ALBERT

Description: The boundary between the American and European plates emerges in Iceland, an outstanding natural laboratory where it is possible to analyse ongoing rifting processes. In the North Volcanic Zone, we studied with unprecedented detail an active rift, known as the Theistareykir Fissure Swarm (ThFS). We surveyed an area of 85 km2 with 694 measurement sites along 1537 post-Late Glacial Maximum extension fractures. In the southern sector of the study area, fractures strike N30–40° with opening directions about N120°. Fractures in the central sector strike about N00° and opening directions are N90–100°. In the northern sector, fractures strike about N30° with opening directions about N125°. Through a comparison with older faults cropping out in the substrate at the shoulder of the ThFS, we are able to suggest that variations in fracture strike are the effect of substrate structural inheritance as well as the possible interaction with the Tjörnes Fracture Zone. With regard to kinematics, we highlight that most fractures show a small, but systematic, strike-slip component (a more frequent right-lateral component and a less common, left-lateral one). This cannot be explained as the result of fracture strike rotation relative to the regional, tectonic least principal stress. We conclude that the net opening directions can result from the combination of tectonic offsets and events caused by shallow magma chamber inflation and/or dyke intrusions. The latter can produce transcurrent components of displacement along new or already existing fractures.

Description: This study investigated photosynthetic and oxidative stress-related responses to moderate (500 μmol photons m −2 s −1 ) and high irradiances (1500 μmol photons m −2 s −1 ) in two tropical intertidal seagrasses, Halophila ovalis and Thalassia hemprichii . Exposure to high irradiance for 3 h resulted in a large decline in the maximum quantum yield of photosystem II (Fv/Fm) and in the effective quantum yield of photosystem II (ΦPSII) but induced non-photochemical quenching (NPQ) and chloroplast clumping in H. ovalis . Thalassia hemprichii , however, showed only a minor decrease in Fv/Fm and ΦPSII, and no change in either NPQ or the intracellular arrangement of chloroplasts. The irradiance did not affect reactive oxygen species (ROS) or superoxide dismutase (SOD) activity in either seagrass, whereas high irradiance enhanced ascorbate peroxidase (APX) activity in H. ovalis . The results from a subsequent experiment using an oxidative stress inducer, methyl viologen (MV), also showed a higher degree of Fv/Fm inhibition in H. ovalis . These results show that H. ovalis is much more physiologically responsive to high irradiances and oxidative stress than T. hemprichii and that its photoprotective mechanisms involve NPQ, APX and reduction of the amount of light absorbed through the clumping of its chloroplasts.

Description: Vibrios are rod-shaped bacteria, and are a functionally and phylogenetically diverse grouping of Gram-negative microbes found widely in aquatic, estuarine, and marine habitats. Approximately a dozen Vibrio species are known to cause disease in humans, and infection is usually initiated from exposure to seawater or consumption of raw or undercooked seafood. Although a wide range of different bacterial species contain multiple chromosomes, Vibrio species are noted in that they possess two circular chromosomes. Bacteria of the genus Vibrio are commonly found in tropical and temperate coastal and estuarine waters. Vibrios are among the most common bacteria that inhabit surface waters throughout the world and are responsible for a number of severe infections both in humans and animals. Vibriosis is characterized by diarrhea, primary septicemia, wound infections, or other extraintestinal infections. Select strains of V. cholerae, V. parahaemolyticus, V. vulnificus, and V. alginolyticus are perhaps considered the most serious human pathogens from this genus. Two Vibrio species in particular, V. vulnificus and V. parahaemolyticus are significant foodborne human pathogens, and most frequently infections occur via the consumption of naturally contaminated shellfish produce. It is worth noting that these pathogens represent a significant cause of morbidity and mortality. For example, an estimated 80,000 people contract Vibrio infections each year in the United States, with a sizeable fraction originating from foodborne sources, such as consumption of raw or undercooked seafood produce. Recent data from the Centers for Disease Control and Prevention (CDC) in the United States have indicated that there has been a significant increase in reported infections associated with vibrios, particularly in the last two decades. The annual incidence of reported vibriosis per 100,000 population has increased significantly in the United States from 1996 to 2010, highlighting the importance of these pathogens from a clinical context. Calculations based upon probable incidence of vibriosis have estimated that V. vulnificus and V. parahaemolyticus are the first and third most costly marine-borne pathogens, costing $233 and $20 million, respectively. From a foodborne perspective V. vulnificus and V. parahaemolyticus represent the major pathogens from the Vibrio genus in terms of clinical impact and relevance, and as such this chapter is mostly concerned with these species. These taxa do not sustain prolonged presence in clinical or agricultural settings, where it would likely undergo human-induced selection for antibiotic resistance. As such, these bacteria represent a particularly interesting group of pathogens to study antibiotic resistance, as they provide a “snapshot” of resistance presumably acquired from environmental rather than clinical settings. Despite their public-health significance, strains of V. parahaemolyticus and V. vulnificus have not been extensively monitored for antimicrobial resistance, in contrast to enteric pathogens such as Salmonella or Campylobacter. Given their increasing incidence, global distribution, and severity of disease progression (especially V. vulnificus) it is critical to gain a better understanding of the antimicrobial susceptibility patterns of V. vulnificus and V. parahaemolyticus originating from the environment (Shaw et al., 2014). Data from such sources is invaluable, particularly from routine antimicrobial screening of large numbers of environmental and clinical Vibrio strains as it can provide effective baseline data for treatment purposes.

