During the cruise with S.V. EXPLORA within the Ross Sea on the second marine-geophysical expedition of the Federal Institute for Geosciences and Natural Resources (BGR) to Antarctica, in total 6,745 km of magnetic, gravity and digital reflection seismic lines and additionally 1,400 km gravity lines were acquired in the period from January 10th to March 2nd 1980. On 43 stations sonobuoy refraction measurements have been carried out. The main results are: (1) In the eastern part of the Ross Sea Shelf two striking discontinuities have been identified in the reflection seismics representing gaps in the sediments at the turn-over of the Upper Miocene to the Pliocene (ca. 7 mio years B.P.) and between the Middle and Upper Miocene (ca. 11.5 mio. years B.P.) according to results of DSDP boreholes. (2) In the southern part of the Ross Sea Shelf the basement is uncovered at depths over 700m due to a thrust of the shelf ice recently. (3) A structural unit extends alongside the meridian of 180° separating the Ross Sea into two different geologic regions. This unit is characterised by two basement highs with seismic velocities exceeding 5 km/sec. (4) In relation with the GANOVEX expedition two profiles have been measured off northern Victoria Land which indicate two large faults with a faulting amount of 2 km. Another area is characterised by intrusive and volcanic bodies.
Main target of the project GIGICS (Cooperative German-Indonesian Geoscientific Investigations in the Celebes Sea) is the investigation of the internal crustal structure and the plate tectonic evolution of the Celebes Sea and its active continental margins off Mindanao and Northern Sulawesi. These investigations were carried out during the cruise SO98 of RV SONNE by the Federal Institute for Geosciences and Natural Resources (BGR), Hannover; the German Research Centre for Geosciences (GFZ), Potsdam; the GEOMAR, Kiel; the Institute of Oceanography (IfM), Hamburg; the Mines and Geoscience Bureau, Manila; the Agency for the Assessment and Application of Technology, Jakarta, and the Institute of Oceanography, Wormley. The cruise SO98 consisted of three legs of two weeks duration and one leg of four weeks duration. The total amount of data acquired during the cruise were: - 3,300 km of multichannel reflection seismics, - over 6,800 km of gravimetric and magnetic data and approximately 10.000 km of swath bathymetric and sediment echosounder data, - 3 wideangle-/refractionseismic profiles, each of 120 - 150 km length, - geological, geochemical sampling and oceanographical measurements at a total of 37 stations. During the cruise SO98 a widespaced but regular grid of magnetic and gravimetric profiles were acquired in the eastern part of the Celebes Sea from which up to then reliable data were very sparse. WEISSEL (1980) recognized in the western Celebes Sea WSW-ENE striking magnetic lineations, which he interpreted as chrons 18 - 20 (39 - 43 Ma according to the timescale of HARLAND et al. (1990)). The data from cruise SO98 show that there is no continuation of these anomalies to the east. In the eastern part the magnetic field of the Celebes Sea is less clear and much more disturbed. Nevertheless, E-W-striking anomalies are recognizable. Because amplitudes of local magnetic anomalies are higher than the lineations, the correlation of these lineations with the magnetic reversal scale is still somewhat ambiguous. The gravity map compiled from the measured gravimetric data shows elongated positive anomalies in the eastern part of the Celebes Sea. Exceptions occur at the deep sea trenches off North Sulawesi (North Sulawesi Trench) and Mindanao (Cotabatu Trench) and at the Sulu Archipelago where strong negative gravity anomalies were found. A remarkable NW-striking gravity high of up to 60 mgal was found in the central eastern part of the Celebes Sea. Gravimetric modelling suggests that this high can be correlated with the gravimetric effect of the Molucca Sea Plate subducting from the east under the Sangihe Arc. The reflection seismic data from the northern part of the Celebes Sea show indications for a juvenile subduction of oceanic Celebes Sea crust under the Sulu Archipelago. The oceanic crust bends down towards the Sulu Arc with angles between 2° and 5° and the sedimentary sequence above is deformed indicating a compressional stress regime. With the exception of two linear arranged seamount-like basement highs the Celebes Sea is dominated by two different oceanic crustal types showing distinct differences in the topography. The first one is showing a very similar reflection seismic pattern as it is found for oceanic crust of the Atlantic (HINZ et al., 1994). This type is characterized by a small-scale block-faulted relief of the top basement and a low reflectivity in lower crustal levels typically related as to be accreted at slow to intermediate