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- Iran (3)
- Momententensor (2)
- Seismotektonik (2)
- moment tensor (2)
- seismotectonics (2)
- Alborz (1)
- Argentine margine (1)
- Baladeh (1)
- Central andes (1)
- Crustal density (1)
Abstract. The Sea of Marmara, in northwestern Turkey, is a transition zone where the dextral North Anatolian Fault zone (NAFZ) propagates westward from the Anatolian Plate to the Aegean Sea Plate. The area is of interest in the context of seismic hazard of Istanbul, a metropolitan area with about 15 million inhabitants. Geophysical observations indicate that the crust is heterogeneous beneath the Marmara basin, but a detailed characterization of the crustal heterogeneities is still missing. To assess if and how crustal heterogeneities are related to the NAFZ segmentation below the Sea of Marmara, we develop new crustal-scale 3-D density models which integrate geological and seismological data and that are additionally constrained by 3-D gravity modeling. For the latter, we use two different gravity datasets including global satellite data and local marine gravity observation. Considering the two different datasets and the general non-uniqueness in potential field modeling, we suggest three possible “end-member” solutions that are all consistent with the observed gravity field and illustrate the spectrum of possible solutions. These models indicate that the observed gravitational anomalies originate from significant density heterogeneities within the crust. Two layers of sediments, one syn-kinematic and one pre-kinematic with respect to the Sea of Marmara formation are underlain by a heterogeneous crystalline crust. A felsic upper crystalline crust (average density of 2720 kgm⁻³) and an intermediate to mafic lower crystalline crust (average density of 2890 kgm⁻³) appear to be cross-cut by two large, dome-shaped mafic highdensity bodies (density of 2890 to 3150 kgm⁻³) of considerable thickness above a rather uniform lithospheric mantle (3300 kgm⁻³). The spatial correlation between two major bends of the main Marmara fault and the location of the highdensity bodies suggests that the distribution of lithological heterogeneities within the crust controls the rheological behavior along the NAFZ and, consequently, maybe influences fault segmentation and thus the seismic hazard assessment in the region.
Fluvial systems are one of the major features shaping a landscape. They adjust to the prevailing tectonic and climatic setting and therefore are very sensitive markers of changes in these systems. If their response to tectonic and climatic forcing is quantified and if the climatic signal is excluded, it is possible to derive a local deformation history. Here, we investigate fluvial terraces and erosional surfaces in the southern Chilean forearc to assess a long-term geomorphic and hence tectonic evolution. Remote sensing and field studies of the Nahuelbuta Range show that the long-term deformation of the Chilean forearc is manifested by breaks in topography, sequences of differentially uplifted marine, alluvial and strath terraces as well as tectonically modified river courses and drainage basins. We used SRTM-90-data as basic elevation information for extracting and delineating drainage networks. We calculated hypsometric curves as an indicator for basin uplift, stream-length gradient indices to identify stream segments with anomalous slopes, and longitudinal river profiles as well as DS-plots to identify knickpoints and other anomalies. In addition, we investigated topography with elevation-slope graphs, profiles, and DEMs to reveal erosional surfaces. During the first field trip we already measured palaeoflow directions, performed pebble counting and sampled the fluvial terraces in order to apply cosmogenic nuclide dating (<sup>10Be, <sup>26Al) as well as provenance analyses. Our preliminary analysis of the Coastal Cordillera indicates a clear segmentation between the northern and southern parts of the Nahuelbuta Range. The Lanalhue Fault, a NW-SE striking fault zone oblique to the plate boundary, defines the segment boundary. Furthermore, we find a complex drainage re-organisation including a drainage reversal and wind gap on the divide between the Tirúa and Pellahuén basins east of the town Tirúa. The coastal basins lost most of their Andean sediment supply areas that existed in Tertiary and in part during early Pleistocene time. Between the Bío-Bío and Imperial rivers no Andean river is recently capable to traverse the Coastal Cordillera, suggesting ongoing Quaternary uplift of the entire range. From the spatial distribution of geomorphic surfaces in this region two uplift signals may be derived: (1) a long-term differential uplift process, active since the Miocene and possibly caused by underplating of subducted trench sediments, (2) a younger, local uplift affecting only the northern part of the Nahuelbuta Range that may be caused by the interaction of the forearc with the subduction of the Mocha Fracture Zone at the latitude of the Arauco peninsula. Our approach thus provides results in our attempt to decipher the characteristics of forearc development of active convergent margins using long-term geomorphic indicators. Furthermore, it is expected that our ongoing assessment will constrain repeatedly active zones of deformation. <hr> Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
The complex system of strike-slip and thrust faults in the Alborz Mountains, Northern Iran, are not well understood yet. Mainly structural and geomorphic data are available so far. As a more extensive base for seismotectonic studies and seismic hazard analysis we plan to do a comprehensive seismic moment tensor study also from smaller magnitudes (M < 4.5) by developing a new algorithm. Here, we present first preliminary results.