Description: Most seals (pinnipeds) disperse from centralised terrestrial haul out sites to forage at sea which results in great intraspecific competition for prey. This competition may be reduced by gender-specific differences in depth use, something which should be enhanced by sexual dimorphism because diving ability is a function of body size. This thesis discusses the sex-specific behaviour of harbour seals (Phoca vitulina) in the North Sea. The aim was to determine the extent to which this species might have gender-dependent foraging strategies and, where apparent, to identify possible causes. The diving behaviour of six males and six females was analysed using animal-attatched data loggers (dead reckoners). With a weight of 73 kg (SD = 10) the equipped males were approx. 30 % heavier than females at 55 kg (SD = 8). All seals spent most of their time at sea (males 75.8 %, females 88.1 %) and perfmmed mainly U-shaped dives (ea. 80 %). The maximum recorded dive depth was 43 m for the males and 28 m for the females. Maximum dive duration lasted to 10 minuntes for females and 16 minutes for males. Mean trip duration was 44.1 h (SD = 65.5) for males and 46.8 h for females (SD = 35). Both genders showed significant correlations between dive duration and dive depth, as well as the durations of the descent, bottom and ascent phase and dive depth. However, there were no significant differences either in diving capabilities or in the foraging efficiency of the two sexes. An effect of body size on the diving capabilities of the seals could not been demonstrated. This indicates that the seals' diving capabilities in the North Sea are mainly determined by the bathymetry. Possible sex-specific differences might not be revealed because the seals do not reach their physiological limits in the shallow North Sea. Also, the large variance in the data as well as the small sample size mad it difficult to identify gender-specific differences. Tests of statistical power reveal that data from a total of 262 seals would be needed as an adequate sample size to determine with any certainty whether inter-sex differences occur.

Description: We explore a parameterization for mesoscale turbulence, closely related to that of Gent and McWilliams, in which forcing terms proportional to the isopycnal flux of potential vorticity appear in the averaged momentum equations. We show that in the presence of variable bottom topography, the parameterization predicts alongslope mean flow and a corresponding upslope bolus (eddy) flux of tracer that is associated with an alongslope-directed bottom eddy stress. The upslope bolus flux is in qualitative agreement with observations of a cold dome over seamounts. The predicted alongslope flow corresponds to flow fields found in geostrophic turbulence experiments and has some similarity (although conceptually very different, as discussed in the text) to Holloway's prediction based on statistical mechanics. By considering continuous stratification as a limiting case of a multilayer model, we show how to treat the surface and bottom boundaries. Practical application of the parameterization is illustrated using a three-dimensional -coordinate ocean circulation model that is very similar to the Bryan–Cox–Semtner model. The model-computed flow is consistent with observations of anticyclonic flow around a seamount. We show that the bottom eddy stress associated with the parameterization can be large, even compared to the annual mean surface wind stress, and hence could have important implications for the biology and water mass distribution of the coastal ocean as well as for the large-scale ocean circulation. From the climate modelling perspective, the approach adopted here provides a single formalism that combines the advantages of the Gent and McWilliams parameterization with alongslope mean flow similar to that suggested by Holloway.

