Investigation of Surface Geology and Intensity Variability in the Palermo, Italy, Urban Area after the 6 September 2002 Earthquake

Abstract

For the first time, a high-density macroseismic survey has been carried out in the city of Palermo, Italy, after the 6 September 2002, M w 5.9 earthquake. The aim was to investigate the spatial relationships and correlations between intensity data and surface geology. A very dense database has been created to store a large amount of macroseismic, stratigraphic, and geotechnical information. A Geographic Information Systems (GIS) tool, called City-GIS, enables data processing by instruments and research keys devoted to seismic hazard. The results show the feasibility of such procedures, especially for large cities where the surface geology critically influences the ground motion. Our analysis, made on the basis of more than 2000 intensity observations scattered in the Palermo urban area, demonstrates the role of the variable geology in the variability of shaking. Significant variations of intensity are related to the geometry of the geologic formations present in the area. Intensities increase by about one intensity class inside those city sectors where the stratigraphic succession is characterized by a thin layer of calcarenites overlying very thick layers of silty clayey sands. Major amplification of up to two classes occurs in alluvial deposits in the southeastern part of Palermo, as expected. These results extend our knowledge of the seismic response in the outskirts of Palermo, which until now, was limited to the city center.

Effect of Local Geology on Ground Motion in the City of Palermo, Italy, as Inferred from Aftershocks of the 6 September 2002 Mw 5.9 Earthquake

“…In their simulation, the peak ground acceleration (PGA) value at the rock site was found to be lower than 0.01g for the vertical component and 30% higher for the horizontal component, consistently with the lack of triggering at the analog accelerometric stations around Palermo. PGA of the simulated horizontal ground motion for the soft-soil stations attained 0.04g, on the average, that is consistent with MCS intensity V-VI documented for Palermo (Giammarinaro et al, 2005). Figure 7b shows the acceleration response spectra for three different simulations of the M w 5.9 mainschock at the three sites.…”

The catastrophic 1883 earthquake at the island of Ischia (southern Italy): macroseismic data and the role of geological conditions

“…Moreover, based on macroseismic data, several studies have proposed seismic zoning of some cities, comparing data of historical and recent earthquakes with surface geology and active tectonic structures. These studies show that severe damage generally occurs on soft substrata (Esposito et al 1992;Tertulliani and Riguzzi 1995;Fah et al 1997;Sousa and Oliveira 1997;Cifelli et al 2000;Boccaletti et al 2001;Giammarino et al 2005). However, earthquakes of about intensity that are one degree higher is normally expected for soft soil sites than for rocky ones (e.g.…”

3D City Models as a Visual Support Tool for the Analysis of Buildings Seismic Vulnerability: The Case of Lisbon

“…A slope map, based on the digital terrain model, shows that only 5% of the total area of the city has slopes higher than 10% (Teves-Costa et al 2011). Taking into account that the local conditions (soil type and topography) can modify the characteristics of the seismic ground shaking (Borcherdt 1970;Idriss 1990), thus affecting the observed macroseismic intensity (Giammarinaro et al 2005;Fritsche et al 2009;Navarro et al 2009), an aggravating factor was introduced in the mean damage degree equation used in RISK-UE (Milutinovic and Trendafiloski 2003). This aggravating factor, presented in Table 6, varies from -0.25 to ?1.5, depending on the earthquake source, taking into account the combined effect of the topography and the geology (TevesCosta et al 2011).…”