Abstract
Earthquake-induced landslides may be responsible for more damages and losses than the seismic shaking itself. Along with co-seismic failures, earthquakes may also contribute to the progressive degradation of slope properties and the development of large deformation in slopes that could fail under subsequent loadings (rainfall or earthquakes). Such landslides are called reactivated landslides.
The proposed PhD project aims at better understanding the conditions leading to seismic reactivation of existing landslides. It will also quantify co-seismic and post-seismic displacements, the latter being due to shear strength reduction and modifications of hydrogeological conditions.
Earthquake-induced displacements are conventionally assessed using analytical simplified methods (Martino, 2015):
- the permanent displacements method introduced by Newmark (1965). Landslide displacements in a rigid block sliding on an inclined plane are calculated each time the seismic acceleration is larger than the critical acceleration;
- the empirical laws derived from statistical analyses of Newmark displacements. Such methods produce Newmark displacements estimates as a function of Arias intensity and critical acceleration.
These methods are commonly applied at regional scale using Geographical Information Systems (GIS). Based on digital elevation maps, geotechnical and seismological maps and empirical laws, they provide co-seismic displacement estimates for each pixel. Although these methods are widely used, they are characterized by poor spatial resolution.
To overcome these simplifications and resulting limitations, earthquake-induced displacements are also assessed at local scale using Newmark displacement method and numerical simulations in time domain sometimes leading to very different results (Lenti and Martino, 2012 and 2013).
The PhD project therefore mainly aims at:
1- defining conditions requiring 2D numerical simulations. Indeed, Newmark method may provide a wrong estimate of landslide displacements, particularly in steep slopes, probably due to the development of surface waves. According to Meza-Fajardo et al. (2019) surface waves may represent the major contribution to seismic response of soils in sedimentary basins. Unrevealing the role of surface waves in the context of earthquake-induced landslides will be one of the challenges of the PhD.
2- deriving correlations between seismic parameters and seismic slope response in terms of site effects and co-seismic displacements.
3- providing correcting factors to 1D analytical assessments of displacements in GIS in order to better quantify landslide susceptibility at regional scale.
Case study
To characterize landslide susceptibility at regional scale, various geomorphological and geological conditions must be selected. Slope profiles representative of landslides south of Port-au-Prince (Haïti) will be selected as a case study. In 2010, HaÏti was hit by a very strong earthquake that triggered many 1st time failure and reactivated landslides (Gorum et al., 2013). It is therefore a good candidate for this PhD project. Data will be made available thanks to a collaboration between IFSTTAR and Liege University. A 3D global numerical model of the region will be designed to study the impact of structural features on the seismic response of slopes. Refined 2D and 3D numerical models will also be built to study the seismic response of slopes (landslides, locally influenced by liquefaction phenomena) at local scale. Modifications of geometrical and geological parameters of slopes will help extrapolating the main findings of the research work.
Requirements
Highly motivated candidates with a strong background in soil and rock mechanics and numerical modeling applied to landslide hazard assessment are encouraged to apply. Experience in GIS would be a plus. Candidates must be proficient in English and have the ability to promote their research in scientific papers and in international conferences.
Références
Bird J.J. et Bommer J.J. (2004). Earthquake losses due to ground failure. Engineering Geology, 75 (2), p. 147-179. .
Gorum T. et al. (2013). Complex rupture mechanism and topography control symmetry of mass-wasting pattern, 2010 Haiti earthquake. Geomorphology, 184, pp. 127-138
Keefer D.K. (1984). Landslides caused by earthquakes. Bulletin of the seismological society of America, 95, p. 406-421.
Lenti, L., et Martino, S. (2012). The interaction of seismic waves with step-like slopes and its influence on landslide movements. Engineering Geology, 126, 19–36.
Lenti, L., et Martino, S. (2013). A parametric numerical study of the interaction between seismic waves and landslides for the evaluation of the susceptibility to seismically induced displacements. BSSA, 103(1), 33–56.
Martino S. (2015). Earthquake-Induced Reactivation of Landslides: Recent Advances and Future Perspectives. Natural Hazards. Earthquakes and Their Impact on Society, doi: 10.1007/978-3-319-21753-6_10
Martino, S. et Scarascia Mugnozza, G. (2005). The role of the seismic trigger in the Calitri landslide (Italy): Historical reconstruction and dynamic analysis. Soil Dynamics and Earthquake Engineering, 25, 933–950.
Massey C. et al. (2018). Landslides Triggered by the 14 November 2016 Mw 7.8 Kaikōura Earthquake, New Zealand. Bulletin of the Seismological Society of America ; 108 (3B): 1630–1648. doi: https://doi.org/10.1785/0120170305
Meza-Fajardo K et al. (2019). Surface wave quantification in a highly heterogeneous alluvial basin: Case study of the Fosso di Vallerano valley, Rome, Italy. Soil Dynamics and Earthquake Engineering 120 (2019) 292–300. https://doi.org/10.1016/j.soildyn.2019.02.008. |