Description: Herbivory can modify seaweed community structure by affecting variation in the abundance and distribution over spatial and temporal scales. To deter herbivores, seaweeds have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by environmental factors such as nutrient availability. In two sets of experiments 5 red, 4 brown, and 1 green seaweeds were tested for inducible defenses following exposure to direct consumption by an amphipod community. In addition, the effects of consumer presence and neighborhood grazing (indirect consumption) on the induction of defenses were examined in the red seaweed Gracilaria cearensis and the green seaweed Codium decorticatum under natural and additionally 100% elevated nutrient levels for C. decorticatum. In preliminary studies, suitable organisms for the induction experiments were determined in testing survival of potential tropical algae from the Brazilian littoral under laboratory conditions and performing multiple-choice feeding assays for four important Brazilian herbivore species in order to determine their preference rankings of these algae. The amphipod community dominated by Elasmopus brasiliensis was identified as the most suitable grazers. Induction of defense was evaluated after consumer exposure in choice-feeding experiments by offering live algae (LA, total defense) and reconstituted food (RF, chemical defense) of previously consumed (treated) and unconsumed algae (control). Nutrient enrichment did not affect induction of defense in C. decorticatum, yet unfertilized seaweeds were more palatable relatively to fertilized conspecifics. Different consumer activities did not affect palatability in G. cearensis, yet C. decorticatum seemed to induce resistance (LA) after reception of waterbome cues from consumed conspecifics. Unexpectedly C. decorticatum RF exhibited higher susceptibility to amphipods after consumer exposure in both experiments performed. While no significant decrease in palatability was observed in previously consumed algae compared to unconsumed controls after one week, two red seaweeds, Chondrophycus flagellifera (RF) and Pterocladiella capillacea (LA), exhibited significantly reduced palatability after consumer exposure. The brown seaweed Lobophora variegata showed significantly retarded chemical resistance after three weeks. This is the first report of inducible chemical defense in a red seaweed.

Description: Die "höheren" Caenogastropoden umfassen viele tausend rezente und fossile Arten. Ihre charakteristischen Gehäuse haben gewöhnlich einen hohen Wiedererkennungswert, sind häufige Elemente fossiler Ablagerungen und eröffnen damit ausgezeichnete Möglichkeiten neontologische und paläontogische Studien zu korrelieren. Das Ziel solcher Studien ist hier, Evolution nachzuzeichnen, um sie dann auch interpretieren und letztlich verstehen zu können. Es wurde ein tendenziell holistischer Arbeitsansatz gewählt, der die Synthese gehäusemorphologischer, anatomischer, molekulargenetischer, reproduktionsbiologischer, ökologischer und biogeographischer Daten in die zeitliche Dimension übersetzt und damit in den Kontext der Geodynamik stellt. Diese Vorgehensweise wird als paläobiologische Konzeption bezeichnet. Im Ergebnis stehen folgende Erkenntnisse und darauf basierende Maßnahmen: die "höheren" Caenogastropoda sind sehr wahrscheinlich monophyletisch und werden als Überordnung Latrogastropoda nov klassifiziert. Die Ordnung Neomesogastropoda ist paraphyletisch und Teile von ihnen repräsentieren die Stammgruppe der Ordnung Neogastropoda. Es zeigt sich, daß viele der neontologisch klar zu definierenden evolutiven Linien, ohne weitere paläontologische Studien, im systematischen Vakuum wurzeln. Die stammesgeschichtlichen Lücken können nun anhand von Merkmalsabgrenzung - nach "unten" und nach "oben" - definiert bzw abstrahiert werden und als Phantombilder für zukünftige Recherchen dienen. Auf Grundlage der phylogenetischen Analysen wurde eine weitreichende Revison der Klassifikation erforderlich und durchgeführt. Der Ursprung der Latrogastropoda nov könnte in einer Lime liegen, welche auch zu der Stammgruppe der Rissoidae führt. Letztere und die potentielle Latrogastropode Maturifusus traten erstmals im Jura in Erscheinung. Erste signifikante Radiationen der Latrogastropoda nov. gingen mit der postneokomen weltweiten Erwärmung und der entsprechenden Tropisierung der Tethys einher Mit Beginn der Oberkreide differenzierten sich die Latrogastropoda infolge einer Reihe von Schlüsselinnovationen in ihre Hauptlinien. Die Wende vom Meso- zum Känozoikum spiegelt sich in der systematischen Entwurzelung der im Rezenten persistierenden Taxa wider; d.h. viele (noch genauer zu definierende) Stammlinien sind in der Erdneuzeit nicht mehr vertreten. Die weitere Evolution der Latrogastropoda nov ist durch extreme Radiationen im Eozän und im Miozän geprägt. Die neogenen supragenerischen systematischen Einheiten zeigen bereits eine hohe Übereinstimmung mit rezenten Pendants. Der relativ starke Wandel paläobiogeographischer Bezüge im Neogen korreliert also nicht mit evolutiven Innovationen von übergeordneter Bedeutung.

