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A probabilistic seismic hazard analysis was performed to generate seismic hazard maps for Jamaica. The analysis was then conducted using a standard logic-tree approach that allowed systematically taking into account the model-based (i.e., epistemic) uncertainty and its influence on the computed ground motion parameters. Hazard computations have been performed using a grid of sites with a space of 0.05 degrees. Two different computation methodologies have been adopted: the standard approach based on the definition of appropriate seismogenic sources and the zone-free approach, which overcomes the ambiguities related with the definition of the seismic sources solely reflecting the characteristics of the earthquake catalogue. A comprehensive and updated earthquake catalogue for Jamaica has been compiled for the years 1551-2010 and new empirical relationships amongst magnitudes M W -M S and M W -m b have been developed for the region. Uniform hazard spectra and their uncertainty have been calculated for the horizontal component of ground motion for rock site conditions and five return periods (95, 475, 975, 2,475 and 4,975 years) and spectral accelerations for 34 structural periods ranging from 0 to 3 s, and 5% of critical damping. The spectral accelerations have been calculated to allow the definition of seismic hazard in Jamaica according to the International Building Code 2012. The disaggregation analysis for Kingston Metropolitan Area suggests that the magnitude-distance pair that contributes most to the hazard corresponds to events with M 7.8 and M 7.0 in the Enriquillo Plantain Garden Fault and the Jamaican Faults at a distance of 28 km and 18 km for short and long period structures respectively corresponding to 2,475 years return period. However, for long period structures, a substantial contribution is found for a M 8.2 at a distance of 198 km in the Oriente Fault Zone.

Abstract:A new probabilistic seismic hazard analysis was performed for the city of Bridgetown, Barbados, West Indies. Hazard computations have been performed using the standard Cornell-McGuire approach based on the definition of appropriate seismogenic sources and expected maximum magnitudes, the authors take into consideration the possibility of large subduction interface earthquakes of magnitude 8.0-9.0 beneath the Barbados accretionary prism via application of a characteristic model and slip rates. The analysis has been conducted using a standard logic-tree approach. Uniform hazard spectra have been calculated for the 5% of critical damping and the horizontal component of ground motion for rock site conditions setting 5 return periods (95, 475, 975,2,475 and 4,975 years) and spectral accelerations for 34 structural periods ranging from 0 to 3 s. The disaggregation results suggest that the magnitude-distance pair that dominates the hazard yields M 7.4 and 8.6 and a distance of 42.5 km in the Interface Subduction Zone beneath Barbados for the 475 and 975 years RP (return period), respectively. An event with an M 8.0 at a distance of 107.5 km in the Intraplate Subduction Zone is the second scenario that dominates the hazard for both 475 and 975 years RP.

This book chapter explains the methodology to determine the shear wave velocity V S 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 the city of Port of Spain.

The authors performed single mobile microtremor measurements at 218 sites at KMA (Kingston Metropolitan Area) with the objective of estimating the amplification effects due to the earthquake ground motion on the surface geology. The Fourier transform was applied to the most stationary parts of the triaxial wave motion recordings for each individual site and applied the traditional Nakamura technique, namely, the horizontal to vertical spectral ratio (H/V) to retrieve the predominant shear wave period of vibration of the soil profiles above the bedrock. The results yield predominant long periods of about 3.0-4.0 s in the port area and the waterfront, 1.0-2.0 s in the central part of Kingston, 0.3-1.0 s in Portmore and very stiff soil conditions in the surrounding area of the city. The results coincide fairly well with previous geological studies in the region, geotechnical data in boreholes, gravimetric measurements and strong motion recordings, suggesting a high degree of amplification of ground motion in the whole period range of engineering interest. Additionally, the authors obtained the liquefaction vulnerability factor K g proposed by Nakamura based on the H/V ratio of microtremors. The results suggest that the port area, the waterfront and the Port Royal are highly susceptible to liquefaction. Finally, the authors obtained fundamental periods of vibration based on microtremor measurements on the roof and the basement of four important buildings in the KMA and indicated future lines of research employing ambient noise measurements on structures.