Engineering properties and dynamic behavior of caliche deposits in a seismically active region in southern Turkey

Despite the epcientral distance of 40 km significant structural damage was observed during the Adana–Ceyhan earthquake (Mw = 6.2) of 27 June 1998 in the countryside where mostly low-rise (1–2 storey) buildings are founded on caliche deposits. However, the observed damage was not uniform in that similar buildings located on other caliche sites were only slightly damaged. This study evaluates the engineering and dynamic behavior of the caliche deposits in an effort to explain the observed variation in damage. Horizontal-to-vertical spectral ratios were obtained from both microtremor measurements and strong motion records of aftershocks. Furthermore, ground amplification was modeled using one-dimensional site response analysis based on the soil profiles that were obtained from previously available geotechnical and geophysical data. The results compared with the observed damage distribution show that significant amplification does not occur on most of the caliche deposits for frequencies up to 10 Hz. Moreover, the largest amplification factor of about 5 was found at frequency of 7.5 Hz in Kılıçlı village in which mostly low-rise (1–2 storey) buildings are located. Results of 1-D linear site response analyses suggest that 1 or 2 m thick hardpan lying on top has no significant effect on soil amplification other than a slight shift in fundamental frequency. Amplification is most significantly influenced by the thickness of the softpan.