Being to the world : an inquiry into philosophical implications of Hannah Arendt's political thought

Defence date: 28 March 2007Examining board: Prof. Peter Wagner, supervisor ; Prof. Christine Chwacscza ; Prof. Heidrun Friese, EHESS, Paris, and JWG University, Frankfurt, external co-supervisor ; Prof. Ugo Vlaisavljevic, University of SarajevoFirst made available online on 24 June 2015.The project inquires into Hannah Arendt's thinking of the political in order to develop from it a possible new thread towards a different philosophy beyond metaphysical legacy. Arendt's notion of human existence as always necessary doing to the world rather than just being is read here from her understanding of man as beginning. It is argued that, as such, it uncovers the existentialist dimension of Arendt's work, by and large neglected in Arendtian literature, while also influencing Arendt's understanding of the political as working freedom out of necessity and taking up of existence. This ultimately constitutes the unexplored contribution by Arendt to contemporary ontology: If ontology if to overcome and move beyond its metaphysical roots, it must ask political questions as the fundamental philosophical questions since it concerns the being that is always necessarily (in) doing. This reading of Arendt's project is founded upon the parallels of her thought with Heidegger's work that proceeds in the same philosophical direction. In order to understand and develop the implications of Arendt's thinking of the political in that direction, the project engages with Arendt's work on the source of action, which is interpreted here as a conceptual effort to overcome the metaphysical dualism of world. Arendt's theory of mind is analysed in relation to two fundamental principles of action, plurality and freedom, in order to argue that none of the three mind faculties - thinking, willing, judging - can generate action. The theory is then expanded through reference to the fragments on imagination in Arendt's writing, elaborated and developed in dialogue with Heidegger's and Castoriadis' work on the concept of imagination. Developing the concept of originary imagination as the source of action from these intuitions in Arendt's thought, the project uncovers the ontological fundament of opposition of Arendt's work to Heidegger's philosophy and establishes the ground to assert that Arendt's work offers an opening to post-metaphysical philosophy. While Heidegger's project is arrested by the notion of Dasein as being-in-the-world, unable to transcend givenness of existence and finally affirming it, Arendt puts forth the notion of human existence as primarily being to the world, always bringing about the new and resisting the givenness. This notion of human existence suggests that the fundamental questions of ontology ought to be political questions, the questions of doing rather than being

Variations in upper crustal structure due to variable mantle temperature along the Southeast Indian Ridge

There is a systematic variation in axial morphology and axial depth along the Southeast Indian Ridge (SEIR) with distance away from the Australian Antarctic Discordance, an area of cold uppermost mantle. Since spreading rate (72–76 mm/yr) and mantle geochemistry appear constant along this portion of the SEIR, the observed variations in axial morphology and axial depth are attributed to a gradient in mantle temperature. In this study, we report results from a multichannel seismic investigation of on-axis crustal structure along this portion of the SEIR. Three distinct forms of ridge crest morphology are found within our study area: axial highs, rifted axial highs, and shallow axial valleys. Axial highs have a shallow (~ 1500 m below seafloor (bsf)) magma lens and a thin (~ 300 m) layer 2A along the ridge crest. Rifted axial highs have a deeper (~ 2100 m bsf) magma lens and thicker (~ 450 m) layer 2A on-axis. Beneath shallow axial valleys, no magma lens is imaged, and layer 2A is thick (~ 450 + m). There are step-like transitions in magma lens depth and layer 2A thickness with changes in morphology along the SEIR. The transitions between the different modes of axial morphology and shallow structure are abrupt, suggesting a threshold-type mechanism. Variations in crustal structure along the SEIR appear to be steady state, persisting for at least 1 m.y. Portions of segments in which a magma lens is found are characterized by lower relief abyssal hills on the ridge flank, shallower ridge flank depths, and at the location of along-axis Mantle Bouguer Anomaly (MBA) lows. The long-wavelength variation in ridge morphology along the SEIR from axial high segments to the west to axial valley segments to the east is linked to the regional gradient in mantle temperature. Superimposed on the long-wavelength trend are segment to segment variations that are related to the absolute motion of the SEIR to the northeast which influence mantle melt production and delivery to the ridge

Upper crustal seismic structure along the Southeast Indian Ridge: Evolution from 0 to 550 ka and variation with axial morphology

