their effects on alluvial fans

Earthquakes as small as magnitude 4.0 may dislodge landslides from suscepti ble slopes, and larger earthquakes can generate tens of thousands of landsl ides throughout areas of hundreds of thousands of square kilometers, produc ing billions of cubic meters of loose, surficial sediment. These landslides can have significant geomorphic effects that vary depending on the landsli de characteristics and materials, and on the settings in which the landslid es occur. A review of data from historical earthquakes indicates that the l andslides they generated can be classified into 14 different types. These i nclude highly disaggregated and fast-moving falls, disrupted slides, and av alanches; more coherent and slower-moving slumps, block slides, and earth s lides; and lateral spreads and flows that involve partly to completely liqu efied material. Rock falls, disrupted rock slides, and disrupted slides of earth and debris are the most abundant types of earthquake-induced landslid es, whereas earth hows, debris flows, and avalanches of rock, earth, or deb ris typically transport material the farthest, Because of their abundance o r long distances of transport, these landslides generally have the greatest effects on the landscape during and after earthquakes. Landslide effects o n alluvial fans include direct deposition of material on fan surfaces; fiss uring and displacement of fan materials; alterations in drainage basins suc h as devegetation, denudation, and changes in channel networks; and generat ion of large amounts of sediment that may be transported to fans by post-ea rthquake water flows or debris flows.