Advance in seismic site response : usual practices and innovative methods

Abstract

Amplitudes and frequency content of the seismic ground motion generated by an earthquake and recorded at a specific location depends on the characteristics of the source, the path from the source to the site and the local geologic conditions. The local site seismic response is produced by multiple physical phenomena (i.e., reflection, diffraction, focusing, resonance effects, non-linear soil behavior) that can amplify or decrease amplitudes of seismic waves near to the surface causing high variability in the observed ground motions. In particular, vertical discontinuities and abrupt changes in the velocity profile, or lateral heterogeneities such as faults and/or stratigraphic contacts can have a strong impact. A correct and quantitative assessment of site effects is required for both the interpretation of observed waveforms and the reliable prediction of resultant ground motions (e.g., computation of specific earthquake scenarios). In addition, the extent and distribution of building damage due to moderate and large earthquakes in densely populated areas are a result of the combined effect of local site response and the dynamic properties of man-made structures. The quantification of ground motion amplification are therefore of primary interest for seismologists and engineers in order to reduce associated risks.

Recent advances in engineering seismology research resulted in improvements in the study of seismic site response both from the theoretical and experimental points of view. For example, new numerical modelling techniques have become available, which account for non-linear soil behavior. Growing seismic networks allow for the more advanced site response estimates compared to the past as well (e.g. the development of more reliable ground motion prediction equations). [excerpt]