Landslide size matters: A new data-driven, spatial prototype

Luigi Lombardo,Hakan Tanyas,Raphaël Huser,Fausto Guzzetti,Daniela Castro-Camilo

doi:10.1016/j.enggeo.2021.106288

Abstract

The standard definition of landslide hazard requires the estimation of where, when (or how frequently) and how large a given landslide event may be. The geoscientific community involved in statistical models has addressed the component pertaining to how large a landslide event may be by introducing the concept of landslide-event magnitude scale. This scale, which depends on the planimetric area of the given population of landslides, in analogy to the earthquake magnitude, has been expressed with a single value per landslide event. As a result, the geographic or spatially-distributed estimation of how large a population of landslide may be when considered at the slope scale, has been disregarded in statistically-based landslide hazard studies. Conversely, the estimation of the landslide extent has been commonly part of physically-based applications, though their implementation is often limited to very small regions.In this work, we initially present a review of methods developed for landslide hazard assessment since its first conception decades ago. Subsequently, we introduce for the first time a statistically-based model able to estimate the planimetric area of landslides aggregated per slope units. More specifically, we implemented a Bayesian version of a Generalized Additive Model where the maximum landslide size per slope unit and the sum of all landslide sizes per slope unit are predicted via a Log-Gaussian model. These “max” and “sum” models capture the spatial distribution of (aggregated) landslide sizes. We tested these models on a global dataset expressing the distribution of co-seismic landslides due to 24 earthquakes across the globe. The two models we present are both evaluated on a suite of performance diagnostics that suggest our models suitably predict the aggregated landslide extent per slope unit. In addition to a complex procedure involving variable selection and a spatial uncertainty estimation, we built our model over slopes where landslides triggered in response to seismic shaking, and simulated the expected failing surface over slopes where the landslides did not occur in the past.What we achieved is the first statistically-based model in the literature able to provide information about the extent of the failed surface across a given landscape. This information is vital in landslide hazard studies and should be combined with the estimation of landslide occurrence locations. This could ensure that governmental and territorial agencies have a complete probabilistic overview of how a population of landslides could behave in response to a specific trigger. The predictive models we present are currently valid only for the 25 cases we tested. Statistically estimating landslide extents is still at its infancy stage. Many more applications should be successfully validated before considering such models in an operational way. For instance, the validity of our models should still be verified at the regional or catchment scale, as much as it needs to be tested for different landslide types and triggers. However, we envision that this new spatial predictive paradigm could be a breakthrough in the literature and, in time, could even become part of official landslide risk assessment protocols.

Highlights

Landslides are common in the mountains, in the hills, and along high costs, where they can pose serious threats to the population, public and private properties, and the economy (Kennedy et al, 2015; Petley, 2012; Daniell et al, 2017; Broeckx et al, 2019)
We exploit the information on the geographical location and planimetric area of 319,086 landslides shown in 25 earthquake-induced landslides (EQILs) inventories available from the global database collated by Schmitt et al (2017) and Tanyaset al. (2017)—currently the largest and most comprehensive repository of information on seismically-triggered slope failures, globally (Fan et al, 2019)—together with spatial morphometric and environmental variables in the areas covered by the 25 EQIL inventories, and on the seismic properties of the triggering earthquakes
We provide an overview of the inferred covariate effects and conclude presenting a graphical translation of the model's output into map form

Summary

Introduction

Landslides are common in the mountains, in the hills, and along high costs, where they can pose serious threats to the population, public and private properties, and the economy (Kennedy et al, 2015; Petley, 2012; Daniell et al, 2017; Broeckx et al, 2019). A problem with this definition is that, in contrast to other natural hazards—including, e.g., earthquakes (Wood and Neumann, 1931; Gutenberg and Richter, 1936), volcanic eruptions (Newhall and Self, 1982), hurricanes (Saffir, 1973; Simpson, 1974), floods (Buchanan and Somers, 1976)—no unique measure or scale for landslide magnitude exists (Hungr, 1997a; Malamud et al, 2004b; Guzzetti, 2005).

Results

Discussion

Conclusion