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Subduction ground motions in northern South America are about a factor of 2 smaller than the ground motions for similar events in other regions. Nevertheless, historical and recent large-interface and intermediate-depth slab earthquakes of moment magnitudes Mw = 7.8 (Ecuador, 2016) and 7.2 (Colombia, 2012) evidenced the vast potential damage that vulnerable populations close to earthquake epicenters could experience. This article proposes a new empirical ground-motion prediction model for subduction events in northern South America, a regionalization of the global AG2020 ground-motion prediction equations. An updated ground-motion database curated by the Colombian Geological Survey is employed. It comprises recordings from earthquakes associated with the subduction of the Nazca plate gathered by the National Strong Motion Network in Colombia and by the Institute of Geophysics at Escuela Politécnica Nacional in Ecuador. The regional terms of our model are estimated with 539 records from 60 subduction events in Colombia and Ecuador with epicenters in the range of −0.6° to 7.6°N and 75.5° to 79.6°W, with Mw≥4.5, hypocentral depth range of 4 ≤  Zhypo ≤ 210 km, for distances up to 350 km. The model includes forearc and backarc terms to account for larger attenuation at backarc sites for slab events and site categorization based on natural period. The proposed model corrects the median AG2020 global model to better account for the larger attenuation of local ground motions and includes a partially non-ergodic variance model.

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Swelling behavior of clays is of great importance for numerous engineering applications due to the prevalence of expansive clays around the world. Expansive clays are present in Mexico City, United States, Australia, Africa and South America, among others. In some cases, these types of clays could present swell pressure values greater than 400 kPa. In this technical note, correlation equations are developed to estimate the swell pressure of clays using laboratory tests performed on swelling clays in the city of Barranquilla, Colombia. Correlations are based on Atterberg limits and water content among other soil properties. Equations with statistically significant coefficients were selected and compared with equations found in the literature. Developed correlations evidenced that swell pressure decays quickly as water content increases. It was found that for the studied soils, Atterberg Limits did not present statistical significance in the estimation of swell pressure. Correlaciones empíricas para la determinación de la presión de expansión de arcillas expansivas en Barranquilla, Colombia ResumenEl comportamiento expansivo de las arcillas presenta vital importancia alrededor del mundo, ya que este tipo de arcillas se encuentras en diversas y extensas zonas del planeta. Arcillas con este tipo de comportamiento se encuentran presentes en diversas regiones del mundo como la ciudad de México, los Estados Unidos, Australia, algunas zonas de África y Sudamérica, entre otras. Este tipo de arcillas pueden presentar en algunos casos presiones de expansión superiores a los 400 kPa. En la presente nota técnica se desarrollan correlaciones para estimar la presión de expansión de arcillas con base en ensayos de laboratorio practicados a arcillas con comportamiento expansivo presentes en la ciudad de Barranquilla, Colombia. Las correlaciones desarrolladas se basan en los límites de Atterberg y contenido de humedad, entre otras propiedades de los suelos. Se seleccionaron aquellas ecuaciones que presentaban coeficientes estadísticamente significativos y se realizaron comparaciones con correlaciones presentes en la literatura. Las correlaciones mostraron que la presión de expansión decae rápidamente a medida que el contenido de humedad aumenta. Además, se observó que para los suelos estudiados los límites de Atterberg no son estadísticamente significativos para la estimación de la presión de expansión.

Crustal earthquakes are some of the main contributors to the seismic hazard in northern South America (NoSAm). There is evidence of historical crustal events with epicenters near populated cities, such as the 1999 Mw 6.2 Coffee Region earthquake, whose damages added up to 1.9% of Colombia’s gross domestic product and reported about 1200 deaths. Because the global crustal ground-motion models (GMMs) routinely used in seismic hazard assessments of the region are biased with respect to the available ground-motion records, this article presents a regional GMM developed using local data from earthquakes in Colombia, Ecuador, and Venezuela. The filtered database contains 709 triaxial records from 56 earthquakes, recorded at 92 stations between 1994 and 2020 by the Colombian Geological Survey. The moment magnitudes of the events range between 4.5 and 6.8, with hypocentral depths ≤60 km. The model covers rupture distances ≤350 km. The model site amplification is based on a categorization approach relying on the predominant site period, identified through the horizontal-to-vertical response ratios of 5%-damped response spectra. The proposed GMM is developed as a regionalization of the global Next Generation Attenuation-West2 Project ASK14 model. Our model corrects the misfit of the ASK14 GMM with respect to the observed ground-motion data in NoSAm for moderate magnitudes and intermediate to large distances while keeping the extrapolation capabilities. The proposed GMM considers the added attenuation for ray paths crossing the volcanic arc. Analysis of the variance components allows approximating plausible reductions of the standard deviation in future nonergodic models.