A strike‐slip core complex from the Najd fault system,Arabian shield

Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal‐scale strike‐slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal‐scale vertical strike‐slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike‐slip fault zone, and the segments were separated by another 30 km of lateral motion. Strike‐slip core complexes like the Qazaz Dome may be common and may have an important local effect on crustal strength.     

Tutorial: unified 1D inversion of the acoustic reflection response

Acoustic inversion in one-dimension gives impedance as a function of travel time. Inverting the reflection response is a linear problem. Recursive methods, from top to bottom or vice versa, are known and use a fundamental wave field that is computed from the reflection response. An integral over the solution to the Marchenko equation, on the other hand, retrieves the impedance at any vertical travel time instant. It is a non-recursive method, but requires the zero-frequency value of the reflection response. These methods use the same fundamental wave field in different ways. Combining the two methods leads to a non-recursive scheme that works with finite-frequency bandwidth. This can be used for target-oriented inversion. When a reflection response is available along a line over a horizontally layered medium, the thickness and wave velocity of any layer can be obtained together with the velocity of an adjacent layer and the density ratio of the two layers. Statistical analysis over 1000 noise realizations shows that the forward recursive method and the Marchenko-type method perform well on computed noisy data.     

Improving the performance of genetic algorithms for land-use allocation problems

Multi-objective optimization can be used to solve land-use allocation problems involving multiple conflicting objectives. In this paper, we show how genetic algorithms can be improved in order to effectively and efficiently solve multi-objective land-use allocation problems. Our focus lies on improving crossover and mutation operators of the genetic algorithms. We tested a range of different approaches either based on the literature or proposed for the first time. We applied them to a land-use allocation problem in Switzerland including two conflicting objectives: ensuring compact urban development and reducing the loss of agricultural productivity. We compared all approaches by calculating hypervolumes and by analysing the spread of the produced non-dominated fronts. Our results suggest that a combination of different mutation operators, of which at least one includes spatial heuristics, can help to find well-distributed fronts of non-dominated solutions. The tested modified crossover operators did not significantly improve the results. These findings provide a benchmark for multi-objective optimization of land-use allocation problems with promising prospectives for solving complex spatial planning problems.     

A simple model of seasonal open ocean convection

 Aspects of open ocean deep convection variability are explored with a two-box model. In order to place the model in a region of parameter space relevant to the real ocean, it is fitted to observational data from the Labrador Sea. A systematic fit to OWS Bravo data allows us to determine the model parameters and to locate the position of the Labrador Sea on a stability diagram. The model suggests that the Labrador Sea is in a bistable regime where winter convection can be either “on” or “off ”, with both these possibilities being stable climate states. When shifting the surface buoyancy forcing slightly to warmer or fresher conditions, the only steady solution is one without winter convection.  We then introduce short-term variability by adding a noise term to the surface temperature forcing, turning the box model into a stochastic climate model. The surface forcing anomalies generated in this way induce jumps between the two model states. These state transitions occur on the interannual to decadal time scale. Changing the average surface forcing towards more buoyant conditions lowers the frequency of convection. However, convection becomes more frequent with stronger variability in the surface forcing. As part of the natural variability, there is a non-negligible probability for decadal interruptions of convection. The results highlight the role of surface forcing variability for the persistence of convection in the ocean.     

Water use by intensively cultivated willow using estimated stomatal parameter values

Large land areas in Sweden are planned to be planted with high producing, short rotation forest stands of willow in the beginning of the 1990s. Since willow is a highly hydrophilic species, this new land use may have strong implications on water resources. To assess these implications, evaporation of Salix viminalis and Salix viminalis x caprea stands in lysimeters was analysed with the simple, yet physically realistic KAUSHA model. Parameter values for the Lohammar equation were deduced (b = 100 m³ kg^?1, k_max = 0.01 m s^?1), believed to be applicable to other sites. Simulated evaporation during the 1980 growth season for a normal stand with a production of 12 tonnes of dry matter per hectare per season was 526 mm, of which 375 mm was transpiration, 56 mm interception evaporation, and 95 mm soil evaporation. For an optimally irrigated 20-tonnes stand, the total evaporation was 584 mm, of which 430 mm was transpiration. As a comparison, Penman open water evaporation was 430 mm. To avoid soil water stress in the 20-tonnes stand, 140 mm was needed as irrigation, equivalent to 25 per cent of the mean annual precipitation. Since intensively cultivated willow plantations seemed to be using much water, it was concluded that introduction of this agri-forestry practice must be carefully planned to make use of this property, e.g. in biological filters or in reclaiming water-logged land.     

