Quantitative seismic hazard assessment

We analyze the ingredients required for deterministic wave propagation simulation in order to estimate more accurately ground motion in terms of amplitude, frequency content and duration. Building maps of expected ground motion before a catastrophic event for various scenarios may help design ways to mitigate impacts of ground vibrations as well as fast calibration of these maps once the event occurs. Reconstruction of 3D structures requires collection of information at two different scales: the regional one (a few tens of kilometres) and the local (a few tens of metres to hundreds of metres). Different techniques from permanent to temporary deployments of seismic stations and from active to passive source excitations together with other geophysical and geotechnical investigations will provide the necessary information. Characterisation of possible seismic sources is another challenge and requires careful seismotectonic analysis in the region of interest. Uncertainties may be large provided that one can reproduce wave propagation from these hypothetical spatially extended sources. Frequency content of these simulations is more limited by our knowledge of the medium than by computer resources. In fact, in order to perform such simulations, the geological structure has to be known within a resolution scale of one-tenth of the wavelength. Duration and amplitude are affected by the source mechanism and the mechanical properties of the underground structure. Variability in these ground motion estimations should be appreciated and key parameters identified. Designing approaches to calibrate these simulations with recorded data as well as necessary links with the probabilistic approach should be addressed in the future.