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Site characterization and seismic zonation of Guayaquil city, Ecuador

Abstract:

Guayaquil is one of the most important cities in Ecuador and has a significant earthquake hazard arising from three complex tectonic environments. It is located in the estuarine zone of the lower Guayas River, and the soil stratigraphy consists of deep soft sediments over hard rocks from the Cretaceous period. These deltaic-estuarine sediments were deposited in a brackish environment, and they are unusually weak and highly compressible. Microtremor measurements have been performed to estimate site periods and indicate significant spatial variability. Shear wave velocity (V s) measurements using the Spectral-Analysis-of-Surface-Waves (SASW) method were performed to better understand the variability of the site period map. Measurements were completed at 14 different sites to depths between 40 and 150 m, depending on spatial and source considerations. Additional site investigation, included cone penetration tests (CPT) and standard penetration tests (SPT) with energy measurements. This paper briefly describes the site characterization program and its implication on the seismic zonation of the city. The paper also presents preliminary correlations between the measured V s and in situ soil parameters for these soft soil deposits.