SAFER Project - FINAL MEETING Elin Skurtveit & Amir M. Kaynia - NGI Earthquake-induced Landslides Hazard zonation in Campania – application and implementation in ArcGIS SAFER Project - FINAL MEETING Elin Skurtveit & Amir M. Kaynia - NGI

Initial objectives Calibrate a landslide susceptibility model based on topographic and lithological properties of slope and combine it with a deterministic model based on: mechanical parameters of the soil geometrical properties of the slope characteristics of the earthquakes Validate the model through documented case histories and database of historical landslides. Establish a GIS-based methodology to couple landslide model to Shake maps in order to produce real-time slide maps. In cooperation with AMRA and using the shake maps generated in WP2, apply the seismic landslide susceptibility model to a study region in Campania, Italy. Establish a model for pore pressure generation/dissipation under cyclic loading of earthquake and develop computational tool for post-earthquake landslides.

Outline of presentation Empirical Slope Deformation Analysis Verification of models for landslide prediction Implementation of landslide prediction model in ArcGIS Application of ArcGIS model to test site in Campania, Italy

Empirical Slope Deformation Analysis Factor of Safety Why Translational Slide Model? Failures in natural slopes are typically shallow and they have small thickness to length ratios c = soil cohesion h = slab thickness b = slope angle f = internal friction angle of soil g ,gw = unit weight of soil and water n = percentage of saturated slab thickness Yield Acceleration of Slope ay = yield acceleration of the slope (Applied in the direction parallel to slope)

Empirical Slope Deformation Analysis Sliding Displacement Prediction Models California Method (Blake et. al. 2002) The predictive equation developed by Bray and Rathje (1998) is presented in Recommended Procedures for Implementation of DGM Special Publication 117: Guidelines for Analyzing and Mitigating Landslide Hazards in California u = permanent displacement in centimetres D5-95 = Significant duration parameter (time difference between 5% and 95% development of Arias Intensity) kmax = maximum horizontal equivalent loading coefficient Standard error for this equation is 0.35 in log 10-units (Limited number of strong motions used were available) Bray and Rathje (1998)

Empirical model of landslide: 1. Establish Factor of safety against failure (H = depth to sliding, C = soil’s shear strength) 2. Calculate yield acceleration of slope: 3. Calculate slope’s displacement (D5-95 = significant duration, kmax = peak ground acceleration in g):

Verification of model for landslide prediction Four Case histories of observed landslide or large slope displacements were used: Landslide movement during Northridge Earthquake Debris slump caused by Suusamyr Earthquake Yokowatashi landslide during Niigata-Ken Chuetsu earthquake Landslide movement during Coyote Lake Earthquake

Verification of model (cont.) Results of comparisons with case histories of landslides are encouraging and indicate a fairly good performance of the model. The model is also able to explain the upper bound of historical landslides, established by Keefer (1984), as function of distance and earthquake magnitude. This model is being implemented in a GIS for mapping of landslide zones

Application of ArcGIS Model to test site in Campania, Italy Study area – Campania Destra Sele River Basin Available data (provided by AMRA and INGV) Digital elevation model Geology Geotechnical parameters Shake Map Irpinia 1980 earthquake

Earthquake data Peak Ground Acceleration map from the Irpinia 1980 earthquake Provided by INGV

Geology of the Study area Fiorillo & Wilson, 2004

Implementation of landslide prediction model in ArcGIS Raster Calculation and Map Algebra functions. Example: The result of [Inlayer1] + [Inlayer2] / 2 results in an output grid displaying the mean value for every cell. Raster slope map calculated from Digital Elevation Model Cellsize: 40 m x 40 m

Implementation of landslide prediction model in ArcGIS Input raster layers Geology & geotechnical parameters Geometry of slope ArcGIS Raster calculation model for factor of safety and the yield acceleration of the soil

Implementation of landslide prediction model in ArcGIS Calculate slope’s displacement, u: Input raster layers PGA Soil strength / safety factor Magnitude and distance D5-95 = significant duration, kmax = peak ground acceleration in g Raster calculation model for soil displacement

ArcGIS displacement map Slope Displacement in cm

Sliding Displacement Evaluation – Comparison with the Extended Models Reference Saygili and Rathje (2008) Bray and Travasarou (2007) Blake et. al. (2001)* GM Parameters PGA,M PGA,PGV PGA PGA, D5-75 Min Displacement 0 cm Max Displacement 76 cm 78 cm 97cm 171 cm 0 - 5 cm 99.44% 99.41% 99.37% 5 - 15 cm 0.31% 0.32% 0.34% 0.26% 15 - 30 cm 0.11% 0.10% 0.07% 0.12% > 30 cm 0.14% 0.13% 0.18% 0.25% The results from various recent models compare very well with the California Model* ShakeMaps indicate that PGA and PGV values range from around 0.05 to 0.15 g and 5 to 20 cm/s over most of the slopes, respectively. It is observed that the zones corresponding to the sliding displacements greater than 5 cm cover a very small portion (around 0.55%) of the study region. The reasons for low hazard potential are: Slopes have relatively high shear strength Severity of the ground shaking is not strong

Conclusions Verification of slope displacement model for landslide prediction using case histories. Application of landslide prediction model to test site in Italy. Results shows how a GIS-based method can be implemented for near real-time prediction and mapping of landslides. Results from various recent slope deformation models compare very well with the California Model used in this study.