Erweiterte Momententensorinversion und ihre seismotektonische Anwendung : Elbursgebirge, Nordiran
(2009)
Der Elburs im Norden Irans ist ein durch die Konvergenz der Arabischen und Eurasischen Platte verursachtes doppelt konvergentes Gebirge. Das komplexe System von Blattverschiebungen und Überschiebungen sowie die Aufnahme der Deformation im Elburs ist noch nicht sehr gut verstanden. Eine neu zu entwicklende Methode zur Inversion von seismischen Momententensoren, die unterschiedliche Beobachtungen verschiedener Stationstypen kombiniert invertiert, soll die bisher hauptsächlich strukturelle/geomorphologische Datengrundlage um Momententensoren auch kleinerer Magnituden (M < 4.5) erweitern. Dies ist die notwendige Grundlage für detaillierte seismotektonische Studien, die wiederum die Basis für seismische Gefährdungsanalysen bilden.
Integration of digital elevation models and satellite images to investigate geological processes.
(2006)
In order to better understand the geological boundary conditions for ongoing or past surface processes geologists face two important questions: 1) How can we gain additional knowledge about geological processes by analyzing digital elevation models (DEM) and satellite images and 2) Do these efforts present a viable approach for more efficient research. Here, we will present case studies at a variety of scales and levels of resolution to illustrate how we can substantially complement and enhance classical geological approaches with remote sensing techniques. Commonly, satellite and DEM based studies are being used in a first step of assessing areas of geologic interest. While in the past the analysis of satellite imagery (e.g. Landsat TM) and aerial photographs was carried out to characterize the regional geologic characteristics, particularly structure and lithology, geologists have increasingly ventured into a process-oriented approach. This entails assessing structures and geomorphic features with a concept that includes active tectonics or tectonic activity on time scales relevant to humans. In addition, these efforts involve analyzing and quantifying the processes acting at the surface by integrating different remote sensing and topographic data (e.g. SRTM-DEM, SSM/I, GPS, Landsat 7 ETM, Aster, Ikonos…). A combined structural and geomorphic study in the hyperarid Atacama desert demonstrates the use of satellite and digital elevation data for assessing geological structures formed by long-term (millions of years) feedback mechanisms between erosion and crustal bending (Zeilinger et al., 2005). The medium-term change of landscapes during hundred thousands to millions years in a more humid setting is shown in an example from southern Chile. Based on an analysis of rivers/watersheds combined with landscapes parameterization by using digital elevation models, the geomorphic evolution and change in drainage pattern in the coastal Cordillera can be quantified and put into the context of seismotectonic segmentation of a tectonically active region. This has far-reaching implications for earthquake rupture scenarios and hazard mitigation (K. Rehak, see poster on IMAF Workshop). Two examples illustrate short-term processes on decadal, centennial and millennial time scales: One study uses orogen scale precipitation gradients derived from remotely sensed passive microwave data (Bookhagen et al., 2005a). They demonstrate how debris flows were triggered as a response of slopes to abnormally strong rainfall in the interior parts of the Himalaya during intensified monsoons. The area of the orogen that receives high amounts of precipitation during intensified monsoons also constitutes numerous landslide deposits of up to 1km<sup>3 volume that were generated during intensified monsoon phase at about 27 and 9 ka (Bookhagen et al., 2005b). Another project in the Swiss Alps compared sets of aerial photographs recorded in different years. By calculating high resolution surfaces the mass transport in a landslide could be reconstructed (M. Schwab, Universität Bern). All these examples, although representing only a short and limited selection of projects using remote sense data in geology, have as a common approach the goal to quantify geological processes. With increasing data resolution and new sensors future projects will even enable us to recognize more patterns and / or structures indicative of geological processes in tectonically active areas. This is crucial for the analysis of natural hazards like earthquakes, tsunamis and landslides, as well as those hazards that are related to climatic variability. The integration of remotely sensed data at different spatial and temporal scales with field observations becomes increasingly important. Many of presently highly populated places and increasingly utilized regions are subject to significant environmental pressure and often constitute areas of concentrated economic value. Combined remote sensing and ground-truthing in these regions is particularly important as geologic, seismicity and hydrologic data may be limited here due to the recency of infrastructural development. Monitoring ongoing processes and evaluating the remotely sensed data in terms of recurrence of events will greatly enhance our ability to assess and mitigate natural hazards. <hr> Dokument 1: Foliensatz | Dokument 2: Abstract <hr> Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
