Horizontal to vertical spectral ratio (HVSR) measurements in the area damaged by the 2002 Molise, Italy, earthquake

Following the 2002 Molise, Italy, earthquake, we performed a set of horizontal to vertical spectral ratio (HVSR) measurements in the damaged area. We recorded microtremors in all the municipalities reaching VI on the Mercalli-Cancani-Sieberg intensity scale. To calibrate our measurements, we installed accelerometers in two of the most damaged areas. We wanted to study HVSR in an area that is geologically different from areas commonly affected by earthquakes in the Southern Apennines. We also wanted to avoid the damage-attraction effect: after a strong event, most researchers study site amplification just where most of the damage has occurred. They might not consider that different structure vulnerability may mask the true distribution of site amplification. We checked for a possible correlation between observed intensity and the average of the non-flat HVSR measured in each municipality. The significant correlation indicates that site amplification has played a role in the damage pattern observed.