Assessing Susceptibility to Soil Liquefaction Using the Standard Penetration Test (SPT)—A Case Study from the City of Portoviejo, Coastal Ecuador

The city of Portoviejo in coastal Ecuador was severely affected during the 16 April 2016, Pedernales earthquake (Mw 7.8). Various coseismic liquefaction phenomena occurred, inducing lateral spreading, sand boils, ground subsidence, and sinkholes in soils with poor geotechnical quality in the alluvial and alluvial–colluvial sedimentary environment. Therefore, the main aim of this study was to collect data from standard penetration tests (SPT) and shear velocity and exploratory trenches and to calculate the liquefaction potential index (LPI) by considering a corresponding seismic hazard scenario with an amax = 0.5 g. From these data, a liquefaction hazard map was constructed for the city of Portoviejo, wherein an Fs of 1.169 was obtained. It was determined that strata at a depth of between 8 and 12 m are potentially liquefiable. Our quantitative results demonstrate that the city of Portoviejo’s urban area has a high probability of liquefaction, whereas the area to the southeast of the city is less sensitive to liquefaction phenomena, due to the presence of older sediments. Our results are in accordance with the environmental effects reported in the aftermath of the 2016 earthquake.This research was jointly supported by the Technical University of Manabí in Ecuador. With the particular support of the Soil and Concrete Mechanics laboratory “Suelcon & Asf”

ANALYSIS OF LOCAL RISK PERCEPTION IN THE EVENT OF A TSUNAMI – A CASE STUDY IN MANTA, COASTAL ECUADOR

Local perception of risk is a determinant of urban vulnerability. Accordingly, this research addresses the analysis of local perception of the risk of tsunami hazards occurrences and this case study focuses on an area of the Tarqui parish in the city of Manta in coastal Ecuador. This work also presents the possible tsunamigenic seismic source in the subduction zone of the study area. The Tarqui Zone is located within a coastal and fluvial landscape that currently the enlargement of the urban limit has obstructed the free flow of these systems. Based on the tsunami hazard map for the city of Manta, we determined that there are 392 sites in an area with high susceptibility to flooding. There are also 996 sites with medium susceptibility to floods in a zone of maximum influence between the levels of 7 to 20 m.a.s.l, sites in which the flood processes and corresponding erosion may not be very intense. In addition, the perception of this hazard was strengthened using context indicators on local tsunami risk perception based on a survey format for heads of households. In this regard, the given surveys indicate that 29 per cent of the population is in a state of high vulnerability, 63 per cent are in a situation of medium vulnerability and only 8 per cent are in a position of low vulnerability. With the obtained results we realized curves of frequency of perception of the population regarding this hazard, which will serve for the authorities to improve their response plans

Soil Liquefaction and Other Seismic-Associated Phenomena in the City of Chone during the 2016 Earthquake of Coastal Ecuador

The city of Chone, being situated on the Ecuadorian coast, was affected due to the close-by epicenter of the earthquake of 16 April 2016, which reached a magnitude of Mw 7.8. This catastrophic event presented settlements in the ground, sand boils and land subsidence, being the most damaging in a variety of civil works among these several buildings. The main objective of the current study is to select data using the standard penetration test (SPT) for the evaluation of the probability of liquefaction considering a maximum acceleration seismic risk of amax = 0.5 g. With the tabulated information, a liquefaction hazard map was generated for the city of Chone, where a safety factor of 1228 was obtained, determining the potentially liquefiable strata at an approximate depth between 9 and 11 m. Hereby, we were able to demonstrate results that were obtained experimentally through a quantitative analysis, indicating that the urban area of the city of Chone has a high probability of liquefaction, which was supported due to the presence of Holocene-aged soils developed in alluvial deposits, located in an alluvium mid catchment area. This novel research, due to the combination of a variety of used tools in the seismic risk evaluation, provides a relevant contribution to territorial planning and risk management in construction, in addition to the territorial reorganization of the canton as an example for different regions worldwide with similar geodynamics, soil mechanics and seismic vulnerabilities.This research was performed with the support of the private Soil Mechanics Laboratory “Suelcon & Asf” of the province of Manabi

Sedimentological study of distal rain- triggered lahars: the case of west coast of Ecuador

