GEOTECHNICAL ISSUES OF THE JUNE 27, 1998 ADANA-CEYHAN EARTHQUAKE

On June 27, 1998, a moderate earthquake measuring 5.9 on the Richter scale struck the alluvial plains of Cukurova at Adana-Ceyhan region of Turkey. The earthquake was felt as far as in Cyprus, Syria, Israel and Jordan. However, the severe shaking was within 150-km radius, and most of the damage was within 40-km radius of the epicenter. The earthquake resulted in 145 deaths, about a thousand injuries and significant damage to more than ten thousand structures. The coincidence of the earthquake epicenter and the fault with a very vulnerable geological surface formation, thick alluvial deposits of Ceyhan River containing loose sand layers, provided for a substantial thickness and areal distribution of liquefied sediments. Consequently, liquefaction associated ground deformations such as lateral spreading, flow failures, ground fissures and extensional cracking, sand boils, ground subsidence and slope failures were widespread. The extent of liquefaction also provided a significant amount of data useful for analyzing the effects of ground liquefaction on the structures typical of rural areas of Turkey. This paper presents and analyses the geotechnical aspects of this earthquake with the main emphasis on the observed liquefaction and associated ground deformations along with the earthquake characteristics. The observed liquefaction mechanisms provide valuable information on the seismic response of the alluvial soils covering most of the Cukurova plains, an important industrialized and agricultural area with more than 2 million inhabitants. A through analysis of case histories reported herein would establish a valuable benchmark for liquefaction susceptibility analyses of the river sedimented soils in the region. Despite the preliminary nature of the study, the observations indicate that liquefaction should be considered in seismic designs in the large areas of Cukurova Plains. Microzonation for Cukurova region is needed to improve risk assessments due to liquefaction and/or ground motion amplification.