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  • 1
    Electronic Resource
    Electronic Resource
    Roller-bearing tectonic evolution of the Juan Fernandez microplate (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 571-576 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A combined GLORIA sidescan and Hydrosweep multi-narrow-beam sonar survey shows striking evidence for fan-shaped spreading systems, bounding pseudofaults and compression ridges associated with 90° of clockwise rotation of the Juan Fernandez microplate in the past 4 Myr. A quantitative analysis ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/356571a0
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Seismic imaging of Santorini: Subsurface constraints on caldera collapse and present-day magma recharge (2019)
    Elsevier
    In:  Earth and Planetary Science Letters, 514 . pp. 48-61.
    Details
    Publication Date: 2022-01-31
    Description: Highlights • There is a shallow low-velocity, high-porosity volume in the north-central caldera. • Vents of the first 3 LBA eruption phases correlate with this inner structure. • Inner collapse involved reverse faults, volcanic deposits, and/or rock fractures. • The low-density volume may have caused 2011-2012 inflation to localize beneath it. • The outer topographic caldera formed by relatively coherent down drop. Abstract Volcanic calderas are surface depressions formed by roof collapse following evacuation of magma from an underlying reservoir. The mechanisms of caldera formation are debated and predict differences in the evolution of the caldera floor and distinct styles of magma recharge. Here we use a dense, active source, seismic tomography study to reveal the sub-surface physical properties of the Santorini caldera in order to understand caldera formation. We find a ∼3-km-wide, cylindrical low-velocity anomaly in the upper 3 km beneath the north-central portion of the caldera, that lies directly above the pressure source of the 2011-2012 inflation. We interpret this anomaly as a low-density volume caused by excess porosities of between 4% and 28%, with pore spaces filled with hot seawater. Vents that were formed during the first three phases of the 3.6 ka Late Bronze Age (LBA) eruption are located close to the edge of the imaged structure. The correlation between older volcanic vents and the low-velocity anomaly suggests that this feature may be long-lived. We infer that collapse of a limited area of the caldera floor resulted in a high-porosity, low-density cylindrical volume, which formed by either chaotic collapse along reverse faults, wholesale subsidence and infilling with tuffs and ignimbrites, phreatomagmatic fracturing, or a combination of these processes. Phase 4 eruptive vents are located along the margins of the topographic caldera and the velocity structure indicates that coherent down-drop of the wider topographic caldera followed the more limited collapse in the northern caldera. This progressive collapse sequence is consistent with models for multi-stage formation of nested calderas along conjugate reverse and normal faults. The upper crustal density differences inferred from the seismic velocity model predict differences in subsurface gravitational loading that correlate with the location of 2011-2012 edifice inflation. This result supports the hypothesis that sub-surface density anomalies may influence present-day magma recharge events. We postulate that past collapses and the resulting topographical and density variations at Santorini influence magma focusing between eruptive cycles, a feedback process that may be important in other volcanoes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2019.02.033
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Heralds of a Future Eruption? Swarms of Microseismicity beneath the submarine Kolumbo Volcano indicate Opening of near-vertical Fractures exploited by ascending Melts (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-10
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    Revising the volume of the Minoan eruption (Santorini) based on new marine geophysical and sedimentological data (2022)
    Details
    Publication Date: 2024-01-08
    Description: With a maximum volume estimate of up to 86 km³ dense-rock equivalent (DRE), the Minoan Eruption is considered one of the largest Holocene eruptions. However, as most eruption products were deposited in the Mediterranean, previous volume estimates based on a limited database. We present new marine geophysical and sedimentological datasets allowing us to reassess the volume of the Minoan eruption in unprecedented detail. We combine high- resolution reflection seismic and P-wave tomography datasets with more than 40 marine sediment cores, constrained by X-ray computer-tomography (CT) scanning. The reflection seismic profiles indicate an ignimbrite volume of ~5.7 km³ DRE deposited on Santorini’s flanks, which is seven times smaller than previous estimates, while the P-wave tomography indicates ~5.5 km³ DRE of Minoan intra-caldera deposits, which is four times smaller than previous estimates. CT-guided analysis of the sediment cores allows us to differentiate two ash layers, which are separately integrated into ash deposit isopach maps and allows determine deposit porosities with high accurary. The combined ash volume of ~19.5 km³ DRE is in the same order as previous estimates. This yields a total eruption volume of ~31 km³ DRE. In addition, we use the new datasets to constrain the post-eruptive topography of the caldera and estimate the caldera collapse volume to be ~31.5 km³. The internal consistency of both independent approaches implies high confidence in our estimates, likely representing the most precise volume reconstruction of any major (M6.5+) volcanic eruption in the Holocene. Our analysis implies that the Minoan Eruption was smaller and produced significantly less ignimbrites than previous reconstructions indicated, while still causing a devastating tsunami. This highlights the significant tsunamigenic potential of submarine- emplaced ignimbrites
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 5
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    Heralds of Future Volcanism: Swarms of Microseismicity Beneath the Submarine Kolumbo Volcano Indicate Opening of Near‐Vertical Fractures Exploited by Ascending Melts (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable. Key Points Seismicity is clustered in a cone-shaped volume beneath Kolumbo; the cone's tip coincides with a melt reservoir at 2–4 km depth Seismicity swarms occupy nearby, yet different portions of the crust, ruling out an origin on a single fault Swarms were likely triggered by a combination of fluid pressure perturbations and redistribution of elastic stresses
