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.

ABSTRACT Few moderate-to-strong earthquakes associated with active and capable geological faults have been documented for the southern coastal region of Ecuador. The seismic record of Ecuador initiates with the Guayaquil earthquake in 1787 (Mw 6.5), followed by the 1943 (Mw 6.2), and the most recent one in 1980 (Mw 6.1). The available data is insufficient to evaluate the seismic hazards associated with faults capable of generating seismic events of magnitude Mw≥6.0 in the region. Also, earthquakes of minor magnitudes can be disregarded as they do not induce significant ground coseismic effects. In this context, this study presents a catalog of geological faults, delineating 40 segments of capable and active faults on the sea floor of the Gulf of Guayaquil and inland segments of Guayas, Santa Elena, and El Oro provinces. This methodological approach estimates a variety of seismicity levels ranging between Mw 6.2 and Mw 7.2, with rock peak ground accelerations between 0.24 g and 0.41 g. These values have been obtained from empirical regression equations applied to the length of capable geological faults. The F-40 seismogenic structure located in the accretionary prism, close to the subduction zone, is capable of generating Mw 8.2 earthquakes and potentially causing coseismic ground damage to the city of Guayaquil located ca. 177 km to the NE. Furthermore, local tsunami hazards may affect severely areas that are densely populated, with developing industrial areas, on the coast of the Gulf of Guayaquil. This structural geological analysis provides useful new data for seismic hazard assessment.

RESUMEN Terremotos moderados a fuertes, asociados a la tectónica de fallas corticales, han sido poco documentados en la costa sur del Ecuador. La breve historia de registros sísmicos se inicia con el terremoto de Guayaquil, el 11 de junio de 1787 (Mw 6.5), seguido por los terremotos del 30 de enero de 1943 (Mw 6.2), y el 18 de agosto de 1980 (Mw 6.1). Este registro sísmico instrumental proporciona poca información para evaluar el riesgo sísmico por fallas capaces de generar sismos de magnitud mayor o igual a Mw 6.0. Este estudio presenta un catálogo de fallas, delineando 40 segmentos de fallas capaces en el fondo marino del Golfo de Guayaquil y segmentos continentales de Guayas, Santa Elena, y El Oro. Este procedimiento metodológico ha permitido estimar niveles de sismicidad con magnitudes que varían entre Mw 6,2 a Mw 7,2, y aceleraciones en roca, PGA, en el orden de los 0,24 g a los 0,41 g. Estos valores fueron obtenidos con ecuaciones de ajuste aplicadas a fallas geológicas capaces. La estructura sismogénica F-40 localizada en el prisma de acreción (junto a la zona de subducción) es capaz de generar un sismo de magnitud aproximada a Mw 8.2, pudiendo causar daños cosísmicos a la ciudad de Guayaquil, ubicada a aproximadamente a 177 km de distancia hacia el NE, y también generar tsunamis sobre áreas densamente pobladas, y sectores industriales, asentados en el borde costero del Golfo de Guayaquil. Toda esta información geológica estructural proporciona nuevos datos para considerar en los estudios de peligro sísmico.

ABSTRACT Alkali activated mortars made of class F fly ash and blast furnace slag were cast, in order to study the effect of an alternative source of silica on its properties of fluidity and compressive strength. Rice husk ash and sodium silicate solution, mixed with sodium hydroxide, were used for activation of mortars. The mineralogical and structural information of alkali activated systems was obtained by X-ray diffraction (XRD), while the analysis of fresh properties was carried out by means of fluidity test. The mechanical properties of mortars were assessed by 28 days compressive strength test. It was found that mortars activated with rice husk ash plus sodium hydroxide showed compressive strengths up to 25% higher that those activated with sodium silicate / sodium hydroxide. Finally, equations were proposed for the prediction of compressive strengths of mortars according to the type of activator. This study concludes that it is possible the use of rice husk ash as an alternative source of silica in alkaline activation process.

RESUMEN Se fabricaron morteros de activación alcalina basados en ceniza volante clase F y escoria de alto horno, con el fin de estudiar el efecto de una fuente alternativa de sílice sobre sus propiedades de fluidez y resistencia a compresión. Ceniza de cascarilla de arroz y silicato de sodio, en combinación con hidróxido de sodio, fueron las soluciones químicas empleadas para la activación alcalina de los morteros. La información mineralógica y estructural de los sistemas activados alcalinamente fue obtenida mediante difracción de rayos X (DRX), mientras que 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 resistencia a compresión. Se encontró que los morteros activados con ceniza de cascarilla de arroz en combinación con hidróxido de sodio presentaron resistencias a compresión hasta 25% mayores en comparación con los morteros activados con silicato de sodio /hidróxido de sodio. Finalmente fueron propuestas ecuaciones para la predicción de las resistencias a compresión de los morteros en función del tipo de activador. Este estudio concluye que es posible utilizar cenizas de cascarilla de arroz como una fuente alternativa de sílice para procesos de activación alcalina.

Resumen 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 2.4 m/año. Estas tasas de erosión pueden incrementarse si se consideran modelos matemáticos que estiman un escenario en el 2100 de incrementos del nivel de mar en +1 y +1.4m.

Abstract Stratigraphic, biological and geochemical analyzes have provided sufficient information to reconstruct the paleographic and climatic evolution of the coast of the Jaramijó canton. One of the most remarkable results is the identification and delineation of a paleo sea-cliff of age 14C 43,245 ± 460 B.P. (belonging to the MIS-3). This MIS-3 is associated with a period of glaciation, but the data obtained and interpreted in this study indicate that the central coast of Ecuador has an interstadial phase (warm years in a glacial stage). Two more paleo-coastal cliffs have been mapped from orthofotos analysis, but these are younger. The Holocene transgression has modified the central coast of Ecuador and increased the level of coastal climate hazard by sea-level rise. Paleo-coastlines have been evidenced in the depth contours of -5.5m and -7.6m, at 440 and 650 m distances from the up-to-date coastline. For the Jaramijó site, the rate of cliff-erosion and wave-cut platforms is in the order of 1.1 to 2.4 m/yr. These cliff-erosion rates can be increased if we consider mathematical models with an estimated sea-level rise scenario to be in 2100 of about +1 to +1.4m.