Investigation of active faults in Morocco using morphometric methods and drainage pattern analysis

A survey has been done of recently active faults in Morocco. In addition to field observations, morphometric methods were applied and an analysis was made of the drainage pattern. In the morphometric analysis, a map of vertical deformation was established from the elevations of summit level surfaces. This enables the recognition of neotectonic discontinuities and lithological contrasts; the actual discrimination of different rock-types can only be achieved by comparison with field observations. The analysis of drainage patterns — including their perturbations and anomalies — can also reveal the presence of features due to neotectonics, structural control or lithological variation. Certain faults can be detected which correspond to structures known from field geology or remote sensing (NE-SW and NW-SE oriented sets). Some new faults are observed which belong to these sets, as well as others which define a new N-S trending set. The present analysis leads to a distinction between ancient faults and currently active faults. The results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated.

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Zusammenfassung Bei einer Untersuchung der heute aktiven Störungen in Marokko wurden zusätzlich zu Feldbeobachtungen morphometrische Untersuchungen sowie eine Analyse des Entwässerungsnetzes durchgeführt. Bei der morphometrischen Analyse wurde eine Karte der vertikalen Deformationen von Aufragungen aus den Gipfelfluren abgeleitet. Dadurch können neotektonische Diskontinuitäten sowie lithologische Kontraste erkannt werden; die wirkliche Unterscheidung verschiedener Gesteinstypen kann aber nur im Vergleich mit Feldbeobachtungen erreicht werden. Die Analyse des Gewässernetzes — auch seiner Komplikationen und Anomalien — kann gleichfalls Elemente aufdecken, welche neotektonischen Ursprungs bzw. strukturell bedingt oder aber auf lithologische Unterschiede zurückzuführen sind. Bestimmte Störungen korrespondieren mit Strukturen, die aus der Feldgeologie oder der Fernerkundung bekannt sind (NE/ SW- und NW/SE-gerichtete Scharen). Einige neu entdeckte Störungen gehören zu diesen Scharen, während andere ein neues, N/S-streichendes System deutlich machen. Die vorgelegte Analyse erlaubt, zwischen älteren und noch heute aktiven Störungen zu unterscheiden. Unsere Ergebnisse sind in einer Karte der aktiven Störungen zusammengefaßt, in die die vertikalen Versätze gleichfalls eingetragen wurden.

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Résumé Un recensement des failles à jeu récent (néotectonique) a été fait sur l'ensemble du Maroc. Outre les observations de terrain, les méthodes de la morphométrie et celles de l'analyse du réseau hydrographique sont appliquées. En morphométrie, l'établissement d'une carte de la déformation verticale d'après la situation altimétrique de la surface sommitale permet la reconnaisance de structures (discontinuités) néotectoniques et d'alternances lithologiques (la discrimination ne peut être faite que sur le terrain). De même l'analyse du réseau hydrographique, de ses perturbations et de ses anomalies (cf. infra) met en évidence des discontinuités dues à la néotectonique, à la structure des terrains et à la lithologie. Les ensembles morphostructuraux marocains (Meseta, Rif, Atlas), ressortent nettement de la carte de synthèse. On y retrouve les failles connues par la géologie de terrain et par l'analyse des images satellitaires (ensembles de direction NE-SW et NW-SE), de nouvelles failles appartenant à ces deux familles, ainsi qu'un nouvel ensemble de failles de direction N-S. Cette analyse permet de distinguer failles actives et failles anciennes. Les résultats sont portés sur la carte des principales failles à jeu récent avec leurs rejets verticaux respectifs.

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Bulk sediment properties interpreted in light of qualitative and quantitative microfabric analysis

Sediments from Eckernförde Bay, Germany, are characterized by an aggregate and channel microstructure, with channel dimensions about two orders of magnitude larger than interparticle distances within aggregates. Porosity within aggregates as determined by image analysis of transmission electron micrographs was about 12% less than bulk porosity. Illite and smectite formed the bulk of most aggregates, while numerous biogenic particles generally occurred outside or on the periphery of aggregates. Microfabric analysis provides insights into permeability and consolidometer behavior of this sediment, reveals characteristics not apparent from bulk analyses, and may have implications for geochemistry and physical behavior of the sediment.     

DIAS—a novel technique for measuring in situ shear modulus

DIAS (duomorph in situ acquisition system) is an alternate technology requiring a single duomorph probe for measuring shear modulus in situ. The duomorph probe is a bending plate device that is vibrated and the resulting deflections measured using strain gauges. The ratio between the unconstrained bending of the duomorph in air and the constrained bending in sediment is a function of the sediment dynamic modulus from which shear modulus is calculated. This paper describes the theory underlying the DIAS system, the design of the system, the data reduction methods, and results from the initial deployment of the prototype system in Eckernförde Bay.     

