Revealing Hazard: Imagining Exposure and Impact

Chapter 4

and Clevon Ash

the city of Port of Spain.

1. Methods and data

1.1 Array measurement of microtremors

liquefaction

53

Abstract

Estimation of Shear Wave Velocity

Algorithms and the Diffuse Field

Approach on Microtremors Array:

Hazard at Port of Spain, Trinidad

This book chapter explains the methodology to determine the shear wave velocity VS profile employing microtremors array data at Port of Spain, Trinidad, and its implication in the seismic amplification and liquefaction hazard in the city. We divide this study into five sections; firstly, we introduce a description of the spectral autocorrelation method and the genetic algorithm schemes to retrieve the Vs and thickness of soil layers. Secondly, we validate the soil profiles via inspection of the ellipticity pattern at such sites; we also compared the observed horizontal-tovertical spectral ratios (H/V) with the synthetic ones derived by the Diffuse Field Approach and 1D theoretical SH wave amplification functions. Thirdly, we compute the shear wave velocity in the first 30 m obtained from our genetic inversion and compared with the ones estimated by the empirical formulas based on geomorphological conditions. Fourthly, we present a preliminary liquefaction hazard map based on the level of H/V microtremor ratios and the fundamental period of vibration. Finally, we conclude with further recommendations for planning purposes in

Keywords: shear wave velocity, genetic algorithms, fundamental period,

Port of Spain (POS) lies on an alluvial fan deposit and forms a costal aquifer with a high water table comprising poorly sorted gravels, sand, clay, and boulders. The part of today's downtown Port of Spain closest to the sea was once an area of tidal mudflats covered by mangroves which have been reclaimed by anthropological

Profiles Employing Genetic

Implications on Liquefaction

Walter Salazar, Garth Mannette, Kafele Reddock