spreading ridges. This type is found in the western, northern and southern part of the investigated area. In the eastern and especially in the southeastern part the igneous crust shows a very different image. The reflection of the top of the basement is less distinct and of lower frequency. The relief is very much smoother than in the previous type. This reflection seismic image indicates a volcanic/magmatic overprinting of the oceanic crust in this part of the Celebes Sea. Another target of cruise SO98 was the area of the active continental margin off North Sulawesi and its accretionary complex. The internal structure of the accretionary complex should be investigated to decide whether this active margin is also of the 'splinter-type' or not. During former geophysical cruises with RV SONNE oceanic crustal splinters were discovered in the accretionary wedges of the Sulu Sea and off Costa Rica (e.g. HINZ et al., 1991). From our reflection seismic measurements this active continental margin is morphologically subdivided into three units and consists of two accretionary complexes of different internal structural style: the lower and middle continental slope is underlain by an intensively thrusted, sedimentary accretionary wedge. This wedge was most probably formed during the last 5 Ma. Landward of this wedge an older and seismically very complex accretionary unit is present which is overlain at its landward termination by a sedimentary fore-arc basin. Within this older accretionary complex, units with a strong, low frequency reflection pattern were found which are interpreted to represent crustal splinters of igneous oceanic or ophiolitic nature. This interpretation is supported by our gravity and magnetic data. The magnetic profiles show an increase of the magnetic field towards the north arm of Sulawesi across the continental margin. This increase of the magnetic field suggests an increase of magnetized material within the older accretionary wedge towards the northern arm of Sulawesi where ophiolites are emplaced. During the interpretation of the reflection seismic data of the project GIGICS BSR's (bottom simulating reflectors) were discovered for the first time along the active continental margin of North-Sulawesi. BSR's are the seismic expression of a velocity decrease at the bottom of a gas hydrate zone. The distribution and depth of the BSR's correlates with the geochemical and geothermal results. Radiometric age dating and geochemical analyses from pillow basalts of a seamount from the southeastern Celebes Sea indicate hot-spot activity in this part of the Celebes Sea during or shortly after the formation of the oceanic crust approximately at 43 Ma ago. Three NW-striking ridges or seamount-chains in the northeastern Celebes Sea were mapped and investigated in detail. They are thought to represent a wrench fault system extending through the northeastern Celebes Sea. At the flank of one of these ridges a strongly alterated plagioclase-olivine basalt sample was dredged which was overlain by non-fossiliferous clay stone. A similar lithostratigraphic sequence was drilled during ODP leg 124 (RANGIN et al., 1990). The geochemical composition of these basalts is different from typical MORB. The existence of a large crustal splinter within the accretionary wedge off southwestern Mindanao obviously is responsible for a high thermal conductivity which in turn could have enhanced heat flow (108.1 mW/m2) and methanogenesis (405 ppb). The heat flow of 103.0 mW/m2 at the deformation front of the Mindanao wedge and the high methane concentration of 5.555 ppb suggests tectonically induced fluid transport within the wedge. High methane concentrations between 8.044 and 49.006 ppb at the lower slope off Sulawesi and in the North Sulawesi Trench are accompanied by high heat flow values of up to 100.5 mW/m2. Heat flow is significantly lower upslope (31.3 mW/m2). This general heat flow distribution pattern is seen over a large portion of the accretionary wedge. The elevated heat flow values and high methane concentrations near the deformation front most likely result from heat transport by fluids squeezed out from vertically and laterally compacting sediments. The reduced heat flow towards the coast is compatible either with a cooling effect of slow subduction of the oceanic crust, or stacking of cool slabs of compacted sediments. A subduction of oceanic crust with a heat flow around 60 mW/m2 over a period of more than 3 million years would have produced the low heat flow values of the upper slope if the wedge consists of claystone with a low thermal conductivity (1.2 - 1.7 W/mK). Even in the low-heat flow area isolated fluid venting is possible. Lateral variations in the heat flow pattern (e.g. broadening of the anomalies in the west) may be due to different thermal regimes within the subducted crust.