 In this paper we present geological evidence of secondary rain triggered lahar that affected the central coast of Ecuador in the last 2ky. Eight main ash units were described in the field and then physically and petrographically characterized in the laboratory. The units present four main kinds of deposits testifying different depositional processes and the palaeotopographic condition of these sectors of Ecuador. The deposits recognized on the field are associable with granular flows with a high amount of water that compared with similar cases in the world not exceed run-out of 40km. The lateral variation inside the deposits recognized, considering the thickness and the distance from the main Holocene volcanoes (>160km), allows us to relate with secondary rain-triggered lahars and not with primary lahars. The presence of fine-grained ash of mm to the cm-thick layer above a cm to meter thick sand to gravel layer point out that these deposits are linked with single events and not with a continuous river sedimentation process. These events were triggered by rain that remobilized distal fallout deposits linked with the last 2ka eruptive activities of the Ecuadorian volcanoes as Quilotoa, Cotopaxi and Guagua Pichincha. Several units were identified in the deposits studied, and particularly it is possible to observe in one of them lateral variations of the deposits that permit to localize the debris flow body related to the secondary rain triggered lahar. The body of the debris flow is present in the coastal sector comprise between Crucita and Jama and it shows a lateral change in lithofacies related to different palaeo topographic conditions. In conclusion, in this paper, we show how the formation of secondary rain triggered lahar can occur in the coastal sector of Ecuador principally near the main river but also in flat topographic condition. Moreover, the presence of human bones and porcelain fragments also confirms that in the past, these events strongly affected old civilizations. Different municipalities as Manta, Bahia, San Vincente, Canoa, and Jama are undoubtedly exposed today to this kind of hazard. Further researches must be focused on the evaluations of the lahar volumes that can affect the coastal area of Ecuador

Evaluación de riesgo costero y registros climáticos MIS 1 a MIS 3 en la costa central del Ecuador

Los análisis estratigráficos, biológicos y geoquímicos han proporcionado suficiente información para reconstruir la evolución paleográfica y climática de la costa del cantón Jaramijó. Uno de los resultados más notables, es la identificación y delineación de un paleo-acantilado costero de edad(14C) 43.245 ± 460 B.P.(perteneciente al MIS-3).Este MIS-3 es asociado a una época de glaciación, pero los datos obtenidos e interpretados en este estudio nos indican que la costa central del Ecuador registra un nivel interestadial(años cálidos en una etapa glacial).Dos acantilados más han sido cartografiados desde análisis de orthofotos, pero estos son de menor edad. La reciente transgresión holocénica ha modificado la costa central del Ecuador e incrementando el nivel de riesgo costero climático por las variaciones del nivel de mar. Paleo-línea de costas han sido evidenciados en los veriles-5.5m y-7.6m, a 440 y 650 m de distancias de la línea de costa actual. Para el sitio de Jaramijó, la tasa de retroceso de los acantilados está en el orden de 1.1 a 2.4m/año. Estas tasas de erosión pueden incrementarse si se consideran modelos matemáticos que estiman un escenarioenel2100deincrementosdel nivel de mar en +1 y +1.4

Evaluación estructural y rehabilitación sísmica del hotel samarina de propiedad de la universidad península de santa elena, para la creación de un modelo disipador de energía

El Hotel Samarina está ubicado frente al mar, en la cota +12 m s.n.m., en el cantón La Libertad, Provincia de Santa Elena. Fue construido al final de la década de los 50. El hotel Samarina terminado en un 70%, se compone de planta baja y tres pisos altos y estructuras de hormigón armado. La superficie total del mencionado hotel es de 2638 m2. Actualmente, se conoce que en el Ecuador y principalmente en la Provincia de Santa Elena, presenta una alta sismicidad por estar ubicada cercana a la zona de subducción de la placa de nazca y la placa sudamericana. A través de una evaluación y diagnóstico estructural, conforme a las normas ecuatorianas NEC 2011 o códigos uniformes de edificación UBC 97 la actual edificación no cumple el diseño sismoresistente, y de acuerdo al conocimiento actual se elaboró un diseño moderno donde se mejoró su nivel de desempeño o comportamiento sismo resistente ante la acción de un sismo moderado, y con la aplicación de un software libre denominado ETAB's se implementó un modelo con sistema de reforzamiento, compuesto de disipadores de energía colocados en las caras laterales y reforzamiento de columnas en los cuatro niveles que componen el edificio

Cenizas de cascarilla de arroz para la activación alcalina de cementantes binarios (ceniza volante/escoria de alto horno)

Se fabricaron morteros de activación alcalina basados en ceniza volante clase F y escoria de alto horno, conel fin de estudiar el efecto de una fuente alternativa de sílice sobre sus propiedades de fluidez y resistencia acompresión. Ceniza de cascarilla de arroz y silicato de sodio, en combinación con hidróxido de sodio, fueronlas soluciones químicas empleadas para la activación alcalina de los morteros. La información mineralógica yestructural de los sistemas activados alcalinamente fue obtenida mediante difracción de rayos X (DRX), mientrasque el análisis de sus propiedades en estado fresco se llevó a cabo a través del estudio de la fluidez.Además se evaluaron las propiedades mecánicas de las morteros a 28 días por médio del ensayo de resistenciaa compresión. Se encontró que los morteros activados con ceniza de cascarilla de arroz en combinacióncon hidróxido de sodio presentaron resistencias a compresión hasta 25% mayores en comparación con losmorteros activados con silicato de sodio /hidróxido de sodio. Finalmente fueron propuestas ecuaciones parala predicción de las resistencias a compresión de los morteros en función del tipo de activador. Este estudioconcluye que es posible utilizar cenizas de cascarilla de arroz como una fuente alternativa de sílice para procesosde activación alcalina.Palavras-chave: Ceniza de cascarilla de arroz, activación alcalina, ceniza volante, escoria de alto horno, resistenciaa compresión