Description: The "higher" caenogastropods are represented by many thousand Recent and fossil species. Their characteristical shells can usually be well recognized and are frequently found particularly in marine Cenozoic deposits, thus offering excellent possibilities in respect of correlating neontological and palaeontological studies. Aim of such studies is here to trace evolution in order to obtain a basis for interpretation and actual insights respectively A more or less "holistic" approach was chosen, which translates the synthesis of conchological, anatomical, molecular genetical, reproductive biological, ecological and biogeographical data into the past and thus regarding evolution in the context of geodynamics. This approach is labelled palaeobiological conception. The different avenues of research led to the following results: the "higher" caenogastropods are very probably monophyletic and are classified as superorder Latrogastropoda nov The order Neomesogastropoda is paraphyletic because it includes the stem lineage of the Neogastropoda. It becomes apparent that many of the evolutionary lineages, which can be well defined by neontological means, are not yet correspondingly recognized in the fossil record and therefore are rooted in a systematic vacuum. The phylogenetic gaps can be defined or considered respectively by analyzing the direction of the evolution of morphological characters, which e.g. allows the creation of hypothetical fossils, which can be searched for Based upon the phylogenetic analyses, the necessity of a far-reaching revision of the classification became evident and consequently was conducted. The origin of the Latrogastropoda nov could be found in a lineage, which also leads to the stem-lineage of the Rissoidae. The latter and the potential latrogastropod Maturifusus both appeared in the Jurassic for the first time. First significant radiations of the Latrogastropoda nov correlated with the postneokomian global wanning and corresponding tropical climate of the Tethys ocean. During the early Upper Cretaceous the Latrogastropoda nov experienced key innovations which promoted the differentiation into their main lineages. The turn to the Cenozoic was accompanied by the systematic uprootal of taxa which persist in the modem fauna, which means that many stem-lineages (to be defined in detail) have not been detected in the Cenozoic. The Cenozoic evolution of latrogastropods is characterized by extreme Eocene and Miocene radiations. Neogene suprageneric systematic units show already great morphological correspondence with their Recent counterparts. Therefore the relatively strong change of palaeobiogeographic relations in the Neogene is not mirrored by principal evolutionary innovations.

