Seismic Site Response, Analysis and Characterization of Major Cities in UAE

Abstract

United Arab Emirates (UAE) has experienced significant economic growth in recent years. The accelerated schedule driven projects are compelling designers to use values of seismic hazard (ground motion) that are either significantly conservative or unreliable. Moreover, not all estimates of a seismic hazard analysis such as mapped spectral accelerations, representative hazard spectra, and deaggregation covering all parts of UAE are available. Studies that have attempted to define the seismic hazard in UAE in the past are not in agreement and they either focused on few cities or did not provide all the necessary information. The variations in their results could be attributed to the use of questionable source zonation, activity parameters, and superseded prediction equations. Consequently, designers in UAE have to rely on inaccurate estimate of seismic hazard for the region. Considering substantial development in United Arab Emirates (UAE) and considerable ambiguity faced by the designers in choosing the seismic hazard from disagreeing studies, a new seismic hazard analysis is urgently required. This study is based on the use of homogenized catalogue of various degrees of completeness for temporal distribution of events (Surface magnitudes, Ms), activity parameters based on doubly bounded magnitude-frequency relationships, modified zonation of area sources, and new generation prediction equations. The study aims to provide a comprehensive seismic hazard assessment for all parts of UAE that will provide designers with Hazard curves, values of peak ground accelerations (PGA), mapped spectral accelerations at 0.2s and 1s (S0.2 and S1), Uniform Hazard Spectra (UHS), and deaggregation of seismic hazard. In addition to the estimation of seismic hazard, this study provides estimates of the site amplification for three major cities of UAE (Sharjah, Dubai, and Abu Dhabi). Effect of local site conditions in modifying the seismic waves is well documented in many studies. Site amplification factors as a guideline for typical UAE building sites are not available. As a result, designers in UAE have to rely on factors developed for other regions. These factors are typically obtained by performing equivalent-linear or non-linear site response analysis of sites of known dynamic properties. Site response analyses were performed for different representative subsurface soil models obtained from various sources. Sites were grouped as per the provisions of International Building Code (IBC 2009). The results of this part of the study will provide structural engineers with region specific amplification factors for the development of design spectra instead of relying on factors developed for other regions. The results are generally provided for a return period of 2475 years (2 % probability of excedance in 50 years) in conformance to the provisions given in American codes. The results mapped seismic hazard presented in this study corresponds to rock sites classified as Site Class B according to International Building Code (IBC 2009). The results indicate slightly larger values of seismic hazard compared to some recently published studies. The effect of west coast fault is significant especially at larger return periods and should be taken into account if future studies confirm the presence of a fault along the west coast of UAE and prevalent building codes adopts lower probability of exeedance. The activity in Arabian Craton (background seismicity) contributes mostly to the hazard in most southern part of UAE. The contribution of other sources such as Zargos (Iran) and Oman mountains increases as one move towards the North. The west of the country is dominated by seismicity from Zargos whereas the east by seismicity from Oman mountains. The results of site response analyses (site classes C and D) suggest more amplification in Sharjah than in Dubai and Abu Dhabi because of deep engineering bedrocks in Sharjah. The response spectra of Abu Dhabi and Dubai are scattered as compared to Sharjah because of the variance in soil column depths in Dubai and Abu Dhabi. The amplification factors for Sharjah are in the range of 4 to 6 and for Dubai it is estimated to be around 3 to 4; whereas, the amplification factors for Abu Dhabi ranged from 4 to 8.