The seismic structure of uppermost crust evolves after crustal formation with precipitation of alteration minerals during ridge-flank hydrothermal circulation. However, key parameters of crustal evolution including depth extent and rates of change in crustal properties, and factors contributing to this evolution remain poorly understood. Here, long-offset multichannel seismic data are used to study the evolution of seismic layer 2A and uppermost 2B from 0 to 550 ka at three segments of the intermediate spreading rate Southeast Indian Ridge. The segments differ in on-axis morphology and structure with crustal magma bodies imaged at axial high and rifted high segments P1 and P2, but not at axial valley segment S1 and marked differences in thermal conditions within the upper crust are inferred. One-dimensional travel time modeling of common midpoint supergathers is used to determine the thickness and velocity of layer 2A and velocity of uppermost 2B. At all three segments, layer 2A velocities are higher in 550 ka crust than on-axis (by 7–14%) with the largest increases at segments P1 and P2. Velocities increase more rapidly (by 125 ka) at P1 with spatial variations in velocity gradients linked to location of the underlying crustal magma body. We attribute these differences in crustal evolution to higher rates of fluid flow and temperatures of reaction at these ridge segments where crustal magma bodies are present. Layer 2A thickens off-axis at segments P1 and P2 but not at S1; both off-axis volcanic thickening and downward propagation of a cracking front linked to the vigor of axial hydrothermal activity could contribute to these differences. In zero-age crust, layer 2B velocities are significantly lower at segments P1 and P2 than S1 (5.0, 5.4, and 5.8 km/s respectively), whereas similar velocities are measured off-axis at all segments (5.7–5.9 km/s). Lower on-axis 2B velocities at segments P1 and P2 can be partly attributed to thinner layer 2A, with lower overburden pressures leading to higher porosities in shallowest 2B. However, other factors must also contribute. Likely candidates include subaxial deformation due to magmatic processes and enhanced cracking with axial hydrothermal activity at these segments with crustal magma bodies

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Nature Geoscience 10 (2017): 864-870, doi:10.1038/ngeo3050.Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.This research was funded by the US NSF

Evolution of seismic layer 2B across the Juan de Fuca Ridge from hydrophone streamer 2-D traveltime tomography

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q05009, doi:10.1029/2010GC003462.How oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the Earth's interior and the oceans. Although considerable work has been done characterizing the evolution of seismic layer 2A, there has been little analysis of the processes that affect layer 2B after formation. Here we present high-resolution 2-D tomographic models of seismic layer 2B along ∼300 km long multichannel seismic transects crossing the Endeavour, Northern Symmetric, and Cleft segments of the Juan de Fuca Ridge. These models show that seismic layer 2B evolves rapidly following a different course than layer 2A. The upper layer 2B velocities increase on average by 0.8 km/s and reach a generally constant velocity of 5.2 ± 0.3 km/s within the first 0.5 Myr after crustal formation. This suggests that the strongest impact on layer 2B evolution may be that of mineral precipitation due to “active” hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber. Variations in upper layer 2B velocity with age at time scales ≥0.5 Ma show correlation about the ridge axis indicating that in the long term, crustal accretion processes affect both sides of the ridge axis in a similar way. Below the 0.5 Ma threshold, differences in 2B velocity are likely imprinted during crustal formation or early crustal evolution. Layer 2B velocities at propagator wakes (5.0 ± 0.2 km/s), where enhanced faulting and cracking are expected, and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2B. Analysis of the layer 2B velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2B velocities, respectively. Additionally, the distance between present up-flow and down-flow zones is related to the amount of sediment cover because, as sediment cover increases and basement outcrops become covered, direct pathways from the igneous basement through the seafloor are cut off, forcing convective cells to find alternate paths.This research was supported by National Science Foundation grants OCE0002488 and OCE0648303 to S.M.C. and M.R.N., NSERC Discovery grant to M.R.N., and a Bruce C. Heezen Graduate Research Fellowship (Office of Naval Research grant N00014‐02‐1‐0691) to K.R.N

Temperature and salinity observations with high lateral resolution using acoustic data in the Gulf of Cadiz, NE Atlantic Ocean

