Los riesgos geológicos y Ordenación Territorial

Existen amplias zonas del planeta en las que la incidencia de catástrofes naturales es muy elevada, especialmente en áreas con altas densidades de población y ocupación de espacios sometidos a riesgos naturales, la mayoría de los cuales tienen una filiación geológica clara. Por otra parte, la concienciación piública sobre estos fenómenos catastróficos naturales adquiere en la actualidad una dimensión añadida debido al papel preponderante desempeñado por los medios de comunicación, que muestran a todo el mundo, en cuestión de minutos, los efectos de estas catástrofes. Los ejemplos de los últimos grandes terremotos (Mejico, California y Japón), avalanchas, inundaciones, erupciones volcánicas, huracanes, etc, están presentes en la mente de todos.

Estratigrafía secuencial de sistemas deltaicos en cuencas de antepaís: ejemplos de Montserrat, Sant Llorenç del Munt, Montserrat y Roda (Paleogeno, cuenca de Antepaís surpirenaica).

After the sedimentological study of the Sant Llorenc del Munt, Montserrat and Roda deltaic systems, a stratigraphic subdivision based on three different scale transgressiveregressive sequences has been developed. This subdivision has been established on the coastal facies belts from the deduced shoreline (and associated facies belts) migration. These transgressive-regressive sequences are formed by a lower transgressive part with a deepening-upwards trend and a retrogradational staclung pattern and an upper regressive part, with shallowing-upwards trend and a progradational stacking pattern. The lowest scale sequences (metrical) have been named 'fundamental sequences'. A series of 'composite sequences', intermediate scale (decametric to hectometric), have been defined afier the study of the staclung pattem of the fundamental sequences. After the study of the stacking pattem of composite sequences there have been defined a series of large-scale (decametric to kilometric) 'composite megasequences'.

Los riesgos geológicos y Ordenación Territorial

Existen amplias zonas del planeta en las que la incidencia de catástrofes naturales es muy elevada, especialmente en áreas con altas densidades de población y ocupación de espacios sometidos a riesgos naturales, la mayoría de los cuales tienen una filiación geológica clara. Por otra parte, la concienciación piública sobre estos fenómenos catastróficos naturales adquiere en la actualidad una dimensión añadida debido al papel preponderante desempeñado por los medios de comunicación, que muestran a todo el mundo, en cuestión de minutos, los efectos de estas catástrofes. Los ejemplos de los últimos grandes terremotos (Mejico, California y Japón), avalanchas, inundaciones, erupciones volcánicas, huracanes, etc, están presentes en la mente de todos.

The Sottunga-Jurmo shear zone : structure and deformation history of a crustal-scale ductile shear zone in SW Finland

The aim of this study is to gain a better understanding of the structure and the deformation history of a NW-SE trending regional, crustal-scale shear structure in the Åland archipelago, SW Finland, called the Sottunga-Jurmo shear zone (SJSZ). Approaches involving e.g. structural geology, geochronology, geochemistry and metamorphic petrology were utilised in order to reconstruct the overall deformation history of the study area. The study therefore describes several features of the shear zone including structures, kinematics and lithologies within the study area, the ages of the different deformation phases (ductile to brittle) within the shear zone, as well as some geothermobarometric results. The results indicate that the SJSZ outlines a major crustal discontinuity between the extensively migmatized rocks NE of the shear zone and the unmigmatised, amphibolite facies rocks SW of the zone. The main SJSZ shows overall dextral lateral kinematics with a SW-side up vertical component and deformation partitioning into pure shear and simple shear dominated deformation styles that was intensified toward later stages of the deformation history. The deformation partitioning resulted in complex folding and refolding against the SW margin of the SJSZ, including conical and sheath folds, and in a formation of several minor strike-slip shear zones both parallel and conjugate to the main SJSZ in order to accommodate the regional transpressive stresses. Different deformation phases within the study area were dated by SIMS (zircon U-Pb), ID-TIMS (titanite U-Pb) and 40Ar/39Ar (pseudotachylyte wholerock) methods. The first deformation phase within the ca. 1.88 Ga rocks of the study area is dated at ca. 1.85 Ga, and the shear zone was reactivated twice within the ductile regime (at ca. 1.83 Ga and 1.79 Ga), during which the strain was successively increasingly partitioned into the main SJSZ and the minor shear zones. The age determinations suggest that the orogenic processes within the study area did not occur in a temporal continuum; instead, the metamorphic zircon rims and titanites show distinct, 10-20 Ma long breaks in deformation between phases of active deformation. The results of this study further imply slow cooling of the rocks through 600-700ºC so that at 1.79 Ga, 2 the temperature was still at least 600ºC. The highest recorded metamorphic pressures are 6.4-7.1 kbar. At the late stages or soon after the last ductile phase (ca. 1.79 Ga), relatively high-T mylonites and ultramylonites were formed, witnessing extreme deformation partitioning and high strain rates. After the rocks reached lower amphibolite facies to amphibolite-greenschist facies transitional conditions (ca. 500-550ºC), they cooled rapidly, probably due to crustal uplift and exhumation. The shear zone was reactivated at least once within the semi-brittle to brittle regime between ca. 1.79 Ga and 1.58 Ga, as evidenced by cataclasites and pseudotachylytes. In summary, the results of this study suggest that the Sottunga-Jurmo shear zone (and the South Finland shear zone) defines a major crustal discontinuity, and played a central role in accommodating the regional stresses during and after the Svecofennian orogeny.

