Person:
Muñoz Martín, Alfonso

First Name

Alfonso

Last Name

Muñoz Martín

URI

https://hdl.handle.net/20.500.14352/75220

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Geodinámica, Estratigrafía y Paleontología

Area

Geodinámica Interna

Identifiers

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Now showing 1 - 8 of 8

Análisis de nuevos datos gravimétricos marinos en el entorno de la Isla Decepción (Islas Shetland del Sur, Antártida)
(Revista de la Sociedad Geológica de España, 2001) Carbó Gorosabel, Andrés; Muñoz Martín, Alfonso; Martín Dávila, José; Catalán, Manuel; García, Alicia
La Isla Decepción es la parte emergida de un volcán muy joven y activo. Se encuentra situada en el SO del Estrecho de Bransfield, que separa la Península Antártica de las islas Shetland del Sur. En este trabajo se muestran los resultados del levantamiento gravimétrico realizado en la campaña de investigación geofísica marina DECVOL99 (Diciembre de 1999). El procesado de los 4906 datos seleccionados, obtenidos a lo largo de 48 líneas de navegación, ha permitido la realización de dos mapas de anomalías de Bouguer en el interior y en el exterior de la Isla Decepción. El tratamiento de los datos gravimétricos ha incluido, además de las correcciones habituales, la corrección topográfica terrestre y del fondo marino utilizando una malla de 1 km de lado. Los mapas de anomalías de Bouguer resultantes muestran una serie de anomalías y gradientes gravimétricos bien definidos que, al integrarlos con el resto de información existente, permiten su interpretación desde el punto de vista estructural y tectónico. De este modo las anomalías gravimétricas en el entorno de la Isla Decepción se encuentran definidas por una serie de mínimos y máximos con dos orientaciones principales NE-SO y NO-SE, que se corresponden bien con rasgos morfoestructurales y geofísicos en otros sectores del Estrecho de Bransfield. La mayor parte de los gradientes gravimétricos alargados y con carácter neto pueden ser interpretados como zonas de fractura NO-SE y NE-SO que limitan áreas de máximos y mínimos gravimétricos. Las anomalías positivas de gran longitud de onda constituyen la continuación hacia el SO de la corteza continental de la Isla Livingston, mientras que los máximos gravimétricos de alta frecuencia están asociados a bloques elevados y de alta densidad. Las zonas de mínimos valores de anomalía de Bouguer coinciden con los principales ejes de extensión y máximo relleno de materiales sedimentarios recientes. Las orientaciones y localizaciones de las bandas de alto gradiente gravimétrico permiten su correlación con zonas de fracturas definidas mediante otros datos geofísicos marinos, así como con la batimetría y los datos estructurales medidos en superficie.
Relación entre la complejidad estructural frágil y la distribución espacial de la sismicidad en tres regímenes tectónicos diferentes (Sur de Centro América)
(Geotemas, 2000) Muñoz Martín, Alfonso; Arcila, M.; Pérez López, Raúl; Rodríguez Pascua, Miguel Angel; Vicente Muñoz, Gerardo de
Fracturation process is the main geological mechanism for earthquakes generation as well as their magnitude and spatial distribution. In this work we analyze the correlation among a geometric, cinematic and dynamic fault-slip analysis with the magnitude frequency distribution (Ms) and the epicentral setting into three different tectonic areas. In order to compare all these parameters these areas have the same surface (2°x2°) and a similar number of epicentres. The brittle structural complexity has been defined by means an index which depends on the number of active structures as well as the different type of active faults under the present-day stress tensor. The obtained results seem indicate that a bigger index of brittle structural complexity has a good relationship with an increasing of the "b" value and with a bigger complexity in the spatial distribution of earthquakes defined by the fractal dimension (capacity dimension, Dcap).
Caracterización geoeléctrica de los depósitos superficiales en la Antártida Occidental (Isla Livingstone, Islas Shetland del Sur, Antártida Occidental)
(Geogaceta, 2000) Muñoz Martín, Alfonso; Giner Robles, Jorge; González Casado, José Manuel; López Martínez, Jerónimo; Durán Valsero, Juan José; Gumiel, Pablo; Serrano, Enrique