Description: thesis

Description: DFG, SUB Göttingen

Description: Es wurden ca. 1500 jurassische Ammoniten mit regenerierten Verletzungen untersucht. Die Ammoniten stammen aus drei stratigraphischen Abschnitten: dem Unter-Toarcium (Süddeutschland, Südfrankreich, England) dem Ober-Callovium (Normandie / Frankreich) und dem Ober-Oxfordium (Madagaskar). Die ausgewählten Gattungen repräsentieren ein breites morphologisches Spektrum. Die Phänomene, die in Folge von Verletzungen an den Ammonitengehäusen sichtbar werden, wurden seit langer Zeit erkannt, benannt und klassifiziert. Das erfolgreichste Modell einer Klassifikation pathologischer Phänomene an Ammonitengehäusen geht auf HÖLDER (1956) zurück. Problematisch am Hölderschen Klassifikationsmodell ist das Fehlen klarer Rahmenbedingungen für das Aufstellen einer neuen forma aegra. Aus diesem Grund kam es in der Vergangenheit zu vielen, sich überschneidenden, verwirrenden und unnützen forma-Bezeichnungen. Im Rahmen der vorliegenden Arbeit wird ein stringentes Klassifikationsprinzip vorgeschlagen und eine nachvollziehbare Einordnung in dieses Prinzip gefordert. Unter dieser Prämisse werden ausgewählte forma-Bezeichnungen diskutiert. Es wird vorgeschlagen, auf die forma-Bezeichnungen: forma seccata (HÖLDER 1956), forma refecta (REIN 1994a), forma undaticarinata-undaticoncha (HENGSBACH 1996) und forma mordata (HENGSBACH 1996) zu verzichten. Als neue forma-Bezeichnungen werden eingeführt: forma augata n.f., forma umbilicata n.f. Als potentielle Verursacher regenerierbarer Schalenverletzungen konnten erkannt werden: durophage Fische (vor Allem: Lepidotes, Dapedium, Mesturas), dekapode Krebse (vor Allem: Eryma, Mecochirus) und Coleoideen. Für Verletzungen des Mantelrandepithelium (forma verticata) werden im Wesentlichen eryonide Krebse (z.B. Coleia, Proeryon, Eryon) verantwortlich gemacht. Diese Räuber lassen sich nur in Einzelfällen anhand ihrer Verletzungsspuren identifizieren. Die Ausbildung und Form der Verletzung wird im Wesentlichen von der Gehäusemorphologie bestimmt. Es lassen sich drei morphologische Variablen erkennen, die sensitiv für den Schutz vor Räubern waren: die Gehäuseform, die Wohnkammerlänge und die Skulpturierung der Schale. Dactylioceraten und Perisphinctiden, also Ammoniten mit geringer Windungsexpansionsrate, rundem Mündungsquerschnitt, langer Wohnkammer und kräftiger Skulptur waren am besten gegen räuberische Attacken geschützt. Harpoceraten und Hecticoceraten, also brevi-, mesodome, schlanke Ammoniten mit weniger kräftiger Skulptur waren schlecht gegen räuberische Attacken geschützt. Longidome Ammoniten (Dactylioceraten, Perisphinctiden) waren im Gegensatz zu den brevi-, mesodomen Ammoniten in der Lage, sich weit in die Wohnkammer zurückzuziehen. Sie konnten verletzte Schalenbereiche ausbessern, ohne dabei die Skulpturelemente wesentlich verzerren zu müssen. Longidome Ammoniten konnten aufgrund ihrer Gehäusemorphologie keine guten Schwimmer gewesen sein. Diese Ammoniten tolerierten laterale Abweichungen in der Windungssymmetrie als Verletzungsfolge und Abweichungen im Windungsquerschnitt, also Verletzungsfolgen die die Fortbewegung einschränken mußten, sehr viel besser als Morphotypen mit besseren hydrodynamischen Eigenschaften. Ammoniten konnten Schalenverlust sehr viel besser tolerieren als der rezente Nautilus. Am untersuchten Material fanden sich Ammoniten die einen Schalenverlust von 10-20 % regenerieren konnten. Beim rezenten Nautilus ist ein Schalenverlust von mehr als 4 % letal (WARD 1986). Unter der Annahme, die Ammoniten lebten, ähnlich wie Nautilus, im annähernden Schwebegleichgewicht, verweist dies auf einen sehr viel effizienteren Gleichgewichtsapparat bei den Ammoniten. Anhand des vorliegenden Materials können die als funktionell eingeschätzte Merkmale als Aptationen wahrscheinlich gemacht werden. Die relative Häufigkeit von Mehrfachverletzungen erweist sich dabei als guter Proxy für die Verletzbarkeit der Ammoniten. Die relative Häufigkeit regenerierter Verletzungen korreliert nicht mit der Verletzbarkeit der Ammoniten. Sie scheint in erster Linie die Wahrscheinlichkeit widerzuspiegeln, mit der räuberische Attacken auf den Mundrand stattgefunden haben. Gesteuert wird dieser Faktor ganz offensichtlich von der Lebensweise der Ammoniten, der sich wiederum in der Gehäusemorphologie widerspiegelt.

