Iranian Journal of Geophysics

Iranian Journal of Geophysics

Site-specific response spectrum estimation for type III soil in Kish island

Articles in Press

Document Type : Research Article

Authors
Shima Taheri 1
Majid Mahood 2
1 Assistant Professor, Department of Civil Engineering, Payame Noor University, Tehran, Iran
2 Assistant Professor, Earthquake Prediction Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
10.30499/ijg.2025.545152.1724
Abstract
Given the critical importance of structures such as power plants, dams, bridges, and industrial facilities, it is essential to evaluate their seismic vulnerability and the potential hazards arising from local site conditions, which can significantly amplify seismic risk. With the rapid development of vital infrastructure and construction of high-rise buildings on Kish Island, which is located within the active Zagros folded zone, accurate seismic hazard assessment has become increasingly important. This study investigated the seismicity within a 100 km radius of Kish Island and estimated a site-specific response spectrum, comparing it with the standard spectrum defined in Iranian Code 2800. According to this code, Kish Island is classified as a relatively high-risk seismic zone. The largest recorded earthquake in the region occurred on March 16, 2022, with a magnitude of 6.1 near Kookherd, approximately 70 km northeast of Kish Island, Iran. Ground motion records from two significant earthquakes near Bandar Charak, which were also recorded in Kish, were utilized to estimate the site-specific spectrum. These include the June 15, 2022 (M5.5), and June 25, 2022 (M5.7), events, which occurred at distances of 49 km and 31 km from Kish, respectively. Records from the Bam earthquake were also considered because of the similar site conditions. The results indicate that the site-specific response spectrum exceeds the standard values for periods up to 0.5 s and remains above the minimum of the standard spectrum across all periods. This spectrum, which accounts for regional tectonics and site effects, is recommended as a reliable tool for designing critical and high-rise structures. It was also applied in the analysis of a building currently under construction in Kish Island. In the context of site-specific response spectra for Kish Island, characterized by Type III soil (medium to soft soils with shear wave velocities typically ranging between 175 m/s and 375 m/s according to Iranian Code 2800), the impact of soil-structure interaction (SSI) on the seismic behavior of high-rise buildings is critical. Type III soil, commonly found in coastal regions such as Kish Island due to sandy and calcareous deposits overlying clay layers, tends to amplify ground motions, resulting in increased structural demands compared to stiffer soils. SSI in Type III soil environments alters the dynamic characteristics of tall buildings by lengthening their natural period and increasing the damping owing to soil flexibility and radiation damping effects. Future research should refine site-specific response spectra through probabilistic assessments of soil-structure interaction (SSI) to better align with the requirements of Iranian Code 2800.
Keywords
Soil type
site-specific response spectrum
site effect
seismic hazard
Kish island

Subjects

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Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 19 December 2025