The geophysical study of superficial deposits (mainly gravels) in ice-free areas near the seashore in the South Shetland Islands (Antarctica) allows establishing the possible existence of permafrost and buried ice bodies. In this work we have investigated the internal structure of Quaternary sediments using the resistivity method (vertical electric sounding, V.E.S.), with the purpose of establishing the resistivity values of the different materials and their geometry. We present here the results obtained from 17 vertical electric soundings carried out in Caleta Española, (north coast of Hurd Peninsula), and in the surroundings of Caleta del Glaciar Rocoso (south coast of Hurd Peninsula), both in Livingston Island. Vertical electric soundings interpretation has allowed us to characterise different units from the resistivity values (active layer, permafrost, buried ice, Quaternary deposits and their basement), and to establish the inter-phase between sea water and continental water. Moreover, with the resistivity method we have deduced the spatial distribution of some of these beds. In this way the permafrost (with resistivity values ranging between 13000 and 35000 Ω*m), and the associated active layer, is restrained to shallow depths(< 2 m) and located in the surveyed areas faraway from the seaside (i.e. mainly in the upper raised beaches). Buried ice under coarse Quaternary deposits have resistivity values of one major order magnitude than the permafrost (> 60000 Ω *m) and has been only found in the studied rock glacier.
Marco geotectónico para el noroeste de Sur América y Sur de Centro América
(Geotemas, 2000) Arcila, M.; Muñoz Martín, Alfonso; Vicente Muñoz, Gerardo de
Due to the convergence of four major plates (Nazca, South America, Cocos and Caribbean) with a group of minor blocks between Central and South America region, it is a tectonic complex area. These small plates have different relative movements respect to the main Plates. Since 1969 a group of tectonic models including different plate borders and kinematic relationships have been proposed. Nowadays there are several databases with homogeneous quality including seismicity, topography, CPS and magnetic anomalies. These databases allow building a new geotectonic model by means of the integration of all o f them. We have analyzed the topography, seismicity, actual stress regimes and plate kinematics in order to propose a new geotectonic model at the south of Central America and the northwester of South America.
Rango de Magnitudes de esfuerzos tectónicos en una zona intraplaca: el macizo de El Berrocal, borde sur del Sistema Central Español
(Geogaceta, 2002) Martín Velázquez, Silvia; Vicente Muñoz, Gerardo de; Muñoz Martín, Alfonso; Elorza Tenreiro, Francisco Javier; Vela Guzmán, Antonio
Stress magnitudes throughout a NW-SE cross-section in El Berrocal granitic massif (Spanish Central System) have been analysed by means of finite element modelling. Topographic surface, lithological differences and recent compressive tectonic stresses have been inc!uded. Two kinds of models have been performed to study the influence of rheologic properties, one with average cortical mechanical properties and the other with the main lithologies. Horizontal tectonic stress magnitudes obtained in the last model have been checked with the recent stress ratio got by stress inversion of fault slip data. Horizontal tectonic load that better fits recent tectonic stress distribution is in the range of 10-15 MPa.
Características de los tensores de esfuerzos activos entre la Dorsal Centroatlántica y la Península Ibérica
(Geotemas, 2000) Vicente Muñoz, Gerardo de; Martín Velázquez, Silvia; Rodríguez Pascua, Miguel Angel; Muñoz Martín, Alfonso; Arcila, M.; Andeweg, Bernd
The orientation of the principal stresses and the principal stress difference ratio has been determined along the southwestern boundary of the Euroasiatic plate with Northamerican and African plates by inversion method of focal mechanisms of earthquakes. The ridge push (30~ to 65Q N) ranges from E-W to ESE-WSW, with R values that show a triaxial extensional stress. The state of stress changes to strike-slip regime in the transform fault zones, and the Shmax strike turns clockwise to NW in the dextral strike-slip faults and counterclockwise to the NE in the sinistral ones. Along the margin between the Euroasiatic-African plates, from the Azores triple junction to Algeria, Shmax keeps a constant NW-SE strike but the stress ratio values range from triaxial extensional stress state, to the West, to uniaxial compresive stress state, to the East, passing through a strike-slip regime in the middle zone. In this context and with a widely NWSE Shmax, strike-slip and extensional stresses prevail in most Iberian peninsula, whereas southwards it is dominated by uniaxial compresive stresses.