Improved predictive mapping of indoor radon concentrations using ensemble regression trees based on automatic clustering of geological units.

PURPOSE: According to estimations around 230 people die as a result of radon exposure in Switzerland. This public health concern makes reliable indoor radon prediction and mapping methods necessary in order to improve risk communication to the public. The aim of this study was to develop an automated method to classify lithological units according to their radon characteristics and to develop mapping and predictive tools in order to improve local radon prediction. METHOD: About 240 000 indoor radon concentration (IRC) measurements in about 150 000 buildings were available for our analysis. The automated classification of lithological units was based on k-medoids clustering via pair-wise Kolmogorov distances between IRC distributions of lithological units. For IRC mapping and prediction we used random forests and Bayesian additive regression trees (BART). RESULTS: The automated classification groups lithological units well in terms of their IRC characteristics. Especially the IRC differences in metamorphic rocks like gneiss are well revealed by this method. The maps produced by random forests soundly represent the regional difference of IRCs in Switzerland and improve the spatial detail compared to existing approaches. We could explain 33% of the variations in IRC data with random forests. Additionally, the influence of a variable evaluated by random forests shows that building characteristics are less important predictors for IRCs than spatial/geological influences. BART could explain 29% of IRC variability and produced maps that indicate the prediction uncertainty. CONCLUSION: Ensemble regression trees are a powerful tool to model and understand the multidimensional influences on IRCs. Automatic clustering of lithological units complements this method by facilitating the interpretation of radon properties of rock types. This study provides an important element for radon risk communication. Future approaches should consider taking into account further variables like soil gas radon measurements as well as more detailed geological information.

El margen continental catalan (I): el marco de la cuenca Catalano-Balear

El presente primer número y los dos siguientes del volumen 29 de Acta Geologica Hispanica, forman parte de un conjunto temático dedicado a los avances en el estudio del margen continental catalán (NE de Iberia). Estos números especiales tienen por objeto recoger algunas de las contribuciones generales o regionales realizadas sobre este tema por varios equipos de trabajo de distintas disciplinas y especialidades, cuya actividad se ha venido desarrollando en el marco de numerosos proyectos de investigación nacionales e internacionales o bien dentro del desempeño de su actividad profesional. La investigación geológica y geofísica en la cuenca Catalano-Balear, con el margen continental catalán formando parte de su borde nordoccidental, ha sido muy intensa debido al interés petrolífero de esta zona...

Sedimentology and Stratigraphy of the Pleistocene sediments in Lake Llauset (Southern Pyrenees, Spain)-a first approach

The high alpine valleys in the Southem Pyrenees are characterised by a many small lakes and ponds. They occur above 2000 m and are said to have been formed by glacial erosion. The sediments in these basins should, therefore, contain s t p tigraphic information since deglaciation, at least. An interesting and may be one of the most important of these basins is Lake Llauset in the Alta Ribagorca. The Llauset basin has recently been developped for hydsopower production. In conection with the construction of the retaining wall at the 'Riegel' the sedimentary filling of the lake basin could be investigated, and the first sedimentological and stratigraphicalresults are presented.

