Description: Seismic investigations across the convergent Sunda margin off Indonesia provide a detailed image of the crustal architecture of the Sunda plate boundary. The combined analysis and interpretation of wide-angle and reflection seismic data along two coincident profiles across the subduction zone are complemented by additional lines within the forearc domain, which yield some three-dimensional (3-D) constraints on the velocity-depth structure across the margin. A detailed cross section of the subduction zone is presented, which is confirmed by supplementary gravity modeling. The Sunda convergence zone is a prime example of an accretionary margin, where sediment accretion has led to the formation of a massive accretionary prism, with a total width of 〉110 km between the trench and the forearc basin. It is composed of a frontal wedge which documents ongoing accretion and a fossil part behind the present backstop structure which constitutes the outer high. Moderate seismic velocities derived from wide-angle modeling indicate a sedimentary composition of the outer high. The subducting oceanic slab is traced to a depth of almost 30 km underneath the accretionary prism. The adjacent forearc domain is characterized by a pronounced morphological basin which is underlain by a layer of increased seismic velocities and a shallow upper plate Moho at 16 km depth. We speculate that remnant fragments of oceanic crust might be involved in the formation of this oceanic-type crust found at the leading edge of the upper plate beneath the forearc basin.

Description: Marine seismic wide-angle data acquisition and earthquake seismology observations are at the verge of a quantum leap in data quality and density. Advances in micro-electronic technology facilitates the construction of instrumcnts that enable large data volumes to be collected and that are small and cheap enough so that large numbers can be built and operated economically. The main improvements are a dramatic decrease of power consumption ( 〈 250 m W) and increase in clock stability ( 〈 0.05 ppm}. Several scenarios for future experiments arc discussed in this contrihution

Description: A seismic wide-angle section offshore Costa Rica is presented across the boundary between oceanic crust generated at the East Pacific rise (EPR) and at the Galápagos spreading center (GSC) as indicated by magnetic anomalies. This suture, where the Farallon plate broke up ∼23 Ma ago, is marked by pronounced velocity variations throughout the crust including a low-velocity body in the lower crust. This body is well constrained by refracted waves above the inversion zone and by strong PmP reflections from its lower boundary. The distinctness of this body and the local gravity field point to an igneous intrusion rather than serpentinized rock. Typical oceanic crust is found adjacent to the suture zone.

Description: Im Rahmen der deutsch-französischen Kooperation standen auf der SONNE Fahrt SO159 vom 21.08. bis 17.09.2001 seismische Weitwinkelmessungen auf dem Carnegie Rücken und am ecuadorianischen Kontinentalrand im Vordergrund. Über erste Ergebnisse wird berichtet. Der Carnegie Rücken wurde auf zwei nahezu Nord-Süd verlaufenden Profilen untersucht. Das westliche Profil quert den Rücken an einer Lokation, wo dieser morphologisch wenig ausgeprägt ist. Das östliche Profil liegt unmittelbar vor der Grabenachse, hier ragt der Rücken bis auf 800 m Wassertiefe empor. Auf beiden Profilen wurden Ozeanbodenseismometer (OBS) und –hydrophone (OBH) im Abstand von 8 bis 9 km ausgelegt, die Airgunschüsse können bis in Entfernungen von über 100 km beobachtet werden und erlauben es, die Krustenstruktur und den obersten Mantel abzubilden. Auf beiden Profilen wird der Übergang von normaler Ozeankruste zu der verdickten Kruste des aseismischen Rückens deutlich. Die interne Struktur des Carnegie Rückens wird maßgeblich durch eine verdickte Unterkruste bestimmt. Die Krustenmächtigkeit beträgt 16 km auf dem westlichen Profil und 28 km im Osten. Die bathymetrischen Vermessungen des Carnegie Rückens mit dem neuen SIMRAD Fächerecholot zeigen den Rücken als stark asymetrische Aufwölbung mit einer steil einfallenden nördlichen und einer leicht geneigten südlichen Flanke, die von lokalen Seamounts durchdrungen wird. Im Golf von Guayaquil wurden entlang existierender Reflexionsprofile Weitwinkeldaten gewonnen. Hier ist die flach abtauchende ozeanische Kruste der Nazca Platte zu erkennen. Bis zu 6 km mächtige Sedimente werden im Forearc Becken angetroffen. Das Basement des erodierten früheren Kontinentalrandes reicht bis dicht an die Grabenachse, eine Zone erniedrigter Geschwindigkeiten oberhalb der abtauchenden ozeanischen Platte kann als Hinweis auf subduzierte Sedimente angesehen werden.

Description: The paper presents an overview of recent seafloor long-term single-frame multiparameter platform developed in the framework of the European Commission and Italian projects starting from the GEOSTAR prototype. The main features of the different systems are described as well as the sea missions that led to their validation. The ORION seafloor observatory network recently developed, based on the GEOSTAR-type platforms and engaged in a deep-sea mission at 3300 m w.d. in the Mediterranean Sea, is also described

Description: Introduction Since the discovery of ‘bright spots’ associated with hydrocarbon deposits, ever increasing interest in determining lithological subsurface parameters has been a driving force for technological development in the hydrocarbon exploration industry. Quantification of lithological parameters is of utmost importance for reservoir prediction and monitoring. Amongst various attempts to determine these, attribute analysis of pwave data and the direct observation of shear wave data are the most visible and successful methods applied. The direct observation of shear waves in the marine environment has been attempted by several means, mainly using ocean bottom cables (OBC) that have three-component geophones (3C) and a hydrophone in addition (thus 4C in total). Some manufacturers offer two component geophones with only one horizontal component. These cables are laid out on the seafloor, sometimes even buried using specialized tools like ROVs (remotely operated vehicles). Data transfer is through the cables as in streamers or land operations, recording is made on a boat or platform where the cable terminates. Geophones are housed in tubes with a self-levelling gimballed mounting system, damped by a viscous fluid. This technique is regarded as proven technology and has been widely accepted. Especially in production areas with many man-made obstacles, this technique also offers a safe operation, and is especially suitable for monitoring purposes (4D–4C seismic). Any desired geometry and density of receivers can be laid out. Direct shear wave observations have been made by several academic institutions, both for active seismic exploration as well as for passive seismological monitoring of earthquakes. These institutions have built ocean bottom seismometers (OBS), which are also four component, two sensor instruments. Unlike OBC, they are autonomously lowered to the seafloor, record within specified time windows, and are later brought back to the surface. Amongst the various instruments designed over the past decades is the OBS range built at GEOMAR, which – due to its modular design – has been used for a wide range of applications.