A Monte-Carlo based microzonation model for application in seismic hazard studies

Abstract

During a strong earthquake, the local geological and geotechnical conditions can significantly alter the earthquake shaking in terms of amplitude, frequency content, and duration, a phenomenon often referred to as the site effect. In the past decades, the shear-wave velocity of the top 30 m (V_s30) and the fundamental period of vibration (T₀) were established as indicators for the seismic site effects. To improve understanding of subsurface ground conditions and their spatial variation in the Saguenay region, Canada, a Monte-Carlo based approach is proposed for V_s30 and T₀ modelling. First, a detailed probabilistic 3D geological model was developed considering three soil types: glacial till and postglacial fine and coarse sediments. The study area was modelled with 3D 75x75x2 m grid cells using sequential indicator simulation assigning probability of occurrence of each of the soil types to each cell. In parallel, a comprehensive Vs database was created based on invasive geotechnical measurements. Interval Vs probability distributions were determined for each soil type at each 2m depth. Monte-Carlo (MC) simulations were conducted considering Vs as the random variable. The resulting probability values were used to create V_s30 and T₀ maps and associated uncertainties. These results demonstrate the capacity of the proposed MC approach to incorporate the variability of the subsurface conditions in the seismic hazard assessment process.