The southern Central Andes (SCA) (between 27 degrees S and 40 degrees S) is bordered to the west by the convergent margin between the continental South American Plate and the oceanic Nazca Plate. The subduction angle along this margin is variable, as is the deformation of the upper plate. Between 33 degrees S and 35 degrees S, the subduction angle of the Nazca plate increases from sub-horizontal (< 5 degrees) in the north to relatively steep (similar to 30 degrees) in the south. The SCA contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated Cenozoic deformation within the Andean orogen. The distribution of the deformation within the SCA has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities. However, the possible influence that the thickness and composition of the continental crust have had on both short-term and long-term deformation of the SCA is yet to be thoroughly investigated. For our investigations, we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the Andean orogeny and, in particular, investigated the short- and long-term nature of the present-day deformation processes. We established a 3D model of lithosphere beneath the orogen and its foreland (29 degrees S-39 degrees S) that is consistent with currently available geological and geophysical data, including the gravity data. The modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains: the crystalline crust in the orogen (the magmatic arc and the main orogenic wedge) is thicker (similar to 55 km) and less dense (similar to 2900 kg/m(3)) than in the forearc (similar to 35 km, similar to 2975 kg/m(3)) and foreland (similar to 30 km, similar to 3000 kg/m(3)). Crustal thickening in the orogen probably occurred as a result of stacking of low-density domains, while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion. No clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early Paleozoic. Areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal-density contrast. This suggests that the short-term deformation within the interior of the Andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers. A thicker, denser, and potentially stronger lithosphere beneath the northern part of the SCA foreland is interpreted to have favoured a strong coupling between the Nazca and South American plates, facilitating the development of a sub-horizontal slab.
Uplift in the broken Andean foreland of the Argentine Santa Bárbara System (SBS) is associated with the contractional reactivation of basement anisotropies, similar to those reported from the thick-skinned Cretaceous-Eocene Laramide province of North America. Fault scarps, deformed Quaternary deposits and landforms, disrupted drainage patterns, and medium-sized earthquakes within the SBS suggest that movement along these structures may be a recurring phenomenon, with yet to be defined repeat intervals and rupture lengths. In contrast to the Subandes thrust belt farther north, where eastward-migrating deformation has generated a well-defined thrust front, the SBS records spatiotemporally disparate deformation along structures that are only known to the first order. We present herein the results of geomorphic desktop analyses, structural field observations, and 2D electrical resistivity tomography and seismic-refraction tomography surveys and an interpretation of seismic reflection profiles across suspected fault scarps in the sedimentary basins adjacent to the Candelaria Range (CR) basement uplift, in the south-central part of the SBS. Our analysis in the CR piedmont areas reveals consistency between the results of near-surface electrical resistivity and seismic-refraction tomography surveys, the locations of prominent fault scarps, and structural geometries at greater depth imaged by seismic reflection data. We suggest that this deformation is driven by deep-seated blind thrusting beneath the CR and associated regional warping, while shortening involving Mesozoic and Cenozoic sedimentary strata in the adjacent basins was accommodated by layer-parallel folding and flexural-slip faults that cut through Quaternary landforms and deposits at the surface.
