Microtremor Measurements for the Microzonation of Dinar

Abstract

Ð The geotechnical site conditions in Dinar town located in western Turkey were investigated after the 1995 Dinar earthquake based on borings, in situ penetration tests, seismic wave velocity measurements, and microtremor records. The variation of damage distribution within the town was evaluated with respect to 23 district damage ratios calculated, based on the detailed damage survey conducted by the General Directorate of Disaster Aairs. Site ampli®cations were estimated from microtremor spectral ratios and microzonation was performed using a GIS methodology. The results of in situ penetration tests and seismic wave velocity measurements as well as the damage distribution were compared with the ampli®cation zonation obtained from microtremor records. The results indicate the applicability of microtremor spectral ratios for assessing the local site conditions and site ampli®cations.

Contributions of Basin-edge-induced Surface Waves to Site Effect in the Dinar Basin, Southwestern Turkey

“…Extensive investigations were performed before and after the earthquake to determine the geological and geotechnical properties of the Dinar basin. These include numerous 30 m deep boreholes opened in different parts of the town (ERKEN et al, 1999;ANSAL et al, 2001;BAKIR et al, 2002). Comprehensive seismic refraction surveys were also performed within the town to provide shear-wave velocity profiles of subsurface soil to 20 m depth (TURKER et al, 1996).…”

“…SUCUOGLU et al (2003) showed that at most periods, the response spectrum from the Dinar accelerogram is smaller than the design response spectrum specified for zone 1 in the Turkish seismic design code. 90 people died and about 40% of the total buildings collapsed or were heavily damaged during the Dinar earthquake (ANSAL et al, 2001). The majority of housing and other settlements are located in the Dinar basin, and some settlements are located in the mountainous area.…”

“…The Dinar earthquake occurred on the Dinar fault which borders the eastern edge of Dinar basin ( Figure 2). While the structures located within the Dinar basin were heavily damaged, the structures located on the relatively strong hard rock were not damaged or very lightly damaged during the earthquake (DURUKAL et al, 1998;ANSAL et al, 2001). In previous studies, a relation between the damaged properties and the site characteristics in Dinar has been sought (KAYABALI, 1997;ANSAL et al, 2001;BAKIR et al, 2002).…”

“…While the structures located within the Dinar basin were heavily damaged, the structures located on the relatively strong hard rock were not damaged or very lightly damaged during the earthquake (DURUKAL et al, 1998;ANSAL et al, 2001). In previous studies, a relation between the damaged properties and the site characteristics in Dinar has been sought (KAYABALI, 1997;ANSAL et al, 2001;BAKIR et al, 2002). KAYABALI (1997) investigated the influence of the soil behavior on the damage to buildings caused by the earthquake, using one-dimensional modeling, and his results show that the fundamental soil periods lie between 1.3 and 2.7 sec., for basin thicknesses ranging between 150 to 250 m. Since these periods are notably high and far beyond the natural periods of damaged buildings (0.4-0.6 sec for 4-6-story buildings which showed maximum damage), the heavy damage in Dinar was related to poor construction quality, the short distance to the epicenter and the long duration of the earthquake.…”

“…KAYABALI (1997) investigated the influence of the soil behavior on the damage to buildings caused by the earthquake, using one-dimensional modeling, and his results show that the fundamental soil periods lie between 1.3 and 2.7 sec., for basin thicknesses ranging between 150 to 250 m. Since these periods are notably high and far beyond the natural periods of damaged buildings (0.4-0.6 sec for 4-6-story buildings which showed maximum damage), the heavy damage in Dinar was related to poor construction quality, the short distance to the epicenter and the long duration of the earthquake. ANSAL et al (2001) computed the fundamental soil periods for Dinar basin between 0.14 and 0.93 sec from microtremor measurements. They noted that both the importance of site effect and poor construction quality became important in the major damage in Dinar.…”