Description: The investigation is based on 1500 ammonoids with sublethal injuries. The observed ammonoids are Lower Toarcian (from Southern Germany / Southern France / England), Upper Callovian (from Normandy / France) and Upper Oxfordian (Madagascar). The selected ammonoid fauna represents a wide spectre of morphotypes. The healing pattern following the injuries of ammonoids have been subject to observation for a long time. The most successful model of a classification of these phenomena dates back to HÖLDER (1956). But the model of Hölder lacks a clearly defined framework for setting up a new forma aegra. For that reason many overlapping, confuse and useless forma types have been introduced. These investigation suggests a stringent principle of classification and calls for a comprehensive classification according to these principle. Following these premise, the current inventory of forma types is discussed. It is proposed to give up the terms forma seccata (HÖLDER 1956), forma refecta (REIN 1994a), forma undaticarinata-undaticoncha (HENGSBACH 1996) and forma mordata (HENGSBACH 1996). The forma-types forma augata n.f. and forma umbilicata n.f. are newly defined. Durophagous fishes (mainly Lepidotes, Dapedium and Mesturus), crustaceans (mainly Eryma and Mecochirus) and coleoids are found to be responsible for the sublethal shell breakages. Eryonid crustaceans (Coleia, Proeryon, Eryori) are most probably responsible of the healed damages of the mantle epithelia of the peristome (forma verticata, Hölder 1956). In almost all cases it is impossible to detect distinct predators by individual injuries. The character and shape of the shell breakage is defined mainly by the morphology of the shell. Three traits of the ammonoid shell are sensitive against predatory attacks: The morphology of the shell, the extension of the living chamber and the sculpture. Dactylioceratids and Perisphinctids which are longidome roughly ornamented morphotypes with a strong sculpture, a low whorl expansion and a subcircular area of aperture, are best armed against durophagous agressors. Instead Harpoceratids and Hecticoceratids, which are mesodome morphotypes with a smooth sculpture and high whorl expansion, are less armed by their shell. The longidome Dactylioceratids and Perisphinctids where in contrast to the meso- and brevidome morphotypes able to withdraw deeply in their shell. These relatively plump morphotypes tolerated an eccentric growth of the whorl (in rare cases a consequence of injury) much better than the discus-shaped Harpoceratids. Ammonoids in general tolerated a shell lost caused by a predatory attack much better than the recent Nautilus. The observed ammonoids where able to regenerate a maximal shell loss of 10-20 %. In the recent Nautilus a shell loss of more than 4 % is lethal. Under the assumption of a nearly neutral buoyant habit in life that gives evidence of a much higher efficiency of the buoyancy apparatus of the ammonoids. The traits supposed to be functional are shown to be real aptations by the frequency of multiple injuries. Multiple injuries are a good proxy of the vulnerability of the observed ammonoids. Instead the frequency of all healed injuries don’t correlate with the vulnerability but seems to be controlled mainly by the probability of a contact with a predator These factor is otherwise controlled by the habit of the ammonoids.

