Integrated MASW and ERT Imaging for Geological Definition of an Unconfined Alluvial Aquifer Sustaining a Coastal Groundwater-Dependent Ecosystem in Southwest Portugal

This paper integrates multichannel analysis of surface waves (MASW) and time-lapse electrical resistivity tomography (ERT) to define aquifer geometry and identify transient groundwater features of the Cascalheira Stream Basin Holocene alluvial aquifer (aquifer H), which contributes to the Santo André Lagoon, part of a coastal groundwater-dependent ecosystem (GDE), located in southwest Portugal. MASW measures shear-wave velocity (VS), allowing one to obtain steady geological models of the subsurface, and ERT measures subsurface electrical resistivity (ER), being subjected to ambient changes. MASW enables disambiguation of geological structures in low ER environments, such as coastal areas. This research covered one natural year and involved one MASW campaign, four ERT campaigns, and additional geological field surveys and groundwater monitoring to assist interpretation of results. In the area, the conjugate NW–SE and NE–SW strike-slip fault systems determine compartmentalization of geological structures and subsequent accommodation space for Holocene sedimentation. MASW and ERT surveys show how the NW–SE system deepens these structures toward the coast, whereas the NE–SW system generates small horsts and grabens, being one of these occupied by aquifer H. From upstream to downstream, aquifer H thickness and width increase from 10 m to 12 m and from 140 m to 240 m, respectively. Performance of VS and ER models was satisfactory, with a normalized error of the VR and ER models in the 0.01–0.09 range, meaning that a quantitative quota of uncertainty can be segregated from the overall uncertainty of groundwater models without substantially affecting its simulations accuracy. This methodology seeks to improve the design of shallow groundwater research in GDE preservation policies.info:eu-repo/semantics/publishedVersio

Sistema combinado para la adquisición de las velocidades de ondas de comprensión y de ondas Rayleigh y para la generación de secciones Vs, Vp y de parámetros geomecánicos del subsuelo

Número de publicación: 2 524 736 Número de solicitud: 201430234La invención se refiere a un sistema para la adquisición de datos sísmicos producidos por ondas superficiales, u ondas Rayleigh, y ondas de compresión, u ondas P, de forma rápida y efectiva en zonas urbanas de alto tráfico vehicular, por ejemplo zonas donde existen cruces, rotondas, o pasos peatonales. Dicho sistema comprende, preferentemente, una manguera (1) conectada a un dispositivo de arrastre (2), y equipada con una pluralidad de geófonos (5) conectados mediante un cable principal (9) a una unidad de medida y registro (4). Asimismo, el sistema comprende una pluralidad de placas de golpeo (7) dispuestas e intercaladas entre los geófonos (5) para la generación de las ondas de compresión u ondas P.Universidad Politécnica de Cartagen

Shear-wave velocity structure from MASW and SPAC methods. The case of Adra town, SE Spain

The damage distribution in the town of Adra (south-eastern Spain) during the 1993 and 1994 Adra earthquakes, magnitude Mw 5.0 and maximum intensity degree of VII (European Macroseismic Scale), was mainly concentrated in the southeast sector, where low-diagenetic (soft) sediments outcrop. As new urbanizations are planned in that sector, a soil classification based on the shallow shear-wave velocity (Vs) structure is needed. For the purpose of earthquake disaster mitigation, the Spatial Autocorrelation (SPAC) and the Multichannel Analysis of Surface Waves (MASW) methods were used to propose integrated 2D Vs models for the seismic response characterization of shallow geology. Joint inversion of H/V spectral ratios of ambient noise, interpreted under the Diffuse Field Approach, and dispersion curves derived from the SPAC method allowed to obtain more constrained models. Both, SPAC and MASW methods provided similar results for the surveyed geological formations. From these models, a classification of the geological formations has been carried out in terms of Vs30 values and Eurocode 8 (EC8, 1998) classes. Lower Vs30 values in the 180-360 m/s range were found in the southeastern sector of the town, where soft sediments outcrop and some building damage was reported from the 1993-1994 earthquakes. The highest Vs30 values above 800 m/s appear at the northern sector, where the hardest rocks outcrop and no building damage was reported. The combination of the well-suited Vs database prepared for different geological formations with the 1:5,000 scale geological mapping was a step to obtain a detailed soil microzonation map of Adra. It gives a new predictive insight into the building damage distribution, which will contribute to the appropriate urban planning of the future growth of the town

