Assessment of site specific earthquake hazards in urban areas. A case study: the town of Afula, Israel, and neighbouring settlements

Quantifying the seismic hazard in terms of acceleration response spectrum, we present a methodology in which dense measurements of the horizontal-to-vertical (HN) spectral ratios from ambient noise are used to assess the site-specific uniform seismic hazard across urban areas. This process of hazard assessment involves: detailed mapping of the fundamental and other natural frequencies and amplitudes of HN spectral ratios; compiling geological, geophysical and borehole data and integrating it with HN observations to develop models for the subsurface of many sites across the study area. The subsurface model serves as input for computing the expected Uniform Hazard Site-Specific Acceleration Response Spectra at the investigated sites. The final stage is generalizing the hazard by mapping zones that feature similar seismic hazard functions. This paper demonstrates the methodology and the applied procedures by presenting the studies performed in the town of Afula in Israel. The study area is slightly extended to include close-by settlements around the town.