The Trinidad and Tobago Microzonation Project: Port of Spain

Abstract

SUMMARYIn this study, we present the results from the microzonation study conducted in Port of Spain (PoS), capital of the Republic of Trinidad & Tobago. A dense grid of single-site recordings was used to determine the fundamental frequency of soil above bedrock, while a grid of 26 array recordings comprised the database for finding the 1-D shear wave velocity, with depth. The resonant frequency was found to range from <1.0 Hz, for the deeper sediments to the south, near the coast, to above 4.0 Hz, on the northern outskirts of the city, closer to the rock formations. The array data processing revealed a shear wave velocity less than 360 m s–1, for the alluvial deposits, whilst for the harder formations, the velocity was at least 1000 m s–1. To validate the results, a parametric investigation, using synthetic seismograms of ambient noise for simplified 1-D models of the PoS basin sediments, was conducted. A 3-D geological model of the basin was developed, by integrating the experimental results with the simulated data. The model suggests a gradual increase, from north to south, in sediment depth down to ∼160 m. In order to understand and explain the variation of the resonance frequency, a review of the historical development of the area, for the past 250 yr, revealed large-scale, non-engineered land reclamation in the 19th and 20th centuries, resulting in areas with anomalously high amplification of seismic motion.