Estudio petrológico de las rocas volcánicas del Pérmico de Gréixer (Pirineo catalán)

Se presenta un estudio sobre las rocas volcánicas de edad permica que afloran extensamente cerca de Greker. a lo largo del borde de la Zona Axial pirenaica. El estudio al microscopio y los análisis quimicos de las muestras recogidas, junto con los datos de campo, han proporcionado nuevos resultados sobre la datación y génesis de estas rocas, y sobre sus relaciones en el marco geológico regional y su evolución. Se pone de relieve la muy notable proporción de las ignimbritas en el material volcánico objeto de este estudio. Igualmente, la predominante composición peralcalina de este material. Las hipótesis que pueden explicar tal composición son discutidas.

Estratigrafia del Cretacico inferior continental de la Cordillera Iberica Central

El Cretácico inferior continental de la Cordillera Ibérica Central está representado en dos subcuencas de sedimentación: las Cubetas de Aguilón y Oliete. Los estudios realizados sobre estos materiales han permitido definir nuevas unidades litoestratigráficas, cuya caracterización bioestratigráfica se realiza a partir de su contenido en carofitas. La identificación de discontinuidades significativas permiten definir tres secuencias de depósito que abarca en el intervalo temporal Valanguniense y/o Hauteriviense-Barremiense inferior y que son correlacionables con las S.D.K1.2 y/o K1.3, K1.4 YK1.5 y/o K1.6 definidas en Salas et al. (1991) y Salas y Casas (1993) para la Cuenca del Maestrazgo. Estos resultados ponen de manifiesto que el registro estratigráfico de la zona central de la Cordillera Ibérica tiene una entidad similar al de los márgenes de las Cuencas del Maestrazgo, Aliaga- Peñagolosa y Cameros.

A reappraisal of 'International Stratigraphic Lexicon' and the need for the creation named units critical catalogues

Analysis of stratigraphic terminology and classification, shows that time-related stratigraphic units, which by definition have a global extent, are the concern of international cornrnissions and committees of the intemational Union of Geological Sciences (IUGS) . In contrast, lithostratigraphic, and other closely related units, are regional in extent and are catalogued in the International Stratigraphic Lexicon (ISL), the last volume of which, was published in 1987. Tlie intemational Commission on Stratigraphy (ICS) is currently attempting to revitalize the publication of ISL, given that the information contained in published volumes has never been updated, and that there has been a significant increase in stratigraphic research in recent decades. The proliferation of named units in the South Pyrenean and Ebro Basin Paleogene is evaluated to illustrate the extent of the problem. Moreover, new approaches to stratigraphic analysis have led to the naming of genetic units according to similar guidelines followed in the naming of descnptive or lithostratigraphic units. This has led to considerable confusion. The proposal to revitalize the ISL is accepted as part of the solution, that should also include the publication of critica1 catalogues, and the creation of norms for genetic unit terminology.

Análisis microestructural de los afloramientos en las calizas cretácicas del macizo del Garraf (prov. de Barcelona, España)

LA aplicación del modelo de la 'deformación discontinua' propuesto pr F. ARTHAUD y M. MATTAUER al análisis de la tectónica frágil de dos canteras del macizo de Garraf (prov. de Barceona, España), permite diferenciar las microestructuras pertenecientes a dos deformaciones distintas ('compresión' y 'distendión·) y caracterizar las direcciones principales de deformación para cada una de ellas.

Precisiones acerca de la significación petrológica y estructural de las rocas gneísicas y cataclásticas del Maresme (prov. de Barcelona)

Se estudian pequeños afloramientos de rocas metamórficas y cataclásticas ubicadas en el granito herciniano de la Cadena Costera Catalana al NE de Barcelona. Tras una breve íntesis de las diversas ideas emitidas sobre la génesis de estas rocas se realiza un estudio comparativo de las mismas. De él se infiere la presencia de dos grupos de rocas de significación petrogenética y tectónica distinta: 1) Los gneises de Mataró, que resultan del metamorfismo polifísico progresivo herciniano de sedimentos del Paleozoico inferior y 2) las rocas cataclásticas de Caldetes, ligadas a deformaciones internas en el batolito del granito herciniano postectónico, acompañadas de transformaciones hidrotermales en mayor o menor grado.