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-11-19
    Description: Here we use SKS shear wave splitting observations from ocean-bottom seismometer data to infer patterns of mantle deformation beneath the Juan de Fuca plate and its adjoining boundaries. Our results indicate that the asthenosphere beneath the Juan de Fuca plate responds largely to absolute plate motion with an anisotropic layer developing rapidly near the ridge and persisting into the subduction zone. Geographically restricted deviations from this pattern indicate the presence of secondary processes. At discrete plate boundaries, such as the Blanco transform fault, seismic anisotropy is attributed to relative plate motion within a narrow zone (〈50 km). Beneath the deforming southern Gorda plate region—a diffuse plate boundary—splitting observations similarly suggest deformation dominated by relative motion between the rigid Juan de Fuca and Pacific plates but distributed over a broad zone (~200 km). Our results are inconsistent with toroidal flow around the southern edge of the subducting slab due to rollback, as suggested by onshore studies. Instead, reorganization of upper mantle flow associated with plate fragmentation seems to dominate the anisotropic signature of southern Cascadia.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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    PAPER CURRENT
  • 7
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    Next-generation seismic experiments - II: wide-angle, multi-azimuth, 3-D, full-waveform inversion of sparse field data (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-08
    Description: 3-D full-waveform inversion (FWI) is an advanced seismic imaging technique that has been widely adopted by the oil and gas industry to obtain high-fidelity models of P -wave velocity that lead to improvements in migrated images of the reservoir. Most industrial applications of 3-D FWI model the acoustic wavefield, often account for the kinematic effect of anisotropy, and focus on matching the low-frequency component of the early arriving refractions that are most sensitive to P -wave velocity structure. Here, we have adopted the same approach in an application of 3-D acoustic, anisotropic FWI to an ocean-bottom-seismometer (OBS) field data set acquired across the Endeavour oceanic spreading centre in the northeastern Pacific. Starting models for P -wave velocity and anisotropy were obtained from traveltime tomography; during FWI, velocity is updated whereas anisotropy is kept fixed. We demonstrate that, for the Endeavour field data set, 3-D FWI is able to recover fine-scale velocity structure with a resolution that is 2–4 times better than conventional traveltime tomography. Quality assurance procedures have been employed to monitor each step of the workflow; these are time consuming but critical to the development of a successful inversion strategy. Finally, a suite of checkerboard tests has been performed which shows that the full potential resolution of FWI can be obtained if we acquire a 3-D survey with a slightly denser shot and receiver spacing than is usual for an academic experiment. We anticipate that this exciting development will encourage future seismic investigations of earth science targets that would benefit from the superior resolution offered by 3-D FWI.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    PAPER CURRENT
  • 8
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    Tectonism and Its Relation to Magmatism Around Santorini Volcano From Upper Crustal P Wave Velocity (2019)
    In:  Journal of Geophysical Research: Solid Earth
    Details
    Publication Date: 2020-05-11
    Description: At extensional volcanic arcs, faulting often acts to localize magmatism. Santorini is located on the extended continental crust of the Aegean microplate and is one of the most active volcanoes of the Hellenic arc, but the relationship between tectonism and magmatism remains poorly constrained. As part of the Plumbing Reservoirs Of The Earth Under Santorini experiment, seismic data were acquired across the Santorini caldera and the surrounding region using a dense amphibious array of 〉14,300 marine sound sources and 156 short‐period seismometers, covering an area 120 km by 45 km. Here a P wave velocity model of the shallow, upper‐crustal structure (〈3‐km depth), obtained using travel time tomography, is used to delineate fault zones, sedimentary basins, and tectono‐magmatic lineaments. Our interpretation of tectonic boundaries and regional faults are consistent with prior geophysical studies, including the location of basin margins and E‐W oriented basement faults within the Christiana Basin west of Santorini. Reduced seismic velocities within the basement east of Santorini, near the Anydros and Anafi Basins, are coincident with a region of extensive NE‐SW faulting and active seismicity. The structural differences between the eastern and western sides of Santorini are in agreement with previously proposed models of regional tectonic evolution. Additionally, we find that regional magmatism has been localized in NE‐SW trending basin‐like structures that connect the Christiana, Santorini, and Kolumbo volcanic centers. At Santorini itself, we find that magmatism has been localized along NE‐SW trending lineaments that are subparallel to dikes, active faults, and regional volcanic chains. These results show strong interaction between magmatism and active deformation.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 9
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    Heralds of Future Volcanism: Swarms of Microseismicity Beneath the Submarine Kolumbo Volcano Indicate Opening of Near‐Vertical Fractures Exploited by Ascending Melts (2022)
    In:  Geochemistry Geophysics Geosystems (G3)
    Details
    Publication Date: 2022-11-09
    Description: The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 10
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    Swarms of Microseismicity Beneath the Submarine Kolumbo Volcano Indicate Opening of Near‐Vertical Fractures Exploited by Ascending Melts (2023)
    In:  Abstracts
    Details
    Publication Date: 2023-07-25
    Description: The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyse the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocentres and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable
    Type: info:eu-repo/semantics/conferenceObject
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