High-resolution grid of H/V spectral ratios and spatial variability on microtremors at Port of Spain, Trinidad

Salazar, Walter; Mannette, Garth; Reddock, Kafele; Ash, Clevon

doi:10.1007/s10950-017-9681-1

Cited by 6 publications

(8 citation statements)

References 14 publications

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“…generated by the Diffuse Field Approach (DFA) with the observed ones at the array sites and with empirical formulas to estimate the average shear wave velocity of the upper 30 m (V S 30). We conclude that the H/V ratios yield a genuine shear wave fundamental period of vibration of the soil profiles at POS, and that can be used to validate the high-resolution seismic microzonation map proposed by Salazar et al [1]. The amplification and fundamental period of motion retrieved from the microtremors together with the water table level suggest a high liquefaction potential mainly on the coastal areas.…”

Section: Discussionsupporting

confidence: 74%

“…We plotted two kinds of theoretical SH transfer functions, namely, case (1) up + down amplification with refraction and reflection in bedrock and case (2) only up wave amplification. In both cases the 1-D SH wave amplification replicates the fundamental period of the observed H/V ratios; however, in most of the cases, the overall shape of the H/V ratios differs mainly at long period components for case (1) and for short period components for case (2). It is noticed that a level of amplification yield between three and five yields at the predominant peak.…”

mentioning

confidence: 59%

“…Recent studies suggested a peak ground acceleration of about 0.6 g on rock sites for a 2475 year return period in POS. Salazar et al [1] presented a high-resolution grid of H/V spectral ratios employing 1181 mobile microtremors at Port of Spain in order to retrieve the S-wave fundamental periods of vibration of the soil and proposed a microzonation map for the city and the correspondent seismic coefficients for building design. So the main objective of this article is to validate such periods through an alternative geophysical method, namely, the microtremors array, and use them to develop a liquefaction hazard map for the city based on the same H/V spectral ratios of microtremors.…”

Section: Methods and Data 11 Array Measurement Of Microtremorsmentioning

confidence: 99%

“…We calculated the observed horizontal-to-vertical spectral ratio (H/V) employing the resultant vector of the orthogonal north-south and east-west components of motion and averaging the results for all the stationary parts selected for each record (details of the digital processing of single mobile microtremors are explained [1]). To compute the synthetics' H/V ratios employing the DFA in Eq.…”

Section: H/v Interpretations: the Diffuse Field Approach And The Ellimentioning

confidence: 99%

“…The authors computed the liquefaction potential using Eq. (14) at each point and develop an iso-liquefaction potential map interpolating the K g value of the 1181 single mobile microtremors data employed in Salazar et al [1] (Figure 13). The results are very concerning regarding this hazard because the water table in POS can be found just at the surface, the soil conditions then are saturated sands and gravels, and sometimes poorly consolidated reclaimed land has been placed specially in the coastal areas.…”

Section: Preliminary Assessment Of Liquefaction Susceptibilitymentioning

confidence: 99%

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Estimation of Shear Wave Velocity Profiles Employing Genetic Algorithms and the Diffuse Field Approach on Microtremors Array: Implications on Liquefaction Hazard at Port of Spain, Trinidad

Salazar¹,

Mannette²,

Reddock³

et al. 2019

Natural Hazards - Risk, Exposure, Response, and Resilience

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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.

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Section: Discussionsupporting

confidence: 74%

mentioning

confidence: 59%

Section: Methods and Data 11 Array Measurement Of Microtremorsmentioning

confidence: 99%

Section: H/v Interpretations: the Diffuse Field Approach And The Ellimentioning

confidence: 99%

Section: Preliminary Assessment Of Liquefaction Susceptibilitymentioning

confidence: 99%

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Estimation of Shear Wave Velocity Profiles Employing Genetic Algorithms and the Diffuse Field Approach on Microtremors Array: Implications on Liquefaction Hazard at Port of Spain, Trinidad

Salazar¹,

Mannette²,

Reddock³

et al. 2019

Natural Hazards - Risk, Exposure, Response, and Resilience

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The Trinidad and Tobago Microzonation Project: Port of Spain

Papadopoulos

Reddock

Manzano

et al. 2020

Geophysical Journal International

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SUMMARY In 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.

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A Caribbean and Central America Seismic Hazard Model for Sovereign Parametric Insurance Coverage

Salgado‐Gálvez¹,

Ordaz

Singh

et al. 2022

Bulletin of the Seismological Society of America

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A fully probabilistic seismic hazard model with a single domain and sufficiently accurate resolution level for national analyses has been developed, for the Caribbean and Central America, to support the design of parametric earthquake policies offered by the Caribbean Catastrophe Risk Financing Facility to sovereign countries. This model provides updated earthquake hazard and risk information for 34 countries in the region, allowing to obtain detailed seismic hazard results at any location within the area of analysis. Besides a detailed zonation of subduction and crustal sources, updated seismicity and tectonic data have been utilized. Different seismicity, geometric, and rupture models have been adopted using state-of-the-art methodologies and tools. The main output of this model is a stochastic event-set, which is the hazard representation utilized not only to compute a long-term overview of the seismic hazard in the region but also to probabilistically estimate earthquake modeled losses at a national level that are used as triggers for underpinning parametric earthquake insurance. Although not of direct interest for parametric insurance purposes, this model also yields hazard maps and uniform hazard spectra for different return periods. For the operational purposes of the parametric insurance coverage, a postevent tool was developed to calculate, in near-real time, the ground-motion intensities associated with any earthquake within the region under study. This is done automatically by choosing a rupture plane from the moment tensor solution based on predefined rules while maintaining full consistency with all the assumptions made in the probabilistic seismic hazard analysis. The predicted ground motions in the region and the vulnerability functions developed for the exposed assets are then used to estimate whether the economic losses for each affected country exceed the trigger value stated in the country-specific insurance policy conditions and whether a payout should be issued, which is typically disbursed within 14 days.

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High-resolution grid of H/V spectral ratios and spatial variability on microtremors at Port of Spain, Trinidad

Cited by 6 publications

References 14 publications

Estimation of Shear Wave Velocity Profiles Employing Genetic Algorithms and the Diffuse Field Approach on Microtremors Array: Implications on Liquefaction Hazard at Port of Spain, Trinidad

Estimation of Shear Wave Velocity Profiles Employing Genetic Algorithms and the Diffuse Field Approach on Microtremors Array: Implications on Liquefaction Hazard at Port of Spain, Trinidad

The Trinidad and Tobago Microzonation Project: Port of Spain

A Caribbean and Central America Seismic Hazard Model for Sovereign Parametric Insurance Coverage

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