European Geosciences Union General Assembly 2015 (EGU2015), 12-17 April 2015, Vienna, Austria.-- 1 pageWe present a methodology for inverting temperature and salinity from time and space-coincident acoustic reflectivity and XBT data. This method recovers low frequency content ( 10 Hz) from acoustic reflectivity. Afterwards, maps of temperature and salinity are calculated from impedance using the GSW equations of state and an empirical T-S relation. Acoustic data allows to recover the main physical parameters of the ocean along lateral sections of hundreds of km, covering all the full-depth water column and with vertical and lateral resolutions of 10 m and 100 m, respectively. This method was applied in the Gulf of Cadiz, NE Atlantic Ocean to recover the main physical oceanographic parameters in the ocean with accuracies of δTsd = 0.1 C, δSsd = 0.09 and δsd = 0.02kg/m3 for temperature, salinity and potential density. Inverted temperature anomalies reveal baroclinic thermohaline fronts with intrusions.The observations support a mix of thermohaline features created by both double-diffusive and isopycnal stirring mechanismsPeer Reviewe

New insights into the rift to drift transition across the northeastern Nova Scotian margin from wide-angle seismic waveform inversion and reflection imaging

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(12), (2021): e2021JB022201, https://doi.org/10.1029/2021JB022201.Sparse wide-angle seismic profiling supported by coincident reflection imaging has been instrumental for advancing our knowledge about rifted margins. Nevertheless, features of critical importance for understanding rifting processes have been poorly resolved. We derive a high-resolution velocity model by applying full waveform inversion to the dense OETR-2009 wide-angle seismic profile crossing the northeastern Nova Scotian margin. We then create a coincident reflection image by prestack depth migrating the multichannel seismic data. This allows for the first detailed interpretation of the structures related to the final stages of continental breakup and incipient oceanic accretion at the Eastern North America Margin. Our interpretation includes a hyperextended continental domain overlying partially serpentinized mantle, followed by a 10-km-wide domain consisting of a continental block surrounded by layered and bright reflectors indicative of magmatic extrusions. A major fault, representing the continent-ocean boundary, marks a sharp seaward transition to a 16-km-wide domain characterized by smoother basement with chaotic reflectors, where no continental materials are present and a 3-km-thick embryonic oceanic crust overlying partially serpentinized mantle is created by the breakup magmatism. Further seaward, thin oceanic crust overlies the serpentinized mantle suggesting magma-poor oceanic spreading with variable magma supply as determined from variable basement topography, 2–4 km thick volcanic layer, and magnetic anomalies. Our results demonstrate that magmatism played an important role in the lithospheric breakup of the area crossed by the OETR-2009 profile. Considering that the northeastern Nova Scotian margin has been classified as amagmatic, large margin-parallel variations in magma supply likely characterize a single rift segment.H. Jian was supported by the Ocean Frontier Institute International Postdoctoral Fellowship at Dalhousie University and NSF grant OCE-2001012

Synthetic Modeling for an Acoustic Exploration System for Physical Oceanography

10 pages, 6 figures, 1 tableMarine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth¿s subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10¿100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 dB relative to 1 ¿Pa at 1 m with a frequency content of 20¿100 Hz and a relatively short 500-m-long streamer with 100 channels. This study exemplifies through numerical simulations that the 5-s-long chirp source can reduce the peak of the pressure signal by 26 dB with respect to equivalent air gun¿based sources by spreading the energy in time, greatly reducing the impact to marine life. Additionally, the proposed system could be transported and installed in midsize oceanographic vessels, opening new horizons in acoustic oceanography researchThe first author’s work has been supported by the European Commission through Marie Curie Actions FP7-PEOPLE-2010-IOF-271936 and FP7-PEOPLE-2012-COFUND-600407. This work has been done in the framework of the Spanish project POSEIDON (CTM2010-25169) and the Italian National Flagship Programme RITMARE (Programma Nazionale della Ricerca 2011-2013 MIUR). We want to acknowledge the team of GO project funded by the EU (015603-GO-STREP)Peer Reviewe

Recent seismic studies at the East Pacific Rise 8°20'–10°10'N and Endeavour Segment : insights into mid-ocean ridge hydrothermal and magmatic processes

Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 1 (2012): 100–112, doi:10.5670/oceanog.2012.08.As part of the suite of multidisciplinary investigations undertaken by the Ridge 2000 Program, new multichannel seismic studies of crustal structure were conducted at the East Pacific Rise (EPR) 8°20'–10°10'N and Endeavour Segment of the Juan de Fuca Ridge. These studies provide important insights into magmatic systems and hydrothermal flow in these regions, with broader implications for fast- and intermediate-spreading mid-ocean ridges. A mid-crust magma body is imaged beneath Endeavour Segment underlying all known vent fields, suggesting that prior notions of a tectonically driven hydrothermal system at this site can be ruled out. There is evidence at both sites that the axial magma body is segmented on a similar 5–20 km length scale, with implications for the geometry of high-temperature axial hydrothermal flow and for lava geochemistry. The new data provide the first seismic reflection images of magma sills in the crust away from the axial melt lens. These off-axis magma reservoirs are the likely source of more-evolved lavas typically sampled on the ridge flanks and may be associated with off-axis hydrothermal venting, which has recently been discovered within the EPR site. Clusters of seismic reflection events at the base of the crust are observed, and localized regions of thick Moho Transition Zone, with frozen or partially molten gabbro lenses embedded within mantle rocks, are inferred. Studies of the upper crust on the flanks of Endeavour Segment provide new insights into the low-temperature hydrothermal flow that continues long after crustal formation. Precipitation of alteration minerals due to fluid flow leads to changes in P-wave velocities within seismic Layer 2A (the uppermost layer of the oceanic crust) that vary markedly with extent of sediment blanketing the crust. In addition, intermediate-scale variations in the structure of Layers 2A and 2B with local topography are observed that may result from topographically driven fluid upflow and downflow on the ridge flanks.This research was supported by NSF OCE grants 0002488, 0002551, 0648303, 0648923, 0327872 and 0327885

Vp/Vs ratio of incoming sediments off Cascadia subduction zone from analysis of controlled-source multicomponent OBS records

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(6), (2020): e2019JB019239, doi:10.1029/2019JB019239.P‐to‐S‐converted waves observed in controlled‐source multicomponent ocean bottom seismometer (OBS) records were used to derive the Vp/Vs structure of Cascadia Basin sediments. We used P‐to‐S waves converted at the basement to derive an empirical function describing the average Vp/Vs of Cascadia sediments as a function of sediment thickness. We derived one‐dimensional interval Vp/Vs functions from semblance velocity analysis of S‐converted intrasediment and basement reflections, which we used to define an empirical Vp/Vs versus burial depth compaction trend. We find that seaward from the Cascadia deformation front, Vp/Vs structure offshore northern Oregon and Washington shows little variability along strike, while the structure of incoming sediments offshore central Oregon is more heterogeneous and includes intermediate‐to‐deep sediment layers of anomalously elevated Vp/Vs. These zones with elevated Vp/Vs are likely due to elevated pore fluid pressures, although layers of high sand content intercalated within a more clayey sedimentary sequence, and/or a higher content of coarser‐grained clay minerals relative to finer‐grained smectite could be contributing factors. We find that the proto‐décollement offshore central Oregon develops within the incoming sediments at a low‐permeability boundary that traps fluids in a stratigraphic level where fluid overpressure exceeds 50% of the differential pressure between the hydrostatic pressure and the lithostatic pressure. Incoming sediments with the highest estimated fluid overpressures occur offshore central Oregon where deformation of the accretionary prism is seaward vergent. Conversely, landward vergence offshore northern Oregon and Washington correlates with more moderate pore pressures and laterally homogeneous Vp/Vs functions of Cascadia Basin sediments.This research was funded by National Science Foundation (NSF) Grant OCE‐1657237 to J. P. C, OCE‐1657839 to A. F. A. and S. H., and OCE‐1657737 to S. M. C. Data used in this study were acquired with funding from NSF Grants OCE‐1029305 and OCE‐1249353. Data used in this research were provided by instruments from the Ocean Bottom Seismic Instrument Center (http://obsic.whoi.edu, formerly OBSIP), which is funded by the NSF. OBSIC/OBSIP data are archived at the IRIS Data Management Center (http://www.iris.edu) under network code X6 (https://doi.org/10.7914/SN/X6_2012). Data processing was conducted with Emerson‐Paradigm Software package Echos licensed to Woods Hole Oceanographic Institution under Paradigm Academic Software Program and MATLAB package SeismicLab of the University of Alberta, Canada (http://seismic-lab.physics.ualberta.ca), under GNU General Public License (MATLAB® is a registered trademark of MathWorks).2020-11-2