Combining of MASW and GPR Imaging and Hydrogeological Surveys for the Groundwater Resource Evaluation in a Coastal Urban Area in Southern Spain

This paper conceptualizes and evaluates the groundwater resource in a coastal urban area hydrologically influenced by peri-urban irrigation agriculture. Adra town in southern Spain was the case study chosen to evaluate the groundwater resource contributed from the northern steep urban sector (NSUS) to the southern flat urban sector (SFUS), which belongs to the Adra River Delta Groundwater Body (ARDGB). The methodology included (1) geological and hydrogeological data compilation; (2) thirteen Multichannel Analysis of Surface Waves (MASW), and eight Ground Penetrating Radar (GPR) profiles to define shallow geological structures and some hydrogeological features; (3) hydrogeological surveys for aquifer hydraulic definition; (4) conceptualization of the hydrogeological functioning; and (5) the NSUS groundwater resource evaluation. All findings were integrated to prepare a 1:5000 scale hydrogeological map and cross-sections. Ten hydrogeological formations were defined, four of them (Paleozoic weathered bedrock, Pleistocene littoral facies, Holocene colluvial, and anthropogenic filling) in the NSUS contributing to the SFUS. The NSUS groundwater discharge and recharge are, respectively, around 0.28 Mm3 year−1 and 0.31 Mm3 year−1, and the actual groundwater storage is around 0.47 Mm3. The groundwater renewability is high enough to guarantee a durable small exploitation for specific current and future urban water uses which can alleviate the pressure on the ARDGB

Desarrollo e implementación de métodos avanzados de exploración sísmica activa y pasiva, y del método del gradiente topográfico en el análisis de microzonificación sísmica en el sureste de la Península Ibérica