From 19th November to 19th December 2004 BGR conducted a marine geophysical cruise between 34°S and 36°S off Uruguay and between 46°S and 50°S off Argentine. The main research objective was to contribute to a better understanding of the initial breakup and the early opening of the South Atlantic. In continuation of our former work on the South Atlantic continental margins off Argentina, Brazil, Uruguay, Namibia and South Africa marine geophysical research (multi-channel seismics, refraction-/wide-angle reflection seismics, magnetics and gravity) was performed in close cooperation with the Argentine and Uruguayan authorities Comisión Nacional del Límite Exterior de la Plataforma Continental (COPLA) of Argentina and Servicio de Oceanograficia, Hidrograficia y Meteorologia de la Armada (SOHMA) of Uruguay. Multi-channel seismic lines with a total length of 3,754 km and additional 3540 km with the other geophysical methods were acquired . Along two lines refraction-/wide-angle reflection seismic work was carried out. The preliminary analyses of the new seismic data show different images of the crustal structures between Uruguay and southern Argentine with regard to the distribution and volume of offshore volcanic rocks (seaward dipping reflector sequences, SDRS) along the South American Atlantic margin. On the northern profiles between 34°S and 36°S one single well developed wedge of SDRS is present. Although the landward termination (‘feather edge’) on most of the lines is masked by multiples the average total width of the wedge across the margin seems to be 90 – 100 km and is very constant for this margin segment. This is strong contrast to the results from former cruises (BGR87, SO85 and BGR98) which covered the area between 38°S and 45°S. There, the SDRS showed distinct multiple wedges which in some places extend over 120 km across the continental slope. The investigation of the sedimentary section yielded that in the area off Uruguay widespread bottom simulating reflectors (BSR) are present. This indications for stable gas hydrates cover a total area of 7000 km2. One major aim of the cruise was to cover the transition between a volcanic passive margin and a non-volcanic passive resp. sheared margin. This was accomplished in the southern part of the investigated area. Two EW-trending profiles across the Argentine shelf into the Argentine Basin still show indications for SDRS but these structures are only 25 – 30 km wide. The profiles which extend from the NE to the SW crossing the Agulhas-Falkland Fracture Zone (AFFZ) onto the Falkland Plateau show the typical trend of a sheared margin. At the northern rim of the Falkland Plateau a set of small pre-rift half grabens were found indicating pre-rift extensional tectonic phases. The magnetic data in the area off Uruguay show lineations which are preliminary interpreted as chrons M0 to M3. This might indicate that the first (oldest) oceanic crust was created at a time around the magnetic polarity reversal between the normal interval M4 and the reversed interval M3 (126-127 Ma). Together with existing data from previous cruises this indicates that the breakup of the South Atlantic started further South because there magnetic chrons back to M9 (130 Ma) were identified. In the southernmost part of the margin at 47°S only the magnetic lineations M0 to M4 were identified in the oceanic domain Nevertheless, it is likely that between M4 and the assumed position of the continent ocean boundary/transition (COB/COT) older oceanic crust exists that for some reasons does not show correlatable lineations. The the free-air gravity map is dominated by the main topographic and structural features in the survey area. Rifted continental margins are characterized by prominent free-air gravity anomalies elongated parallel to the ocean-continent transition. The continental slope is considerably steeper in the North off Uruguay than in the South and thus the gravity high is much more pronounced in the North than in the South. The simple Bouguer anomaly map also shows the difference between the more gentle and wider continental slope in the South and the steeper slope in the North. The lowest Bouguer gravity values are found in the area of the basins on the continental shelf. Especially the Salado Basin in the prolongation of the Rio de la Plata and the Colorado Basin at about 40°S are indicated by Bouguer gravity anomaly highs. The interpretation by forward density modelling shows, however, the presence of SDRS units in the North of relative high density in the area of the continental slope. Whereas the modelling shows no indications for such volcanic bodies in the South. Although the MCS data indicate a small SDRS wedge but this body may be too small to cause an anomaly.From 17th April to 6th June 2003 BGR conducted a marine geophysical cruise between 30°S and 38°S off the Atlantic coast of South Africa. The main research objective was to contribute to a better understanding of the initial breakup and the early opening of the South Atlantic. In continuation of our former work on the South Atlantic continental margins off Argentina, Brazil, Uruguay and Namibia marine geophysical research (multi-channel seismics, wide-angle refraction seismics, magnetics and gravity) was performed in cooperation with the Petroleum Agency South Africa (PASA). Multi-channel lines with a total lenght of 3,260 km, and additional 1,365km, with the other geophysical methods were acquired. Combined onshore/offshore refraction seismic work in cooperation with GeoForschungsZentrum Potsdam (Germany) and the Council for Geoscience (South Africa) was also part of the program.