Portal Wissen = Layers
(2013)
The latest edition of our Potsdam Research Magazine “Portal Wissen” addresses the topic “Layers” in many different ways. Geoscientists often deal with layers: layers of soil, sediment, or rock are the evidence of repeated and long-lasting processes of erosion and sedimentation that took place in the early history of the earth. For instance, mountains are eroded by water, ice and wind. The sand that results from that erosion might eventually form a new layer on the ocean floor known as a sediment horizon. After tens of millions of years, tectonic plate movements can deform the ocean floor, pushing it upwards as mountains are created, bringing the layers of sand from former mountain chains together with fossilized sea dwellers into the realm of climbers and mountaineers – a fundamental cycle within the Earth system that was succinctly described by Ibn Sina nearly 1000 years ago, and later by Charles Darwin when he was crossing the Andes.
The landscape around us overlays the products of recent processes with those from the past. Slow processes or extreme events that happen very rarely – like floods, earthquakes or rockslides – wipe out certain characteristics, while others remain on the surface. In this sense, the landscape is like a palimpsest – a piece of parchment that monks in the Middle Ages scraped clean again and again to write something new. Analysing rock layers and soil is similar to the work of a detective. Geophysical deep sounding with sound and radar waves, precise measurements of motions related to earthquakes, and deep boreholes each provide a glimpse of the characteristics of what lies beneath us, giving us a better understanding of spatial distribution of the various layers. Fossils can tell us the age of a layer of sediment, while radiometric isotopes in minerals reveal how quickly a rock moved from deep within the Earth up to the surface, perhaps during the process of mountain building. Thin layers of ash tell us when there was a devastating volcanic eruption that influenced environmental conditions. The shape, gradation, and surface conditions of sand grains reflect whether wind or water was responsible for their transport. We know, for instance, that northern Germany was a desert landscape more than 260 million years ago. At that time, the wind made huge dunes migrate across the region. Over time, climate and vegetation slowly alter the physical and chemical characteristics of sand and rock at the surface, turning them into soil, the epidermis of our planet. Mineralogical analyses of layers of the soil layer tell us whether the climate was dry or wet. These kinds of observations allow us to reconstruct links between our climate system and processes that have taken place on the Earth’s surface, as well as those processes that originate at much deeper levels. The clues we use might be hidden under the surface of the earth or clearly visible on the surface, like in the mountains, or even in freshly cut rock alongside roads.
On the following pages, we invite you to accompany scientists from Potsdam into their world of research. They track hidden traces of longgone earthquakes in the Tien Shan Mountains; they discover ancient forms of life in deep-sea sediments. They even examine layers in outer space that can tell us something about the formation of planets. “Portal Wissen” not only presents scientists of the University of Potsdam who deal with the sequence of layers formed by solid rock, but also those scientists who deal with levels of education or social strata. Research scientists explain how to implement the social mission of inclusion in teaching, and how pupils from the Berlin district Kreuzberg examine language in urban neighbourhoods together with students from the University of Potsdam.
Although these types of “layers” are very different, they all have something in common. Their structure and profile are evidence of continuously changing conditions. The present will leave traces and layers that future geoscientists will measure and examine. We already speak of the Anthropocene, a geological era dominated by humans, which is characterized by far-reaching changes in erosion and sedimentation rates, and the displacement of natural habitats. I hope that you will discover exciting and inspiring stories in this edition. And remember – it is always worth having a look beneath the surface.
Prof. Manfred Strecker, PHD
Professor of Geology
Portal Wissen = Schichten
(2013)
Die neue Ausgabe unseres Potsdamer Forschungsmagazins widmet sich ganz und gar und auf sehr unterschiedliche Weise dem Thema „Schichten“.