Description: thesis

Description: DFG, SUB Göttingen

Description: Diese Arbeit beruht auf der Nachbebenserie des Antofagasta-Bebens vom 30.07.1995. Die Nachbebenserie wurde während des CINCA ’95 Projektes in einer Zusammenarbeit zwischen den Instituten der Freien Universität Berlin und des GFZ Potsdam, im Rahmen des Sonderforschungsbereich 267, der BGR (Hannover), und des GEOMAR (Kiel) gemessen. Dazu wurde ein Netzwerk aus 50 Stationen on- und offshore im Zeitraum zwischen dem 10.08.1995 und dem 11.10.1995 betrieben. Das Netzwerk überdeckte insgesamt 310 km (22°10'S - 25°S) in Nord-Süd und 185 km (71°10'W - 69°20'W) in Ost- West-Richtung. Aus den gepickten P-und S-Einsätzen der Beben wurde mit dem Programm simulpsl2 ein 3D Geschwindigkeitsmodell berechnet. Das Modell zeigt Strukturen, die bereits früher mit aktiver Seismik gemessen wurden. So konnte entlang der Küste eine Hochgeschwindigkeitszone (vP ≈ 7.0 km/s) in 20 km, und eine Niedriggeschwindigkeitszone (vP ≈ 6.25 km/s) in 30 km Tiefe gemessen werden. Die Hochgeschwindigkeitszone wird als jurassische Unterkruste, die postjurassisch gehoben wurde, interpretiert. Im unteren Bereich kann die Hochgeschwindigkeitszone auch aus teilserpentinisierten jurassischen Mantelgestein bestehen. Als Interpretation für die Niedriggeschwindigkeitszone wird hydraulic fracturing favorisiert. Die Niedriggeschwindigkeitszone ist nicht durchgehend vorhanden. Bei 24°S befindet sich stattdessen ein Block hoher Geschwindigkeiten, der im oberen Bereich mit der Hochgeschwindigkeitszone verbunden ist. Der ozeanische Mantel konnte zwar in den Inversionen modelliert werden, jedoch war hier die Durchstrahlung nicht hinreichend, um genauere Angaben über seine Geschwindigkeit, oder seine Oberkante zu erhalten. Auch die oberen Bereiche der kontinentalen Kruste konnten nur unzureichend aufgelöst werden, da sich die Strahlen hier kaum kreuzten. Zusammen mit dem vP-Geschwindigkeitsmodell wurde auch das vP/vS- Verhältnis berechnet. Dabei konnte die Hochgeschwindigkeitszone mit einem vP/vS- Verhältnis von 1.76 - 1.81 korreliert werden. Die Niedriggeschwindigkeitszone kann mit einem vP/vS- Verhältnis von 1.67 - 1.76 korreliert werden. Mit dem 3D-Modell konnten fast alle Beben mit einer besseren Tiefengenauigkeit als 1 km lokalisiert werden. Der Hauptteil der Beben befindet sich in einem schmalen Bereich zwischen kontinentaler und ozeanischer Platte. Jedoch wurden auch einige krustale Beben detektiert. Desweiteren konnten einige Beben im ozeanischen Mantel gemessen werden. Die Bereiche, in denen das Modell gut bzw. schlecht bestimmt ist, wurden durch einen Vergleich verschiedener Modelle klassifiziert. Bei dieser Methode wurden Modelle mit verschiedenen Knotenebenen berechnet. Bereiche, in denen sich diese Modelle stark unterschieden, wurden über die Geometrische Spreizung als „schlecht aufgelöst“ klassifiziert. Weiterhin wurde die Wirkung verrauschter Daten auf die Inversion betrachtet, um den Einfluß ungenauer Picks auf das Modell zu erhalten. Zusätzlich wurden die Magnituden-Häufigkeits-Parameter für die Bebengebiete in ≈ 40 km, ≈ 100 km, sowie ≈ 200 km aus Daten verschiedener Kataloge berechnet. Es zeigte sich, daß die Beben in 100 km Tiefe nicht durch einen einzigen Magnituden-Häufigkeits-Gradienten („b-Wert“) beschreibbar sind. Dazu wurde vorgeschlagen, daß sich die tektonische Spannung hier aufbaut, und bei einer Magnitude von etwa 5.6 entlädt. Für die Beben in etwa 40 km Tiefe wurde weiterhin die zeitliche Änderung der Magnituden-Häufigkeits-Parameter zwischen 1973 und 1998 untersucht. Dabei konnte zum einen ein Trend von kleinen zu großen b- Werten zwischen 1977 und 1983 festgestellt werden. Für die nachfolgenden Jahre, bis 1995, wichen die Magnituden-Häufigkeits-Kurven fast immer so stark von einer Geraden ab, daß die Parameter nicht berechnet werden konnten. Als problematisch erwies sich die Umrechnung der Parameter zwischen den Lokalmagnituden (CINCA ’95) und den Raumwellenmagnituden (PDE-Katalog). Hier reichten die Beben, die in beiden Katalogen verzeichnet sind nicht aus, um eine Regressionsgerade zu erstellen. In Anbetracht dieser Problematik wurde in der Arbeit auch eine Methode formuliert, die Magnituden mittels der Magnituden-Häufigkeits-Parameter ineinander umzurechnen.

