Considering seismic coefficient distributions within slopes to calculate landslide reactivation probability

Landslides can be reactivated by earthquakes, causing severe damage to intensely urbanised areas. A probability analysis of earthquake-induced landslide reactivation was performed in the intensely urbanised Avcilar-Beylikdu¨zu¨ Peninsula, 35 km west of Istanbul (Turkey), by considering seismic coefficient distributions within slopes instead of attributing a constant seismic coefficient value. Nine rototranslational landslides with lengths ranging from 100 to 1000 m were inventoried; all of the landslides involved heterogeneous soils ascribable to Cenozoic formations and affected intensely urbanised areas that have expanded significantly over the last decade. Sinusoidal functions characterised by different frequencies and initial phases as well as amplitudes of 0.35 g, corresponding to the peak ground acceleration for a return period of 475 years, were considered. Landslide submasses with secondary sliding surfaces were treated by performing a separate stability slope analysis from that implemented for the main sliding surfaces. Sensitivity analyses were carried out by deriving horizontal seismic coefficient distributions within the landslide masses. These took the form of sinusoidal variations, each controlled by an assumed phase and frequency. Moreover, different water pressure distributions within the landside submasses were considered to account for the possible role of increased water pore pressure during rainfall events. Probability maps were obtained by computing the percentage probability of reactivation for each landslide submass taking into account all the considered seismic coefficient distributions. According to the results obtained, about 33 % of the inventoried landslides have a[50 % probability of being reactivated.