Soil and sediment quality and composition as factors in the distribution of damage at the December 26, 2003, Bam area earthquake in SE Iran (M s = 6.6)

Background, aim, and scope The rapid growth of the world's population over the past few decades has led to a concentration of people, buildings, and infrastructure in urban areas. The tendency of urban areas to develop in sedimentary valleys has increased their vulnerability to earthquakes due to the presence of soft soil and sediment. Several earthquakes have clearly demonstrated that local soil and sediment conditions can have a significant influence on earthquake-induced ground motion and damage pattern, respectively. Many studies confirm the relationship between site effect and ground motion (Borcherdt in Bull Seismol Soc Am 60:29-61, 1970; Bouckovalas et al. in Geotech Geolog Eng (Historical Archive) 14(2):111-128, 1996; Fäh et al. in Seismology 1:87-10, 1997; Atakan et al. in Nat Hazards 15(2-3):139-164, 1997; Christaras et al. in Geodynamics 26(2-4):393-411, 1998; Raptakis et al. in Bull Earthquake Eng 2(3):285-301, 2004a; Raptakis et al. in Soil Dyn Earthq Eng 25:871-887, 2005; Marka et al. in Pure Appl Geophys 158:2349-2367, 2001; Marka et al. in Soil Dyn Earthq Eng 25(4):303-315, 2005; Importa et al. in Seismology 9(2):191-210, 2005; Tyagunov et al. in Nat Hazards 38:199-214, 2006; Lombardo et al. in Nat Hazards 38:339-354, 2006; Rayhani et al. in Geotech Geol Eng 21(1):91-100, 2008). In order to classify the suitability of the soil and subsurface sediment units for urban planning and compare their mechanical behavior with the non-uniform damage observed in the 2003 earthquake, we performed some geotechnical and geophysical analyses of soil and sediment samples collected from different locations in Bam City. Methodology Geophysical and geotechnical properties, such as grain size distribution, sorting, plasticity, Poison's ratio, shear strength, compression index, permeability, and P and S wave velocities in soil and subsurface sediments, were measured. Maps (in GIS environment) and cross-sections were prepared for the study area. Results According to our observations, a great number of buildings were damaged in areas of the city where silty and clayey soils dominate, presenting very low permeability, low wave velocity together with high plasticity, and compressibility. In the study area, we recognized eight sediment types. Shear wave propagation velocities allowed for the identification of four seismic layers referred to as the surface layer, second layer, and third layer and seismic bedrock. We found that the damages observed in the Bam area wer