Simulating Earthquake Scenarios in the European Project LESSLOSS: The Case of Lisbon

Abstract

Within the framework of the European LESSLOSS Project “Risk Mitigation for Earthquakes and Landslides”, finite-fault seismological models have been proposed for the computation of earthquake scenarios for three urban areas: Istanbul (Turkey), Lisbon (Portugal) and Thessaloniki (Greece). For each case study, ground motion scenarios were developed for the two most probable events with different return periods (generally 50 and 500 years), locations and magnitudes that were derived from historical and geological data. The ground motion simulations were performed in the frequency band of engineering interest (0.5-20 Hz) by two numerical finite-fault methods: a hybrid deterministic-stochastic method, DSM, used for all of the cases investigated, and a non-stationary stochastic finite-fault simulation method, RSSIM, applied only in the case of Lisbon. In the present study, the results with respect to bedrock and surface are presented in terms of peak ground acceleration (PGA) for the city of Lisbon and the surrounding area, using earthquake scenarios from the onshore source area of the Lower Tagus Valley, and from the offshore source area of the Marques de Pombal fault, which is one of the possible sources of the 1755 Lisbon earthquake. Site effects are evaluated by means of a properly designed equivalent stochastic non-linear one-dimensional ground response analyses of stratified soil profile units. The requirements of the users (e.g., engineers, local administrators) constrain the choice of the scenario that can be adopted as input for disaster scenario predictions and loss modelling; in the case of Lisbon, the maximum values of shaking were assumed as the criteria for the reference scenarios.