Als Geowissenschaftler begegnen mir Schichten häufig: Boden-, Sedimentoder Gesteinsschichten – sie sind das Zeugnis lang anhaltender und immer wiederkehrender Erosionsund Ablagerungsprozesse, wie sie schon in der frühen Erdgeschichte stattfanden. Gebirge werden beispielsweise durch Wasser, Eis und Wind erodiert. Die Erosionsprodukte bilden vielleicht irgendwann auf dem Meeresgrund als Ablagerungshorizont eine neue Schicht. Umgekehrt führen Deformationsprozesse als Folge von tektonischen Plattenbewegungen dazu, dass Gebirge entstehen und der Mensch versteinerte Meeresbewohner in verfalteten Sedimentschichten im Hochgebirge findet – Beziehungen, wie sie bereits von Ibn Sina und später von Charles Darwin bei seiner Andenüberquerung beschrieben wurden. Aber auch die Landschaft, die wir bei einem Blick aus dem Fenster wahrnehmen, ist nichts anderes als das Produkt verschiedener Überlagerungen von Prozessen Liebe Leserinnen und Leser, in der Vergangenheit und heute. Langsam ablaufende Prozesse oder seltener stattfindende Extremereignisse wie Fluten, Erdbeben oder Bergstürze – einzelne Merkmale werden dabei ausgelöscht, andere treten zutage. Ähnlich einem Palimpsest – einem Stück Pergament, das die Mönche im Mittelalter immer wieder abgeschabt und neu überschrieben haben. Die Analyse von Gesteins- und Bodenschichten gleicht der Arbeit eines Detektivs. Geophysikalische Tiefensondierungen mit Schall- und Radarwellen, die genaue Vermessung von Erdbebenherden oder Tiefbohrungen bringen uns verdeckte Erdschichten näher. Fossilienfunde und radiometrische Datierungen verraten das Alter einer Schicht. Mithilfe dünner Ascheschichten können wir nachweisen, wann verheerende Vulkanausbrüche Umweltbedingungen beeinflusst haben.
Böden, die Epidermis unseres Planeten, spiegeln die Eigenschaften der darunterliegenden Gesteinsschichten, der Vegetationsbedeckung oder den Einfluss des Klimas wider. Die Form, Sortierung und Oberflächenbeschaffenheit von Sandkörnern lassen uns erkennen, ob Wind oder Wasser für ihren Transport gesorgt haben. So wissen wir, dass Norddeutschland vor über 260 Millionen Jahren eine Wüstenlandschaft war, in der der Wind mächtige Dünen wandern ließ. Die mineralogische Untersuchung damit verbundener Schichten verrät, ob das Klima trocken oder feucht war. So dechiffrieren wir Hinweise auf vergangene Prozesse, die unter der Erdoberfläche versteckt sind oder – wie etwa in Gebirgen – offen zutage treten.
Auf den kommenden Seiten laden wir Sie ein, Potsdamer Wissenschaftler an die Orte ihrer Forschung zu begleiten: Im Tien Shan-Gebirge spüren sie längst vergangene Erdbeben auf, in Tiefseesedimenten entdecken sie uralte Lebensformen und im Weltall erforschen sie gar Schichten, die uns etwas über die Entstehung von Planeten verraten. Die Wissenschaftler der Universität Potsdam beschränken sich allerdings nicht auf die Schichtabfolgen der festen Erde. „Portal Wissen“ blickt auch jenen Wissenschaftlern über die Schulter, die sich mit „Bildungsschichten“ oder „Gesellschaftsschichten“ befassen. So erklären Forscher, wie der gesellschaftliche Auftrag der Inklusion in der Lehre umgesetzt wird oder wie Kreuzberger Schüler zusammen mit Potsdamer Studierenden Sprache im urbanen Raum erforschen.
So unterschiedlich sie sind, eines ist allen diesen „Schichten“ gemeinsam: Ihre Struktur und Form sind Zeugnis sich immer wieder verändernder Rahmenbedingungen. Auch die Gegenwart wird Spuren und Schichten hinterlassen, die zukünftige Erdwissenschaftler vermessen und untersuchen werden. Schon jetzt spricht man vom Anthropozän, einem vom Menschen dominierten geologischen Zeitabschnitt, charakterisiert durch tiefgreifende Änderungen in den Erosions- und Sedimentationsraten und der Verdrängung natürlicher Lebensräume.
Ich wünsche Ihnen, dass Sie in diesem Heft spannende und anregende Geschichten entdecken. Denn es lohnt sich, einen Blick unter die Oberfläche zu werfen.
Prof. Manfred Strecker, PhD.
Professor für Allgemeine Geologie
The northward movement and collision of the Arabian plate with Eurasia generates compressive stresses and resulting shortening in Iran. Within the Alborz Mountains, North Iran, a complex and not well understood system of strike-slip and thrust faults accomodates a fundamental part of the NNE-SSW oriented shortening. On 28th of May 2004 the Mw 6.3 Baladeh earthquake hit the north-central Alborz Mountains. It is one of the rare and large events in this region in modern time and thus a seldom chance to study earthquake mechanisms and the local ongoing deformation processes. It also demonstrated the high vulnerability of this densily populated region.