Development of New Design Spectral Accelerations for Bangkok Considering Deep Basin Effects


Abstract eng:
In this study, seismic site effects of Bangkok and the vicinity area focusing on deep basin structures were carefully examined in order to establish the spectral accelerations appropriate for design of structures. Investigation of site characteristics was firstly conducted by microtremor observations to explore shear wave velocity profiles from surface to basement rock. The array microtremor technique employed was the Centerless Circular Array (CCA) method, which could provide long detectable wavelength and deep exploration depth. From 100 sites, shear wave velocities analyzed from the observed dispersion curves exhibit very low value at the uppermost level as the average from the surface to 30-m depth was less than 180 m/s in most sites. Generally, shear wave velocity of the first 100 m were less than 500 m/s. The velocity increased gradually along depth and the underneath layers of stiffer soil exhibit moderate value of about 1000 m/s. The estimated depth of basement rock could be inferred from the level having clear contrasts of shear wave velocity. The velocity at this level generally changes abruptly to be about 2000 m/s or more. The estimated depth of basement rock varies from less than 200 m near the boundary of the basin to 800 m in the central area. In the second part, site response analysis was conducted in order to examine the ground response and to propose seismic microzonation accordingly. The ground motions obtained from Probabilistic Seismic Hazard Assessment were input as rock outcrop acceleration time history and the propagation through the model of soil profiles was analyzed by an equivalent linear analysis. From strong motion database, the input motions were selected and scaled to match response spectra with the Conditional Mean Spectrum (CMS) at 0.2, 0.5, 1.0, 1.5, 2.0 and 3.0 second, for 2475 years return period. Then the average spectral accelerations were used to evaluate the Maximum Credible Earthquake (MCE) design spectrum for each site. The spectral accelerations revealed amplifications in wide range of periods. The results of shear wave velocities and spectral accelerations for neighboring sites were considered for their similarity and the area was sub-divided into three zones consequently. The shapes of the spectral accelerations were the key parameter for seismic microzonation. The proposed zonations were distinct mainly from the amplification at short period of 0.5 second and at long period greater than 1 second.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2141.:
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