Power-law correlations of landslide areas in central Italy

We have studied the frequency–area statistics of landslides in central Italy. We consider two data sets. Data set A contains 16 809 landslide areas in the Umbria–Marche area of central Italy; they represent a reconnaissance inventory of very old, old, and recent (modern) landslides. The noncumulative frequency–area distribution of these landslides correlates well with a power-law relation, exponent −2.5, over the range 0.03 km2<AL<4 km2. Data set B contains 4233 landslides that were triggered by a sudden change in temperature on 1 January 1997, resulting in extensive melting of snow cover. An inventory of these snow-melt-triggered landslides was obtained from aerial photographs taken 3 months after the event. These landslides also correlate well with a power-law relation with exponent −2.5, over the range 0.001 km2<AL<0.1 km2. We show that the correlation of data set B is essentially identical to the correlation of 11 000 landslides triggered by the 17 January 1994 Northridge, California earthquake. We attribute a rollover for small landslides in data set A to incompleteness of the record due to erosion and other processes, and to limitations in the reconnaissance mapping technique used to complete the inventory. On the other hand, we conclude that rollovers for small landslides in data set B and the California earthquake data are real and are associated with the surface morphology. We conclude that the power-law distribution is valid over a wide range of landslide areas and discuss possible reasons. We also discuss the contribution of the snow-melt- and earthquake-triggered landslide events to the total landslide inventory.