Description: This work is based on aftershock series of the Antofagasta event (30.07.1995). The aftershocks were recorded within the project CINCA ’95, as a collaboration between the Freie Universität Berlin and the GFZ Potsdam (within the frame of the collaborative research center 267), the BGR (Hannover) and the Geomar (Kiel). The seismological part of CINCA ’95 was performed with a network of 50 stations (on- and offshore) 10.08.95 and 11.10.95. The itself network covered an area of 310 km (22°10'S – 25°S) by 185 km (71°10'W – 69°20'W). A 3D velocity model has been obtained with the use of the program simulpsl2 from the P- and S-onsets of the events. Several structures which were known from previous active seismic experiments were resolved by the 3D model: a high velocity zone (vP ≈ 7.0 km/s) at a depth of 20 km and a low velocity zone ( vP ≈ 6.25 km/s) at a depth of 30 km. Generally, the high velocity zone is corellated to a vP/vS-ratio of 1.76 - 1.81, whereas he low velocity zone is corellated to a vP/vS-ratio of 1.67 - 1.76. The high velocity zone was explained as jurassic lower crust which was elevated in post Jurassic times. In its lower parts the high velocity zone possibly consists of former mantle material which was partly serpentinized. The low velocity zone was interpreted as material which is modified by upwelling fluids (hydraulic fracturing). In the southern part of the model (24°S) the low velocity zone is absent. In this region a block of high velocities was found which is connected to the high velocity zone. The oceanic mantle was computed within the 2D inversion step. However, the ray density was not adequate to gain sufficient information from the 3D inversion about the seismic velocity or the upper edge of the oceanic mantle. The upper regions of the continental crust were not sufficiently resolved as well. The majority of earthquakes was localized with a precision higher than 1 km. Most earthquakes were found in a small region between the continental and the oceanic plate. However, several crustal events were detected in the continental plate. Moreover, several events were detected within the oceanic mantle. A comparison of models obtained from different inversions was used to classify the quality of the regions of the model. This method included the computation of models with varying grids. Regions where the seismic velocities varied strongly with respect to the different models were classified as “low resolved“. From this classification a threshold value of the geometrical spread was determined. The influence of inexact picks on the model was investigated by inversions with noisy data. Additionally, the magnitude - frequency parameters were computed for earthquakes at ≈ 40 km, ~ 100 km and ≈ 200 km depth. As a single straight line is not adequate to describe the magnitude - frequency distribution in ≈ 100 km depth, it was proposed that the tectonic stress in this region rarely exceeds values which generate earthquakes with a magnitude of roughly 5.6. For the region of ≈ 40 km depth the temporal (1973 to 1998) variation of the magnitude - frequency parameters was investigated. It was found that the b-values increase between 1977 and 1983. In subsequent times the magnitude - frequency distribution can not be described by a straight line. The large quantity of events which were recorded within CINCA ’95 lead to accurate magnitude - frequency parameters. However, only a few events were listed in both, the PDE and the CINCA catalogue. Thus, the local - magnitudes (CINCA) could not be transformed sufficiently to body wave magnitudes by the use of regression. A formula was derived which transforms the magnitudes if all events belong to the same set of magnitude frequency parameters.

Description: thesis

Description: DFG, SUB Göttingen