Spatial and temporal management for the probabilistic landslide hazard assessment considering landslide typology

A general methodology for the probabilistic assessment of rotational slide hazard at a regional scale is applied in a test site in the north of Lisbon (Portugal). Landslide susceptibility is assessed using algorithms based on statistical/probabilistic analysis applied over unique-condition terrain units, in a GIS environment. Results of susceptibility predictions are validated by partitioning the landslide data-set using temporal, spatial and random criteria. Prediction-rate curves are used for the quantitative interpretation and classification of the susceptibility map. Integration of triggering information in the modeling procedure is based on the assumption that the same rainfall patterns (quantity/duration), which produced slope instability in the past, will produce the same effects in the future. The landslide hazard is the probability of each pixel to be affected by a slope movement, and results from the coupling between the susceptibility map, predictionrate curve and return periods of critical rainfall events, on a scenario basis. years. Although the relatively small sample, the landslide group can be considered representative from the geomorphological point of view, and can be used for prediction purposes. The landslide areas (mean size, 6,544 m2; total, 137,415 m2) and, particularly, the landslide volume (mean, 14,650 m3; total, 307,653 m3) show the considerable potential economic significance of rotational slides in the test site. In fact, rotational movements have been responsible for damage to property and built structures (mainly roads) in recent years. Figure 1. Geological map of the Fanhões-Trancão test site and spatial distribution of rotational slides. 1. Upper Barremian – Aptian sandstones; 2. Albian – Middle Cenomanian marls and marly limestones; 3. Upper Cenomanian limestones; 4. Upper Cretaceous Volcanic Complex of Lisbon; 5. Paleogene lacustrine limestones; 6. Paleogene conglomerates and sandstones; 7. Quaternary terraces; 8. Alluvial plain; 9. Fault (uncertain dashed); 10. Rotational slides (white, age ≤ 1967; grey, age > 1967).