[SPA] En zonas sísmicamente activas, la ocurrencia de terremotos ocasiona cuantiosos daños materiales y en algunos casos incluso la pérdida de vidas humanas. Es por ello que la comunidad científica y las administraciones competentes realizan esfuerzos para que la ocurrencia de un terremoto importante provoque el menor daño posible sobre la población. Sin embargo, en muchas ocasiones el rápido crecimiento urbanístico se lleva a cabo sin los adecuados criterios preventivos lo cual hace que estas nuevas zonas urbanas sean muy vulnerables ante un terremoto, incluso de magnitud moderada. El sureste de la península Ibérica aúna ambos ingredientes: a una rápida expansión urbanística se suma la ocurrencia de terremotos de magnitud moderada (y en algunos casos, según los registros históricos, de gran magnitud). La serie sísmica ocurrida en Lorca (localizada en el sureste de la Península Ibérica) en 2011 puso de manifiesto que estos terremotos de magnitud moderada pueden provocar grandes daños. El valor promedio de velocidad de cizalla en los primeros 30 metros de profundidad (VS30) del terreno es un parámetro fundamental en la dinámica de suelos y en ingeniería sísmica, siendo determinante para clasificar las condiciones de sitio reflejadas en los códigos sísmicos (p.e. NEHRP-94, Eurocode 8 (EC8), NCSE-02). El uso de técnicas de prospección sísmicas, basadas en el registro del ruido ambiental (pasivas) y/o con el uso de fuentes sísmicas (activas), se ha extendido en los últimos tiempos. Entre ellas, el método de análisis multicanal de ondas superficiales (MASW), refracción por microtremores (REMI) o autocorrelación espacial (SPAC) son técnicas que se caracterizan por una rápida adquisición de datos y una mínima afección al medio urbano. En este estudio se ha obtenido y analizado la estructura superficial del terreno en las ciudades del sureste de la Península Ibérica (Lorca, Adra y Almería) mediante los métodos sísmicos MASW y SPAC. Los valores de VS30 obtenidos con estos métodos sísmicos fueron utilizados para crear nuevos mapas de clasificación del suelo de las ciudades de estudio, los cuales son necesarios en los estudios de microzonificación sísmica. Con el fin de realizar mediciones en el área urbana de estas ciudades se ha desarrollado un sistema land streamer, el cual ha permitido obtener datos sísmicos con una alta productividad utilizando el método MASW. Finalmente, se ha utilizado el método del gradiente topográfico para estimar los valores de VS30 del terreno. Los resultados obtenidos con el método del gradiente topográfico, considerando las ciudades de estudio como regiones tectónicamente activas, muestran una buena correlación con los resultados obtenidos con los métodos sísmicos. Estos resultados ponen de manifiesto que, bajo determinadas condiciones y con un modelo digital del terreno (MDT) adecuado, el método de gradiente topográfico puede ser una alternativa para aquellas áreas del mundo donde no se tenga un acceso adecuado a las técnicas de prospección sísmica de mayor detalle y más costosas que se vienen aplicando en la actualidad. Los parámetros del movimiento sísmico del terreno se han calculado utilizando sismogramas sintéticos como movimiento de entrada. La severidad del movimiento del suelo se ha cuantificado a través de la estimación de los valores de aceleración pico máxima (PGA), velocidad pico máxima (PGV), intensidad de Arias (AI), periodo predominante (Tp), e intensidad instrumental. Todos estos parámetros se basan en la estructura de velocidad de ondas de cizalla obtenida con los métodos sísmicos.[ENG] In seismically active zones, the occurrence of earthquakes produces substantial economic losses and sometimes important human lives casualties. In light of this, the scientific community and governments devote significant efforts with the aim of minimizing the negative impact of major earthquakes related to local economies and population. However, the rapid growth of inhabited areas is not always followed with the appropriate development of prevention standards, making newly developed urban areas very vulnerable to earthquakes of even moderate magnitude. For instance, the south-eastern part of the Iberian Peninsula has these two ingredients: a rapid urban growth and the existence of moderate and (according to historic records) major seismic activity. Indeed, the seismic series that took place in Lorca (located in the SE of the Iberian Peninsula) in 2011 showed that even a moderate magnitude earthquake may cause very serious damages on buildings and human losses. Besides, the average values of the shear-wave velocity of the upper 30 m (VS30) of the soil is a critical parameter in soil dynamics and earthquake engineering which is determined to classify site conditions reflected in seismic codes (e.g. NEHRP-94, Eurocode 8 (EC 8), NCSE-02). The use of prospecting techniques has been extended in recent times, based on environmental noise measurements (passive) and seismic head-waves creation sources (active). Among them Multichannel Analysis of Surface Wave (MASW), Refraction Microtremor (ReMi), and Spatial Autocorrelation (SPAC) are seismic methods characterized by a rapid data acquisition and minimal impact on the urban environment. In this study we have obtained and assessed the subsurface structure of the cities of Lorca, Adra and Almería by means of seismic methods (MASW and SPAC). The VS30 values obtained from seismic method were used to create a new soil classification map of these cities which is suitable for microzoning purposes. In order to perform measurements in the urban area of these cities a towed land-streamer was developed to gather seismic data with high productivity using the MASW method. Also, it has been used the topographic slope method to estimate the value of VS30. The results obtained by the topographic slope estimation, considering as active tectonic region, show significant similarity to those obtained by the seismic methods. These results demonstrate that under certain conditions and with an adequate Digital Elevation Model (DEM) the topographic slope method can be a good alternative for those areas of the world with limited economic resources that cannot apply traditional seismic prospecting techniques. Finally, strong ground motion parameters have been calculated using synthetic seismograms as input motion. The severity of subsurface motion has been quantified through the estimation of peak ground acceleration (PGA), peak ground velocity (PGV), Arias intensity (AI), predominant period (Tp), and instrumental intensity values of the ground motion, all of them based on shear-wave velocity structures obtained from the seismic methods.Universidad Politécnica de CartagenaPrograma de doctorado en Ingeniería del Agua y del Terren

Zonificación sísmica de la región de Lorca mediante el método del gradiente topográfico: resultados preliminares del proyecto de peligrosidad sísmica mediante técnicas geofísicas

La ocurrencia de un evento sísmico en una zona provoca daños en las edificaciones, que son función de la respuesta del terreno a las cargas cíclicas. Para estudiar este efecto sitio se está desarrollando un proyecto de I+D a plicado a la ciudad de Lorca (Murcia) sobre el diagnóstico local de la peligrosidad sísmica con el empleo de técnicas geofísicas. Los resultados preliminares de este proyecto se exponen en este artículo

Aplicación del método MASW para estudios sobre microzonificación sísmica en la ciudad de Lorca-España