From strike-slip faulting to oblique subduction: A survey of the Alpine Fault-Puysegur Trench transition,New Zealand,results of cruise Geodynz-sud leg 2

The Geodynz-sud cruise on board the R/V l'Atalante collected bathymetric, side-scan sonar and seismic reflection data along the obliquely convergent boundary between the Australian and Pacific plates southwest of the South Island, New Zealand. The survey area extended from 44°05 S to 49°40 S, covering the transition zone between the offshore extension of the Alpine Fault and the Puysegur Trench and Puysegur Ridge. Based on variations in the nature and structure of the crust on either side of the margin, the plate boundary zone can be divided into three domains with distinctive structural and sedimentary characteristics. The northern domain involves subduction of probably thinned continental crust of the southern Challenger Plateau beneath the continental crust of Fiordland. It is characterized by thick sediments on the downgoing slab and a steep continental slope disrupted by fault scarps and canyons. The middle domain marks the transition between subduction of likely continental and oceanic crust defined by a series of en echelon ridges on the downgoing slab. This domain is characterized by a large collapse terrace on the continental slope which appears to be due to the collision of the en echelon ridges with the plate margin. The southern domain involves subduction of oceanic crust beneath continental and oceanic crust. This domain is characterized by exposed fabric of seafloor spreading on the downgoing slab, a steep inner trench wall and linear ridges and valleys on the Puysegur ridge crest. The data collected on this cruise provide insights into the nature and history of both plates, and factors influencing the distribution of strike-slip and compressive strain and the evolution of subduction processes along a highly oblique convergent margin.     

Local Multiscale Approximations of Geostrophic Oceanic Flow: Theoretical Background and Aspects of Scientific Computing

In modern geoscience, understanding the climate depends on the information about the oceans. Covering two-thirds of the Earth, oceans play an important role. Oceanic phenomena are, for example: oceanic circulation; water exchanges between atmosphere, land, and ocean; or temporal changes of the total water volume. All these features require new methods in constructive approximation, since they are regionally bounded and not globally observable. This article deals with a new and alternative method of handling data with locally supported basis functions, modeling them in a multiscale scheme involving a wavelet approximation and presenting the main results for the dynamic topography and the geostrophic flow, e.g., in the Northern Atlantic. Further, it is demonstrated that compressional rates of the occurring wavelet transforms can be achieved by using of locally supported wavelets and investigating the signal distribution within different frequency bands.     

Contourite drift construction influenced by capture of Mediterranean Outflow Water deep-sea current by the Portimão submarine canyon (Gulf of Cadiz, South Portugal)

The margin of the Gulf of Cadiz is swept by the deep current formed by the Mediterranean Outflow Water (MOW) flowing from the Mediterranean to the Atlantic. On the northern margin of the Gulf (Algarve Margin, South Portugal), the MOW intensity is low and fine-grained contourite drifts are built up with an alongslope development. From new sedimentological data, this study emphasizes the presence of two types of contourite drifts separated only by a deep submarine canyon incising the slope with a north-south orientation (Portimão Canyon). High-resolution seismic and bathymetry interpretation shows that on the eastern side of the canyon, the MOW forms a thick and large detached drift (Albufeira Drift) prograding toward both north and west, as shown in seismic profiles, with a high sedimentation rate. On this side of the canyon, the MOW intensity is high enough to erode the slope forming a moat channel (Alvarez Cabral). On the western side of Portimão Canyon, the MOW energy is lower, preventing moat channel erosion. Only flat and thin drift develops (Portimão and Lagos Drifts) with slow aggradation and a low sedimentation rate. This difference in drift development is due to the presence of the canyon which generates an important change in hydrodynamic of the MOW, confirmed by temperature-density measurements showing that MOW flows down Portimão Canyon. The canyon is responsible for the deviation of the direction of the MOW as it partly catches the deep-sea current flowing westward (i.e. capture phenomenon). It creates, thus, a decrease of the flow energy, competency and capacity between the east and west sides of the canyon. Through this phenomenon of MOW deep-sea current capture, the canyon constitutes a morphologic feature generating an important change in the contourite deposition pattern.In addition to already known climatic and oceanographic influences, our results show the role of canyons on contourite drift building. This study provides new elements on autocyclic factors influencing the contourite sedimentation, which are important to consider in future sedimentary paleo-reconstruction interpretations.