InSAR-Based Mapping to Support Decision-Making after an Earthquake

It has long been recognized that earthquakes change the stress in the upper crust around the fault rupture and can influence the behaviour of neighbouring faults and volcanoes. Rapid estimates of these stress changes can provide the authorities managing the post-disaster situation with valuable data to identify and monitor potential threads and to update the estimates of seismic and volcanic hazard in a region. Here we propose a methodology to evaluate the potential influence of an earthquake on nearby faults and volcanoes and create easy-to-understand maps for decision-making support after large earthquakes. We apply this methodology to the Mw 7.8, 2016 Ecuador earthquake. Using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and continuous GPS data, we measure the coseismic ground deformation and estimate the distribution of slip over the fault rupture. We also build an alternative source model using the Global Centroid Moment Tensor (CMT) solution. Then we use these models to evaluate changes of static stress on the surrounding faults and volcanoes and produce maps of potentially activated faults and volcanoes. We found, in general, good agreement between our maps and the seismic and volcanic events that occurred after the Pedernales earthquake. We discuss the potential and limitations of the methodology

InSAR-Based Mapping to Support Decision-Making after an Earthquake

It has long been recognized that earthquakes change the stress in the upper crust around the fault rupture and can influence the behaviour of neighbouring faults and volcanoes. Rapid estimates of these stress changes can provide the authorities managing the post-disaster situation with valuable data to identify and monitor potential threads and to update the estimates of seismic and volcanic hazard in a region. Here we propose a methodology to evaluate the potential influence of an earthquake on nearby faults and volcanoes and create easy-to-understand maps for decision-making support after large earthquakes. We apply this methodology to the Mw 7.8, 2016 Ecuador earthquake. Using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and continuous GPS data, we measure the coseismic ground deformation and estimate the distribution of slip over the fault rupture. We also build an alternative source model using the Global Centroid Moment Tensor (CMT) solution. Then we use these models to evaluate changes of static stress on the surrounding faults and volcanoes and produce maps of potentially activated faults and volcanoes. We found, in general, good agreement between our maps and the seismic and volcanic events that occurred after the Pedernales earthquake. We discuss the potential and limitations of the methodology.This work is supported by the European Commission, Directorate-General Humanitarian Aid and Civil Protection (ECHO) under the SAFETY (Sentinel for Geohazards regional monitoring and forecasting) project (ECHO/SUB/2015/718679/Prev02) and by the Spanish Ministry of Economy and Competitiveness under INTERGEOSIMA (CGL2013-47412) and ACTIVESTEP (CGL2017-83931-C3), QUAKESTEP (1-P) + 3GEO(2-P) + GEOACTIVA (3-P) projects

THE 7.8 Mw EARTHQUAKE AND TSUNAMI OF 16th April 2016 IN ECUADOR: Seismic Evaluation, Geological Field Survey and Economic Implications

We evaluated the recent earthquake and tsunami responsible for considerable damage and 663 deaths due to a 7.8Mw movement on the 16th of April 2016. The seismic event filled tens of thousands in refugee camps and affected some two million persons directly. The potential of high losses and damage with a total of 29,672 properties, including family houses, is also given by the fact that the infrastructure of the fishing, tourism and other industries and the movement to live along the beaches, have been highly developed within the last decades along the Ecuadorian coasts. The geological survey and determination of field data were performed three days after the main seismic event, allowing to obtain 290 data coseismic effects on the ground that allowed to evaluate the maximum macroseismic intensities as well as the predominant geomorphological features.The results of these sampling stations allowed to reconstruct a geological map with isoseismals fields of intensities. With all the compiled and recorded coseismic data in the field of higher macroseismic intensities, we proceeded to produce a map of intensities applying the definitions and degrees of the ESI 2007 scale. We also evaluated the distribution and intensities of the aftershocks demonstrating the spatial- temporal affinities. The occurred tsunami, although less destructive than previous in the same region has been documented with all details available. The economical assessment included in this study concludes that this earthquake impacted a large part of a variety of coastal cities destroying between 70 and 80% of some close-by villages and cities with a distance of 140-150 km of the epicenter, which suffered damages of their buildings within 40 to 55%, in which lines of electricity transmission, infrastructure of water supply, hospitals, schools, private and public buildings, main roads and highways have been severely affected or even completely destroyed. The costs of the damages of the mentioned infrastructure are summing up an approximate loss of some 3.3 billion USD, being equivalent to 3.31 % of the Ecuadorian GDP. In addition to losses in infrastructure and properties, over 28 thousand jobs were lost and about 300 million US$ in trade and businesses