Abstract
In this study, we aimed to explore the S-wave velocity structure of shallow soils using microtremors in order to estimate site responses in Tekirdag and surrounding areas (NW Turkey). We collected microtremor array data at 44 sites in Tekirdag, Marmara Ereglisi, Corlu, and Muratlı. The phase velocities of Rayleigh waves were estimated from the microtremor data using a Spatial Autocorrelation method. Then, we applied a hybrid genetic simulated annealing algorithm to obtain a 1D S-wave velocity structure at each site. Comparison between the horizontal-to-vertical ratio of microtremors and computed ellipticities of the fundamental mode Rayleigh waves showed good agreement with validation models. The depth of the engineering bedrock changed from 20 to 50 m in the Tekirdag city center and along the coastline with a velocity range of 700–930 m/s, and it ranged between 10 and 65 m in Marmara Ereglisi. The average S-wave velocity of the engineering bedrock was 780 m/s in the region. We obtained average S-wave velocities in the upper 30 m to compare site amplifications. Empirical relationships between the AVs30, the site amplifications, and also average topographic slopes were established for use in future site effects microzonation studies in the region.
Highlights
Destructive earthquakes in the past have shown that local site conditions have major effects on ground shaking
The importance of site effect studies has been more widely recognized since the 1999 Kocaeli Earthquake (Mw 7.4) in Marmara Region (NW Turkey), especially in the Istanbul megacity
AVs30 and site amplification relationship We examined the relationship between the amplification factor and AVs30
Summary
Destructive earthquakes in the past have shown that local site conditions have major effects on ground shaking. Estimation of Vs profiles with direct methods, like borehole and drilling, requires geophysical or laboratory testing and imposes significant cost and time constraints. There are simple, economical, and rapid indirect methods to evaluate Vs profiles, like spectral ratios of horizontal-to-vertical components (H/V). The importance of site effect studies has been more widely recognized since the 1999 Kocaeli Earthquake (Mw 7.4) in Marmara Region (NW Turkey), especially in the Istanbul megacity. The Avcilar district of Istanbul in the western part of the city is ~150 km far from the Kocaeli earthquake epicenter, many buildings collapsed during the earthquake. This demonstrates that even places distance from an earthquake source cannot be considered safe. This demonstrates that even places distance from an earthquake source cannot be considered safe. Ozel et al (2002, 2004), Kudo et al (2002), Ergin et al (2004), Karagoz et al Earth, Planets and Space (2015) 67:176
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