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  • 1
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (86 Blatt = 38 MB) , Illustrationen
    Series Statement: GEOMAR Report N.S. 34
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
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    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 122 (10). pp. 7927-7950.
    Publication Date: 2020-02-06
    Description: Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on-shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (∼1 year), resulting in a small number of usable records of teleseismic earthquakes. Here, we use OBSs deployed as mid-aperture array in the deep ocean (4.5-5.5 km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beam forming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8 km) of oceanic crust. Observations at single stations with thin sediments (300-400 m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of ∼70-80 km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at ∼410 km and ∼660 km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 3
    Publication Date: 2017-05-11
    Description: The Ionian Sea between Sicily and Calabria is known for its complex geological setting, as it is located at the convergence zone of the African and Eurasian plates. The seismogenic potential in this region is manifested by several high magnitude and disastrous earthquakes like the 1908 Messina Earthquake. Furthermore, the area is affected by intense volcanism like the Aeolian Island volcanos in the Tyrrhenian Sea and Europe’s largest active volcano, Mt Etna, sitting directly at the eastern coast of Sicily. During the last years, the possible presence of Subduction Tear Edge Propagator faults (STEP-faults) has been heavily debated. The main candidates for these faults are the Ionian Fault in the Northeast and the Alfeo-Etna Fault in the Southwest of the working area between Sicily and Calabria. Nevertheless, only little is known about near seafloor deformation zones and sedimentary processes in the Ionian Sea directly south of the Messina Strait. In order to obtain a better understanding of the sedimentary processes and the role of tectonics in the region, a new high-resolution 2D reflection seismic dataset was acquired during POS496 cruise during March – April 2016. In combination with existing additional seismic and bathymetric data, we mapped the area in terms of sedimentary and tectonic systems between Sicily and Calabria south of Messina Strait. The overall aim is to understand the relationship between tectonics and sedimentary processes in this complex geological area. The entire working area shows a variety of submarine channels, evolving from the central Messina Strait Canyon. In addition, large syn-tectonic south-north trending half grabens and sedimentary basins are imaged. The basins are filled by turbiditic- and contouritic deposits. Furthermore, several anticlines and negative flower structures were identified. We interpret these tectonic lineaments as the surface expression of deeply rooted transpressiveand transtensional fault systems. These fault systems with large strike-slip components could be near surface indicators for the proposed STEP Faults in the region. Not all morphological features like canyons/channels and structural heights follow significant tectonic lineaments. This indicates that some sedimentary features are decoupled from tectonics and are rather the expression of long lasting sedimentary processes like turbidity currents, mass transport events and bottom current activity.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
    Publication Date: 2017-12-07
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
    Publication Date: 2019-02-01
    Description: Our knowledge of the absolute S wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P wave polarization (apparent P wave incidence angle) of teleseismic events to investigate the S wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P wave incidence angle at the ocean bottom dependent on the half space S wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBS) to derive apparent S wave velocity profiles. These profiles are dependent on the S wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S wave velocity-depth models by a three step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S wave velocities. The apparent S wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 km and 0.9 km with S wave velocities between 0.7 km s−1 and 1.4 km s−1. The estimated total crustal thickness varies between 4 km and 10 km with S wave velocities between 3.5 km s−1 and 4.3 km s−1. We find a slight increase of the total crustal thickness from ∼5 km to ∼8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S wave velocities decrease from values around 5.5 km s−1 to 4.5 km s−1 towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S wave velocities for real and synthetic data to estimate S wave velocity-depth models.
    Type: Article , PeerReviewed
    Format: text
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  • 6
    Publication Date: 2016-12-01
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
    Publication Date: 2016-12-01
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
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    Unknown
    In:  [Poster] In: 2. Colloquium of Geophysical Signatures of Earthquakes and Volcanoes (2GSEV), 16.-18.05.2016, Santiago de Chile, Chile .
    Publication Date: 2016-12-01
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
    Publication Date: 2016-12-01
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2017-05-11
    Description: The largest and most active volcano in Europe is Mount Etna located on the east coast of Sicily. Over the last decades, extensive geodetic surveys focusing on the onshore flanks of Mount Etna have revealed instability of its eastern flank, which continuously moves seawards with displacement rates of up to 50 mm/yr. Catastrophic failure of the volcanic edifice could trigger a devastating tsunami in adjacent regions. The mechanism that is driven flank deformation is still under debate. Information on the dynamics of the submerged offshore domain might give new insights into the deformation mechanism. During the FS Poseidon cruise POS496 an acoustic geodetic network of five autonomous seafloor transponders was deployed across a dextral oblique transpressive fault north of Catania Canyon. This fault is interpreted as the offshore extension of the Tremestieri Fault System and as the offshore southern margin of the sliding sector. The seafloor geodetic transponders measure acoustic distances across the fault, absolute pressure and tilt for a period of up to 3 years. In addition, we deployed six ocean bottom seismometers to record local seismicity and three tiltmeters to monitor movement offshore Mount Etna.We present first results based on 5 months of geodetic data recorded from April to August 2016. The geodetic network is capable of resolving a minimum strike-parallel displacement of 25 mm and a minimum vertical throw of 1 mm. The data shows that surface fault movement appears to be less than these resolution minima for an observation period of 5 months. To date, the instruments continue collecting data and a longer time series will either confirm this observation or depict a constant rate of motion and/or episodic acceleration.
    Type: Conference or Workshop Item , NonPeerReviewed
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