Rockfall susceptibility assessment and remote geological mapping with LiDAR point clouds

Characterizing the geological features and structures in three dimensions over inaccessible rock cliffs is needed to assess natural hazards such as rockfalls and rockslides and also to perform investigations aimed at mapping geological contacts and building stratigraphy and fold models. Indeed, the detailed 3D data, such as LiDAR point clouds, allow to study accurately the hazard processes and the structure of geologic features, in particular in vertical and overhanging rock slopes. Thus, 3D geological models have a great potential of being applied to a wide range of geological investigations both in research and applied geology projects, such as mines, tunnels and reservoirs. Recent development of ground-based remote sensing techniques (LiDAR, photogrammetry and multispectral / hyperspectral images) are revolutionizing the acquisition of morphological and geological information. As a consequence, there is a great potential for improving the modeling of geological bodies as well as failure mechanisms and stability conditions by integrating detailed remote data. During the past ten years several large rockfall events occurred along important transportation corridors where millions of people travel every year (Switzerland: Gotthard motorway and railway; Canada: Sea to sky highway between Vancouver and Whistler). These events show that there is still a lack of knowledge concerning the detection of potential rockfalls, making mountain residential settlements and roads highly risky. It is necessary to understand the main factors that destabilize rocky outcrops even if inventories are lacking and if no clear morphological evidences of rockfall activity are observed. In order to increase the possibilities of forecasting potential future landslides, it is crucial to understand the evolution of rock slope stability. Defining the areas theoretically most prone to rockfalls can be particularly useful to simulate trajectory profiles and to generate hazard maps, which are the basis for land use planning in mountainous regions. The most important questions to address in order to assess rockfall hazard are: Where are the most probable sources for future rockfalls located? What are the frequencies of occurrence of these rockfalls? I characterized the fracturing patterns in the field and with LiDAR point clouds. Afterwards, I developed a model to compute the failure mechanisms on terrestrial point clouds in order to assess the susceptibility to rockfalls at the cliff scale. Similar procedures were already available to evaluate the susceptibility to rockfalls based on aerial digital elevation models. This new model gives the possibility to detect the most susceptible rockfall sources with unprecented detail in the vertical and overhanging areas. The results of the computation of the most probable rockfall source areas in granitic cliffs of Yosemite Valley and Mont-Blanc massif were then compared to the inventoried rockfall events to validate the calculation methods. Yosemite Valley was chosen as a test area because it has a particularly strong rockfall activity (about one rockfall every week) which leads to a high rockfall hazard. The west face of the Dru was also chosen for the relevant rockfall activity and especially because it was affected by some of the largest rockfalls that occurred in the Alps during the last 10 years. Moreover, both areas were suitable because of their huge vertical and overhanging cliffs that are difficult to study with classical methods. Limit equilibrium models have been applied to several case studies to evaluate the effects of different parameters on the stability of rockslope areas. The impact of the degradation of rockbridges on the stability of large compartments in the west face of the Dru was assessed using finite element modeling. In particular I conducted a back-analysis of the large rockfall event of 2005 (265'000 m3) by integrating field observations of joint conditions, characteristics of fracturing pattern and results of geomechanical tests on the intact rock. These analyses improved our understanding of the factors that influence the stability of rock compartments and were used to define the most probable future rockfall volumes at the Dru. Terrestrial laser scanning point clouds were also successfully employed to perform geological mapping in 3D, using the intensity of the backscattered signal. Another technique to obtain vertical geological maps is combining triangulated TLS mesh with 2D geological maps. At El Capitan (Yosemite Valley) we built a georeferenced vertical map of the main plutonio rocks that was used to investigate the reasons for preferential rockwall retreat rate. Additional efforts to characterize the erosion rate were made at Monte Generoso (Ticino, southern Switzerland) where I attempted to improve the estimation of long term erosion by