A device for rapid sectioning of soft bottom sediment cores

A new mechanical sectioning device for transverse cutting of cylindrical soft bottom sediment cores is presented. The instrument is rapid and efficient in use, works serially when sectioning a core and permits rinsing of the sample compartment without removal from the coring tube. The device is made of plastic, is lightweight, convenient to operate even in the field and simple and cheap to manufacture.     

Petrogenesis of Archaean Tonalites

The Archean tonalitic magma series is characterized by a high Al₂O₃ and Na₂O content. Tertiary tonalites with similar major element composition have been generated in subduction zones. It is therefore suggested that the Archean tonalites was generated in relation to subduction zones, the primary magma of the series being of dioritic composition. The generation of the primary magma occurred at about 15 kbar, while the recent generation of andesite occur at about 30 kbar. The higher frequency of generation in the Archean, and the relatively small depth of geneeration is related to the slightly higher temperatures of the mantle in the Archean.

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Zusammenfassung Die tonalitische Magmenfolge des Archäikum wird durch hohe Al₂O₃- und Na₂O-Gehalte gekennzeichnet. Tertiäraltrige Tonalite mit ähnlicher Hauptelement-Zusammensetzung entstanden in Subduktionszonen. Deshalb wird vorgeschlagen, daß die archäischen Tonalite im Zusammenhang mit Subduktionszonen entstanden, wobei das primäre Magma der Folge dioritischer Zusammensetzung war. Das primäre Magma entstand unter einem Druck von etwa 15 kbar; in jüngster Zeit entsteht aber Andesit bei etwa 30 kbar. Die höhere Entstehungsrate im Archäikum wird, so wie auch die verhältnismäßig geringe Entstehungstiefe, zu den etwas höheren Manteltemperaturen im Archäikum in Beziehung gesetzt.

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Résumé La série des magmas tonalitiques de l'Archéen est caractérisée par une haute teneur en Al₂O₃. Les tonalites tertiaires, de même composition quant aux éléments majeurs, ont été engendrées dans des zones de subduction. C'est pourquoi il est suggéré que les tonalites archéennes aient été engendrées en relation avec des zones de subduction, le magma primaire de la série étant de composition dioritique. La genèse du magma primaire se fit sous environ 15 kbar, tandis que la genèse récente des andésites se fait à 30 kbar. La fréquence élevée de la formation dans l'Archéen et la profondeur relativement faible de cette formation est en liaison avec les températures légèrement plus élevées du manteau dans l'Archéen.

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Assessing hydrological changes in a regulated river system over the last 90 years in Rimac Basin (Peru)

Theoretical and Applied Climatology - Hydrological changes were assessed considering possible changes in precipitation and regulation or hydraulic diversion projects developed in the basin since...     

The Changing Location of Service Activities in the Copenhagen Region

Geografisk Tidsskrift, Danish Journal of Geography 97: 120–131, 1997.

The location of services in the Copenhagen region is described and analyzed. Six types of services are distinguished:

Local private and public services, serving the daily needs of the population, e.g. retailing, have suburbanized, closely following the distribution of population, though with a time-lag. The same goes for services which serve more special needs, e, g, hospitals.

Among producer services, some remain in the centre of Copenhagen, e.g. lawyer firms, partly for historical reasons, partly to minimize costs of face-to-face contacts with business partners. But contrary to traditional theory, most producer services are suburbanizing, mainly in order to find large sites and to improve their accessibility for cars. Some have shifted to the western suburbs to reduce costs (back offices) or to be close to the traffic arteries which connect Copenhagen with the rest of Denmark (wholesaling). Business services, e.g. engineering consultants, have primarily moved to the northern, amenity-rich suburbs, for reasons of prestige and of proximity to their high-status labour force. Still other services have located in a more hap-hazard way where they could find large areas, e.g. the airport and military establishments.