Históricamente los terremotos han causado innumerables pérdidas de vida humanas y bienes materiales, estos daños siguen presentes actualmente y seguirán pasando en el futuro, con el inconveniente del crecimiento desproporcionado de la población que hace que los terremotos sean más catastróficos cuando ocurren en zonas densamente pobladas. Después de la ocurrencia de un terremoto se añaden otro tipo de problemas para los sobrevivientes que se han quedado sin hogar, problemas como soportar bajas temperaturas, incendios, robos, enfermedades relacionadas al agua y al medio en que viven. Más del 90% de las víctimas de los terremotos están relacionadas al derrumbamiento de edificios, por lo que es esencial que exista una buena calidad en la construcción de las viviendas para reducir los desastres, es por esto que es de suma importancia la evaluación de los peligros que amenazan una zona, peligros como derrumbes de laderas, zonas sísmicamente activas por estar sobre fallas geológicas, cercanía al mar en caso de producirse tsunamis, etc. Con la utilización de esta técnica se propone una caracterización del suelo que permitirá tomar en cuenta nuevos parámetros en la actuación ante riesgos sísmicos de edificios ya construidos y en la planificación del riesgo sísmico para nuevas zonas urbanizables.Centro Universitario de la Defensa. Escuela de Turismo de Cartagena. Escuela Técnica Superior de Ingeniería Industrial UPCT. Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT). Escuela de Ingeniería de Caminos y Minas (EICM). Escuela de Arquitectura e Ingeniería de Edificación (ARQ&IDE). Parque Tecnológico de Fuente Álamo. Navantia. Campus Mare Nostrum. Estación Experimental Agroalimentaria Tomás Ferro

Vs30 Structure of Almeria City (SE Spain) Using SPAC and MASW Methods and Proxy Correlations

The topographic slope method is an innovative, fast and very low-cost technique for estimating the average S-wave velocity in the upper 30 m (Vs30) based on the relationship between this quantity and the slope of the ground, obtained using a Digital Elevation Model (DEM). The method is based on the good linear correlations log(Vs30)–log(slope) found experimentally, which, ideally, should be determined for each region. If measured Vs30 data are not available to carry out this fitting for the study area, correlations from other areas could be used, although the reliability of the estimated Vs30 results would be lower. In this article, Vs30 observations are made for the city of Almeria, using Spatial Autocorrelation Surveys (SPAC) and Multichannel Analysis of Surface Waves (MASW), obtaining two types of fitting: (a) linear relationship log(Vs30)–log(slope); and (b) considering additional dependence on geological units. The reliability, evaluated by Multiple R-Squared (MRS), varies between 79.2% in the first case and 87.0% in the second, lowering the mean absolute values of the residuals at the observation points in the first case from 40.0 m/s to 29.0 m/s. Using a more generic correlation obtained for other areas of the world, the mean absolute residuals increase to 74.7 m/s

Potential damage and losses in a repeat of the 1910 Adra (Southern Spain) earthquake

The town of Adra (Almeria Province, South-Eastern Spain) has been seriously affected by historical damaging earthquakes in 1487, 1522, two in 1804 and in 1910 with epicentres offshore in the Alboran Sea that reached onshore an estimated maximum intensity of VIII, IX, VIII, VIII–IX and VII–VIII, respectively. Additionally, in the instrumental period, several seismic series near the city affected it with moderate structural damages like the recent one of 1993–1994, when two main earthquakes of magnitude 5.0 and 4.9 cause serious damage in mid-rise reinforced concrete buildings sited on soft soils. Consequently, the town can be affected by moderate to destructive earthquakes, so this paper provides an initial assessment of the potential impact and the consequences (in terms of structural damage, economic and human losses) if the 1910 Adra earthquake hit the city again. The results point out that buildings damage are mainly concentrated in the soft soils areas of the city and that the non-engineered buildings, especially the oldest one, have the highest vulnerability, and therefore, the structural damage is higher, while seismically designed structures show a better behaviour showing less damage. Additionally, mid- and high-rise buildings have more extensive damage than low-rise buildings. Besides, the reinforced concrete buildings with waffled-slab floors, built previously to the first Spanish seismic code (NCSE-94), show, also, important damage. In summary, we have obtained that 474 ± 160 and 973 ± 78 buildings will be affected by complete and extensive damage, respectively, that is around 40% of the buildings in the city.The authors wish to acknowledge the support of the Spanish research Projects CGL2011-30187-C02-02, BEST/2012/173, CGL2016-77688-R (AEI/FEDER,UE) and AICO/2016/098