The main purpose of the cruise SO75 from 14th October to 12th November 1991 was to test the new instrumentation of the SONNE and the ship itself for the needs of marine geophysics. The second purpose was the investigation of the crustal structure of the Atlantic Ocean from the Madeira-Torre Rise to the continental slope of Portugal which is conjugate to the margin off Newfoundland being investigated by a previous BGR cruise (Hinz et al., 1989). Methods used were multichannel reflection seismics, gravimetry, magnetics, swath echosounding and sediment echography. The test of the ship and its result is discussed in a separate technical report (Roeser et al., 1991). On two lines crossing the Madeira-Torre Rise we have observed seaward dipping reflector sequences. Their position is conjugate to similar features observed off Newfoundland. Magnetic models for one line show a strong magnetization of the whole reflector sequence. Thus, in analogy to the drilled dipping reflector sequence on the Vøring Plateau, it is likely that it mainly consists of lava flows which were extruded subaerially or in shallow water. In contrast to the dipping reflector sequences found earlier, the newly detected sequences are far away from continental crust. Presumably, at the time of their formation the Midatlantic Ridge was subaerial. Geometrical constraints indicate a compressional regime for the eastern part of the Azores-Gibraltar Fracture Zone. Most prominent expression of this is the Gorringe Bank. Our seismic line across it indicates an overthrusting of oceanic crust, however, it does not show any evidence for a Benioff zone. Therefore, only a small amount of oceanic crust can be subducted until now. We have observed compressional features also in the Tagus Abyssal Plain. Our lines north of the Azores-Gibraltar Fracture Zone did not confirm the weak indications for a continuation of the magnetic anomaly M0 across the fracture zone. The present platetectonic models for this area require therefore a modification. For the definition of the ocean-continent transition in the Iberia Abyssal Plain and for the investigation of the nature of the crust near the transition zone 6 ODP drillsites have been proposed. In response to a request by R.B. Whitmarsh from the Institute of Oceanographic Sciences at Wormley, Godalming, we have carried out the required ODP Site Survey.