taking into account also the volumes of the unstable rock compartments. Eventually, the following points summarize the main out puts of my research: The new model to compute the failure mechanisms and the rockfall susceptibility with 3D point clouds allows to define accurately the most probable rockfall source areas at the cliff scale. The analysis of the rockbridges at the Dru shows the potential of integrating detailed measurements of the fractures in geomechanical models of rockmass stability. The correction of the LiDAR intensity signal gives the possibility to classify a point cloud according to the rock type and then use this information to model complex geologic structures. The integration of these results, on rockmass fracturing and composition, with existing methods can improve rockfall hazard assessments and enhance the interpretation of the evolution of steep rockslopes. -- La caractérisation de la géologie en 3D pour des parois rocheuses inaccessibles est une étape nécessaire pour évaluer les dangers naturels tels que chutes de blocs et glissements rocheux, mais aussi pour réaliser des modèles stratigraphiques ou de structures plissées. Les modèles géologiques 3D ont un grand potentiel pour être appliqués dans une vaste gamme de travaux géologiques dans le domaine de la recherche, mais aussi dans des projets appliqués comme les mines, les tunnels ou les réservoirs. Les développements récents des outils de télédétection terrestre (LiDAR, photogrammétrie et imagerie multispectrale / hyperspectrale) sont en train de révolutionner l'acquisition d'informations géomorphologiques et géologiques. Par conséquence, il y a un grand potentiel d'amélioration pour la modélisation d'objets géologiques, ainsi que des mécanismes de rupture et des conditions de stabilité, en intégrant des données détaillées acquises à distance. Pour augmenter les possibilités de prévoir les éboulements futurs, il est fondamental de comprendre l'évolution actuelle de la stabilité des parois rocheuses. Définir les zones qui sont théoriquement plus propices aux chutes de blocs peut être très utile pour simuler les trajectoires de propagation des blocs et pour réaliser des cartes de danger, qui constituent la base de l'aménagement du territoire dans les régions de montagne. Les questions plus importantes à résoudre pour estimer le danger de chutes de blocs sont : Où se situent les sources plus probables pour les chutes de blocs et éboulement futurs ? Avec quelle fréquence vont se produire ces événements ? Donc, j'ai caractérisé les réseaux de fractures sur le terrain et avec des nuages de points LiDAR. Ensuite, j'ai développé un modèle pour calculer les mécanismes de rupture directement sur les nuages de points pour pouvoir évaluer la susceptibilité au déclenchement de chutes de blocs à l'échelle de la paroi. Les zones sources de chutes de blocs les plus probables dans les parois granitiques de la vallée de Yosemite et du massif du Mont-Blanc ont été calculées et ensuite comparés aux inventaires des événements pour vérifier les méthodes. Des modèles d'équilibre limite ont été appliqués à plusieurs cas d'études pour évaluer les effets de différents paramètres sur la stabilité des parois. L'impact de la dégradation des ponts rocheux sur la stabilité de grands compartiments de roche dans la paroi ouest du Petit Dru a été évalué en utilisant la modélisation par éléments finis. En particulier j'ai analysé le grand éboulement de 2005 (265'000 m3), qui a emporté l'entier du pilier sud-ouest. Dans le modèle j'ai intégré des observations des conditions des joints, les caractéristiques du réseau de fractures et les résultats de tests géoméchaniques sur la roche intacte. Ces analyses ont amélioré l'estimation des paramètres qui influencent la stabilité des compartiments rocheux et ont servi pour définir des volumes probables pour des éboulements futurs. Les nuages de points obtenus avec le scanner laser terrestre ont été utilisés avec succès aussi pour produire des cartes géologiques en 3D, en utilisant l'intensité du signal réfléchi. Une autre technique pour obtenir des cartes géologiques des zones verticales consiste à combiner un maillage LiDAR avec une carte géologique en 2D. A El Capitan (Yosemite Valley) nous avons pu géoréferencer une carte verticale des principales roches plutoniques que j'ai utilisé ensuite pour étudier les raisons d'une érosion préférentielle de certaines zones de la paroi. D'autres efforts pour quantifier le taux d'érosion ont été effectués au Monte Generoso (Ticino, Suisse) où j'ai essayé d'améliorer l'estimation de l'érosion au long terme en prenant en compte les volumes des compartiments rocheux instables. L'intégration de ces résultats, sur la fracturation et la composition de l'amas rocheux, avec les méthodes existantes permet d'améliorer la prise en compte de l'aléa chute de pierres et éboulements et augmente les possibilités d'interprétation de l'évolution des parois rocheuses.