Daniela Farrugia

Evaluation of seismic site response in the Maltese archipelago

The investigation of local ground conditions is an important part of seismic hazard assessment (Fäh et al., ). It is now well–established that earthquake ground shaking is not only a function of the earthquake magnitude and epicentral distance, but also of the site conditions, including soft layers in the sub–soil stratification and topographical features. Local geology can greatly alter the seismic waves from earthquakes by amplifying their amplitude, changing the frequency content and increasing the shaking duration during an earthquake (Kramer, ). In fact, several unconsolidated soft sites have suffered significantly greater damage than rock sites. One case was the  Michoacán earthquake which showed low peak ground acceleration near the epicenter, yet caused severe damage in Mexico City, which is found more than  km away and is characterized by soft shallow sediments (Campillo et al., ). The main parameters responsible for such effects are the shear– wave velocity (VS) structure and thickness of the sedimentary cover, the impedance contrast between the soft sediments and the underlying bedrock as well as the geometry of their interface (Parolai et al.,). Knowledge of the VS structure and/or the resonance frequency of soft soil layers is of utmost importance for the prevention or mitigation of earthquake disasters (Arai and Tokimatsu, ). Such information should contribute to earthquake–hazard mitiga-