In the scope of International Geoscientific Programs and in close cooperation with PETRONAS, Malaysia, and in agreement with the Bureau of Mineral Resources (BMR) and the Bureau of Energy Development (BED), Manila, the Federal Institute for Geosciences and Natural Resources (BGR) carried out a geophysical survey on the continental margin off Sabah during the period from 20th July to 10th August, 1986, and in the Northwestern Sulu Sea during the period from 12th August to 28th August, 1986, using the PRAKLA-SEISMOS vessel EXPLORA chartered by the BGR. The research cruise is a continuation of BGR’s marine geoscientific studies in the South China Sea and in the Sulu Sea with the German research vessels VALDIVIA (1977), SONNE (1982/83) and EXPLORA (1984). The previous investigations provided new information regarding the geological and tectonic history of the southern part of the South China Sea in the context of plate tectonics. According to the interpretation of the large amount of geophysical, geological and geochemical data collected by BGR on previous cruises the widely accepted hypotheses of the presence of an ancient subduction zone beneath the Sabah-Palawan Trough has to be revised. The main objective of the EXPLORA cruise was to search for an Oligocene-Early Miocene carbonate platform off Sabah and in the western Sulu Sea. On the continental margin off Sabah 27 lines were surveyed with gravity and multichannel reflection seismics and partly with magnetics, with a total length of 3,126 km. A strong reflector interpreted as reflector BLUE of previous BGR cruises off Palawan was recognizable beneath the Sabah Trough in depth between 4 and 7 sec (TWT). The isochrones of the reflector strike approximately 50°N. The surface of the reflector dips with 2 to 3 degree towards southeast. Toward the north-western part of the Sabah Trough the reflector is disrupted by a basement high. According to the preliminary interpretation of the gravity data, the prominent free-air anomaly associated with the Sabah Trough and adjacent areas has the same shape as the anomaly observed across the Palawan Trough. Therefore it is concluded that the Sabah Trough is underlain by a thinned continental crust.
The Sonne Cruise SO122 was carried out by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover) from 3rd August to 9th September 1997, in cooperation with GEOMAR (Kiel), the National Institute of Oceanography (NIO, Karachi) and the Hydrocarbon Development Institute of Pakistan (HDIP). During the joint project with R/V SONNE the Makran accretionary wedge off Pakistan should have been investigated in detail with multi-channel reflection seismics, magnetics and gravimetry. Intense fishery offshore Pakistan forced a change of the area of investigation to the south with the following objectives: investigation of the crustal structure and occurrence of the bottom simulating reflector (BSR) in the Makran accretionary wedge; investigation of the structure of the Murray Ridge System in order to reconstruct the geodynamic evolution of the eastern Indian Plate margin; determination of the origin of the crust underlying the Indus Fan and reconnaissance of the sedimentary history of the Indus Fan in order to reveal the uplift and erosion history of the Himalayas.
Thematische Karten mit der Darstellung geophysikalischer Merkmale des geologischen Untergrundes in verschiedenen Maßstäben: 1. Regionales Kartenwerk Reflexionsseismik - Tiefenlinienkarten relevanter geologischer Leithorizonte in den Maßstäben 1:100000 und 1:200000 2. Komplexgeophysikalische Strukturkarte der DDR im Maßstab 1:500000 3. Magnetanomalien der Totalintensität im Maßstab 1:500000 4. Laufzeiten des seismischen Impulses im Maßstab 1:500000 5. Schwerekarte der Länder Brandenburg, Mecklenburg-Vorpommern, Sachsen, Sachsen-Anhalt und Thüringen im Maßstab 1:500000 6. Geologische Karte von Mecklenburg-Vorpommern - Strukturen im Untergrund nach oberflächengeophysikalischen Ergebnissen im Maßstab 1: 500 000 Zusätzliche Informationen Datengewinnung: analog, liegt vor als: Karte, beziehbar: analog
Das Projekt "Abbilden steil stehender Strukturen mit Diffraktionen - AP 2" wird vom Umweltbundesamt gefördert und von Universität Hamburg, Zentrum für Meeres- und Klimaforschung, Institut für Geophysik durchgeführt. Ziel des Vorhabens ist die Entwicklung und Anwendung von Methoden zur Nutzung des Abbildungspotentials von Diffraktionen. Das Verfahren entsprich einer Full Waveform Imaging Methode und weist Super-Stacking und Super-Resolution Eigenschaften auf. Das Verfahren unterscheidet sich von herkömmlichen Abbildungsverfahren vor allem dadurch, dass der gesamte Wellenzug einschließlich der Coda für die Abbildung genutzt wird. In einem ersten Bearbeitungsschritt der Daten sollen Diffraktionen und Reflexionen separiert werden. Hierzu müssen CRS Attribute bestimmt werden sowie ein tomographisches Geschwindigkeitsmodell für den Untergrund entwickelt werden. Mit diesem können die Diffraktoren im Raum lokalisiert werden. Damit ist der Ort der zugehörigen Beobachtung (Greensche Funktion) gefunden. Durch Wellenfeldfortsetzung kann diese Beobachtung für Positionen in die nähere Umgebung berechnet werden. Dieses Feld von Greenschen Funktionen wird dann für die lokale hochauflösende Abbildung genutzt. Das Abbildungsverfahren entspricht dabei einer Reverse Time Migration, wobei anstatt des modellierten Wellenfelds die beobachteten und fortgesetzten Greenschen Funktionen genutzt werden. In das Abbildungsverfahren geht die komplette Wellenform einschließlich der Coda ein.
