Site characteristics and shear wave velocity structure of Bangkok Basin, Central Thailand

Abstract

PreviousNext You have accessSymposium on the Application of Geophysics to Engineering and Environmental Problems 2021Site characteristics and shear wave velocity structure of Bangkok Basin, Central ThailandAuthors: Passakorn PananontKoichi HayashiPassakorn PananontKasetsart UniversitySearch for more papers by this author and Koichi HayashiGeometrics Inc.Search for more papers by this authorhttps://doi.org/10.4133/sageep.33-008 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Bangkok and vicinity, the largest city in Thailand is located in the Lower Central Plain of Thailand in a region characterized by thick Quaternary basin fills. This area has been affected by distant, moderate to large earthquakes in the past which caused damages to the buildings. In this study, three component microtremor measurements and shallow to deep shear wave velocity (VS) measurements have been performed in the Bangkok Basin and vicinity. Three component microtremor measurements (HVSR, horizontal to vertical spectra ratio) were carried out at 115 sites. The result suggests that the short period horizontal ground response in the Bangkok Basin ranges between 0.31 – 1.07 sec. The study also suggests that the long period horizontal ground response ranges between 1.18 – 5.99 sec. The Vs30 (average VS to a depth of 30 m) deduced from the combined active and passive surface wave methods for 206 sites in the study area indicates that the shallow sediments in Bangkok and vicinity have relatively low Vs30: 86-207 m/s, which are classified as the soil type Class E and Class D based on the NEHRP soil-type classification. Deep Vs measurements have been performed at 26 sites in the Bangkok Basin and vicinity by a two-station spatial autocorrelation method (2ST-SPAC) using long-period accelerometers. Receiver separation varied from 5 to 2,100m and maximum separation (array size) varied from 1,000 to 2,100 m. A spatial autocorrelation was used for calculating phase velocity and clear dispersion curves were obtained in frequency range from about 0.3 to 10 Hz. Minimum frequency ranged from 0.32 to 0.48 Hz. An inversion consisting of a non-linear least squares method and a Genetic Algorithm was used to estimate Vs profiles from the dispersion curves to a depth of about 1,000 to 2,500m depending on the sites. The Vs profiles obtained by the inversion can be summarized as follows. A low velocity layer with Vs lower than 500 m/s exists between depths of 0 to 200 m at all sites. Intermediate bedrock with Vs of 1,000-1,500 m/s exists between depths of 240 to 1,000 m. The deepest bedrock with Vs higher than 2,000 m/s seems to exist at a depth of at least 1,000 m. The character of seismic ambient noise affect the quality of the acquired data very strongly and can produce poor result, especially at the low frequency region (less than 1 Hz) and results in unresolvable Vs model at the deeper part of the basin. Therefore the data acquisition in the big cities such as Bangkok must be carefully planned along with proper logistic and security to obtain the optimal result. Keywords: dispersion, inversion, algorithm, shallow, low frequencyPermalink: https://doi.org/10.4133/sageep.33-008FiguresReferencesRelatedDetails Symposium on the Application of Geophysics to Engineering and Environmental Problems 2021ISSN (online):1554-8015Copyright: 2021 Pages: 349 publication data© 2021 Published in electronic format with permission by the Society of Exploration Geophysicists and Environment and Engineering Geophysical SocietyPublisher:Environmental & Engineering Geophysical Society HistoryPublished: 11 Jun 2021 CITATION INFORMATION Passakorn Pananont and Koichi Hayashi, (2021), "Site characteristics and shear wave velocity structure of Bangkok Basin, Central Thailand," Symposium on the Application of Geophysics to Engineering and Environmental Problems Proceedings : 14-14. https://doi.org/10.4133/sageep.33-008 Plain-Language Summary Keywordsdispersioninversionalgorithmshallowlow frequencyPDF DownloadLoading ...