On the use of physics-based ground motion simulations for seismic hazard and risk assessments

Seminars organized by the DICA Scientific Commission
VI cycle – Academic Year 2018/19

Chiara Smerzini

Earthquake ground motion models are a key ingredient in seismic hazard and risk studies, both within probabilistic and deterministic frameworks, providing estimates of probability distribution of ground motion intensity measures as a function of explanatory variables, such as magnitude, distance and site conditions. A variety of methods has been proposed to this purpose, ranging from empirical Ground Motion Prediction Equations (GMPEs), typically calibrated on instrumental observations from past earthquakes, up to complex Physics-Based earthquake ground motion Simulations (PBS), based on the numerical approximation of the elastodynamics equation.
GMPEs are well consolidated in engineering practice due to their simplicity but suffer from some intrinsic drawbacks, which range from the scarcity of data in the near-source region of severe earthquakes to the inability to account for region- and site-specific geologic conditions and for spatial variability of ground motion. On the other hand, PBS provide as output ground motion time histories reflecting the physics of the whole seismic wave propagation problem from the earthquake source to the propagation path and local site response. In recent years, with the tremendous progress in computational resources, PBS have emerged as a promising tool to construct reliable ground shaking scenarios and, hence, to complement effectively empirical predictions.
In this context, the seminar provides an overview of recent advances conducted on the development of an open-source numerical code for PBS –SPEED: SPectral Element in Elastodynamics with Discontinuous Galerkin (http://speed.mox.polimi.it/) – and on its application to seismic hazard and risk assessment studies, with reference to different projects funded by both private and public institutions. Selected case studies are discussed to provide insights into crucial aspects in the generation and use of PBS for engineering applications, namely: the validation of broadband synthetic ground motion against recordings, the incorporation of ground shaking scenarios in both seismic hazard and risk assessment studies for large urban areas and the use of synthetic time histories in seismic analyses of structures.