Dimensión fractal de la distribución espacial de fracturas en el área granítica de el Berrocal (Sistema Central): relación con el tensor de esfuerzos
(Revista de la Sociedad Geológica de España, 2000) Pérez López, Raúl; Muñoz Martín, Alfonso; Elorza Tenreiro, Francisco Javier; Paredes Bartolomé, Carlos; Vicente Muñoz, Gerardo de
En este trabajo se ha realizado un análisis del patrón de fracturación en el macizo granítico de El Berrocal mediante un análisis fractal a tres escalas diferentes (1:2.000, 1:10.000 y 1:500.000). El análisis se realizó en primer término para todo el conjunto de fracturas cartografiadas, y posteriormente con los mapas de fracturas filtrados mediante criterios dinámicos (sólo con las fracturas potencialmente activas bajo uno de los dos campos de paleoesfuerzos deducidos). La técnica empleada en el cálculo de la dimensión fractal fue el conteo binario de celdas bidimensional (box-counting 2-D) Y unidimensional (box-counting 1-D). Con esta última técnica se ha obtenido la variación de dimensión fractal con la orientación del perfil de fracturación analizado, que evidencia la existencia de una anisotropía fractal espacial de la fracturación en el caso de los mapas de fracturas asociados a los campos de paleoesfuerzos. La variación anisótropa de la fracturación muestra una dirección de máxima complejidad en el espaciado entre fracturas, reflejada en el valor máximo de dimensión fractal que es perpendicular a la orientación del máximo esfuerzo horizontal (σHmax). Por lo que respecta a las magnitudes de la dimensión fractal, ésta es mayor en el campo de paleoesfuerzos más reciente (Alpino), lo cual concuerda con que este campo de esfuerzos reactiva fallas previas y forma nuevas fallas, resultando un patrón de fracturación más complejo, y por tanto con mayor dimensión fractal. [ABSTRACT] A fractal analysis of fracture spatial patterns was carried out in the granitic massif of "El Berrocal" for three structural map scales (1:2.000, 1:10.000 and 1:500.000). At first, the total fracture map was analysed on each scale, and a second step, the dynarnic fracture maps were built and analysed by filtering of active faults due to two stress fields. The technique used to obtain the fractal dimension was the "box-counting" l-D and 2-D (one dimension and two dimension). The "box-counting l-D" technique has been used to take values of the fractal dimension related to the orientation of the measurements. One fractal anisotropy was showed in dynamic fracture maps associated to palaeostress fields, as the maximum value of fractal dimensiono A good relationship has been found between σHmax strike (maximum horizontal stress) and the orientation of the fracturing profiles for the maximum fractal dimension value. First results point to SHmax strike is perpendicular with the maximum complexity orientation. The larger value of fractal dimension in fracture dynarnic map due to recent stress field (Alpine) is agree with the fact that, this stress field activates old faults and generates new faults, and it shows a more complex fracture pattern.
Características de los tensores de esfuerzos activos entre la Dorsal Centroatlántica y la Península Ibérica.
(Geotemas, 2000) Vicente Muñoz, Gerardo de; Martín Velázquez, Silvia; Rodríguez Pascua, Miguel Angel; Muñoz Martín, Alfonso; Arcila, M.; Andeweg, Bernd
The orientation of the principal stresses and the principal stress difference ratio has been determined along the southwestern boundary of the Euroasiatic plate with Northamerican and African plates by inversion method of focal mechanisms of earthquakes. The ridge push (30~ to 65Q N) ranges from E-W to ESE-WSW, with R values that show a triaxial extensional stress. The state of stress changes to strike-slip regime in the transform fault zones, and the Shmax strike turns clockwise to NW in the dextral strike-slip faults and counterclockwise to the NE in the sinistral ones. Along the margin between the Euroasiatic-African plates, from the Azores triple junction to Algeria, Shmax keeps a constant NW-SE strike but the stress ratio values range from triaxial extensional stress state, to the West, to uniaxial compresive stress state, to the East, passing through a strike-slip regime in the middle zone. In this context and with a widely NWSE Shmax, strike-slip and extensional stresses prevail in most Iberian peninsula, whereas southwards it is dominated by uniaxial compresive stresses.