Das Projekt "FS SONNE: SO 161 - SPOC: Subduktionsprozesse vor Chile" wird vom Umweltbundesamt gefördert und von Bundesanstalt für Geowissenschaften und Rohstoffe durchgeführt. Mit dem Verbundvorhaben SPOC (Subduction Processes Off Chile) wird versucht die Prozesse, die im Zusammenhang mit der Subduktion der ozeanischen Platte am Kontinentalrand von Südamerika ablaufen, besser zu verstehen. Dazu wurden exemplarisch zwei Arbeitsgebiete ausgewählt, in denen die entsprechenden Subduktionsbedingungen, die zu Akkretion bzw. Erosion an der Kontinentalplatte oder entsprechenden Mischformen am Kontinentalrand Chiles führen. Unter Einsatz eines umfangreichen geophysikalischen Messprogramms (Reflexionsseismik, Magnetik, Gravimetrie Geothermie) und geologisch, geochemischer Untersuchungen (Teilprojekt I) sollen Modelle entwickelt werden, die letztlich Aussagen zum Nutzungs- und Gefährdungspotential an aktiven Kontinentalrändern ermöglichen. Mit Hilfe von seismischen Weitwinkelmessungen und dem Ausbringen eines seismologischen Netzes (Teilprojekt II) soll der Krustenaufbau der ozeanischen Platte und die Erdbebenverteilung untersucht werden, die ebenfalls Aussagen zum Nutzungs- und Gefährdungspotential ermöglichen sollen.
Das Projekt "Erfassung der geologischen Struktur und Schalleintrag seismischer Wellen im Fernfeld" wird vom Umweltbundesamt gefördert und von Universität Kiel, Institut für Geowissenschaften, Abteilung Angewandte Geophysik durchgeführt. 1. Vorhabenziel Ziel des Teilprojektes der CAU/ IfG ist die Erfassung der geologischen Sedimentstruktur an drei Teststandorten von Offshore-Windkraftanlagen bis Gründungstiefe vor der Rammung sowie die Messung von durch die Rammung induzierten seismischen Wellen im Fernfeld mit Ozeanbodenseismometern (OBS). Strukturinformation und rammbegleitende Messungen sollen Rahmenbedingungen für die Modellierung des Körperschalls liefern und Abschätzungen/ Vorhersagemodelle über den Hydroschalleintrag im Fernfeld durch seismische Wellen ermöglichen. Als Ergebnis entsteht ein Untergrundmodell, das Tiefenpläne der geologischen Schichtgrenzen sowie die elasto-mechanischen Kenngrößen der geologischen Schichten enthält. 2. Arbeitsplanung Im Rahmen von Voruntersuchungen soll ein kombiniertes Verfahren aus hochauflösender Reflexionsseismik zur Strukturauflösung sowie Scholtewellenseismik zur Abschätzung des Schermoduls in der Umgebung jeder Gründungsposition durchgeführt werden. Des Weiteren sollen Messungen während der Rammung der OWEAs mit Ozeanbodenseismometern (OBS) durchgeführt werden, welche die Bodenbewegungen und den bodennahen Hydroschall im Fernfeld aufzeichnen. Durch die vom Projektpartner TUHH/ GBT geplanten Messungen ist es möglich, die Quellfunktion der Rammung zu bestimmen. Diese soll in zweidimensionale viskoelastische Finite-Differenzen-Modellierungen der seismischen Wellenausbreitung im Fernfeld eingebunden werden.