Landslides and Earthquakes

Earthquakes are a major cause of landslides. Landslides, in turn, are a major contributor to the damage and causalities associated with earthquakes. It is desirable to quantify this association between landslides and earthquakes. A major step in this direction was taken by Keefer (1994) who obtained an empirical relationship between the magnitude (moment) of an earthquake and the total volume of the landslides generated by the earthquake. In order to extend this quantification, we have fit a frequency-area probability distribution to three recent very well-documented and ``complete'' landslide event inventories, from different parts of the world and with different triggering mechanisms. Our proposed ``universal'' landslide probability distribution consists of a three-parameter inverse gamma distribution. One implication of this universal distribution is that the mean area of the landslides in the distribution is 3,070 m², and is independent of both the total number (N_LT) and total area (A_LT) of landslides that occurred during the triggered landslide event. To further quantify landslide events we introduce the landslide-event magnitude scale M_L = log(N_LT). Using our universal probability distribution, M_L can be determined from a partial inventory of the largest landslides that occur during a landslide event. Using the largest 10% of landslides that occur during our ``complete'' inventories, the predicted values for N_LT and A_LT are within 0.1--15% of the actual values for the complete inventory. Finally, we relate our landslide magnitude to earthquake magnitude, convert landslide areas to volumes using an approximate relationship, and determine an analytic expression for the rate of erosion, based on the Gutenberg-Richter frequency-magnitude of earthquakes in the region.