Supervised Method of Landslide Inventory Using Panchromatic SPOT5 Images and Application to the Earthquake-Triggered Landslides of Pisco (Peru, 2007, Mw8.0)

Pascal Lacroix,Etienne Berthier,Laurence Audin,Bilberto Zavala

doi:10.3390/rs5062590

Abstract

Earthquake is one of the dominant triggering factors of landslides. Given the wide areas covered by mega earthquake-triggered landslides, their inventory requires development of automatic or semi-automatic methods applied to satellite imagery. A detection method is here proposed for this purpose, to fit with simple datasets; SPOT5 panchromatic images of 5 m resolution coupled with a freely and globally available DEM. The method takes advantage of multi-temporal images to detect changes based on radiometric variations after precise coregistration/orthorectification. Removal of false alarms is then undertaken using shape, orientation and radiometric properties of connected pixels defining objects. 80% of the landslides and 93% of the landslide area are detected indicating small omission errors but 50% of false alarms remain. They are removed using expert based analysis of the inventory. The method is applied to realize the first comprehensive inventory of landslides triggered by the Pisco earthquake (Peru, 15/08/2007, Mw 8.0) over an area of 27,000 km2. 866 landslides larger than 100 m2 are detected covering a total area of 1.29 km2. The area/number distribution follows a power-law with an exponent of 1.63, showing a very particular regime of triggering in this arid environment compared to other areas in the world. This specific triggering can be explained by the little soil cover in the coastal and forearc regions of Peru. Analysis of this database finally shows a major control of the topography (both orientation and inclination) on the repartition of the Pisco-triggered landslides.

Highlights

Earthquake is one of the main triggering factors of landslide [1] and the most damaging trigger of landslides in terms of social cost
From the study of landslide inventories, it emerges that the triggering of landslides by earthquake is controlled by two main class of parameters: (i) the earthquake source properties (e.g., [1,3,4,5]); (ii) the site properties (e.g., [6,7,8,9])
This generic law is affected by different factors: (1) a significant over-abundance of landslides in the hanging walls of ruptured thrust faults relative to the footwalls rate are reported (e.g., [4,5]), showing the effect of the dynamics of the fault rupture on the landslide distribution; (2) the greater erosion rate due to precipitations observed after the earthquake [8,10] shows that earthquakes are found to interact non-linearly with precipitations; (3) the site effect, or amplification of the seismic waves due to shear-wave velocity contrast between the landslide material and the stable material [11,12] or topographical particularities like ridges [9]

Summary

Introduction

Earthquake is one of the main triggering factors of landslide [1] and the most damaging trigger of landslides in terms of social cost. The source magnitude controls the area affected by landslides [1] relating the ground motion decay with distance to the epicenter or to the fault plane (e.g., [3]) This generic law is affected by different factors: (1) a significant over-abundance of landslides in the hanging walls of ruptured thrust faults relative to the footwalls rate are reported (e.g., [4,5]), showing the effect of the dynamics of the fault rupture on the landslide distribution; (2) the greater erosion rate due to precipitations observed after the earthquake [8,10] shows that earthquakes are found to interact non-linearly with precipitations;

Methods

Findings

Discussion

Conclusion