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Analysis of NGR Spectra from Deep-Sea Sediments in the Philippine Sea, Site 1201
No full textNatural gamma ray measurements are made routinely during core logging using the physical property multisensor track. The instrument provides a measure of the natural decay of radioactive elements in the core, expressed in counts per second, which is generally used as a proxy for the clay content of nonmarginal marine sediments. At Site 1201 spikes of increased gamma ray emissions, up to six times the average for the entire core over depth intervals on the order of 20–50 cm, are observed from the sediments within 50 m of the basement contact. The spikes show a strong correlation with sediment color variations, coinciding with red/brown layers within otherwise green/gray-colored sediments. In this paper, the gamma ray spectra obtained from 21 measurements using a 4-hr counting period are analyzed to obtain the absolute concentration of the radioactive elements K2O, U, and Th in both the intervals with spikes and the intervals with relatively low count rates. In addition, the concentration of these elements is estimated using the spectra obtained from the routine 20-s counting period measurements and which, although exhibiting a great deal of scatter due to the high statistical uncertainty in the original measurements, are roughly similar to those obtained from the 4-hr counting period. Baseline concentrations for U (1 ppm) and Th (5 ppm) match published averages for the amount present in deep-sea clays; the peak concentrations measured correspond to an additional concentration of 100%–200%. The results are compared to those from downhole logging and shipboard inductively coupled plasma–atomic emission spectrometry measurements. The gamma ray spectra results do not support postdepositional fluid flow through the sediment as the source of the enrichment of radioactive elements. It is more likely that the spikes in the gamma ray emissions are simply the result of interbedding sediments from two different sources, one with relatively high concentrations of K2O, U, and Th
Seismic constraints on the three-dimensional geometry of low-angle intracrustal reflectors in the Southern Iberia Abyssal Plain
No full textSeveral lines of evidence suggest that simple shear rifting of the continental crust, in the formof low-angle detachment faulting, occurred during the final stages of continental breakupbetween West Iberia and the Grand Banks. The primary evidence for such faulting is theoccurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean–continent transition zone. Here we present a series of intersecting, depth migrated seismicreflection profiles that image one such reflector, the H-reflector, located on the southern edgeof Galicia Bank. ‘H’ lies beneath several boreholes drilled during ODP Legs 149 and 173,in a region where the oceanward extent of extended continental crust steps at least 150 kmwestward from its location in the southern Iberia Abyssal Plain to its location off the relativelyshallow Galicia Bank. In our profiles ‘H’ appears to define a surface that extends over a regionof at least 200 km2 and that dips down ?19? to the north, towards Galicia Bank. The profilesshow that a close affinity exists between ‘H’ and the most seaward continental crust. Based ongeophysical data and ODP drilling results, we infer that the basement above ‘H’ is composedof continental crust deformed by extensional faults into a series of wedge-shaped blocks andthin slivers. These basement wedges have a complex 3-D geometry. ‘H’ rises to the basementsurface on a number of the seismic profiles and appears to define locally the oceanward extentof continental fault blocks
RV Sonne Cruise 198-1, 03 May-14 Jun 2008. Singapore - Merak, Indonesia
Full text linkAll plate boundaries are divided into segments - pieces of fault that are distinct from one another, either separated by gaps or with different orientations. The maximum size of an earthquake on a fault system is controlled by the degree to which the propagating rupture can cross the boundaries between such segments. A large earthquake may rupture a whole segment of plate boundary, but a great earthquake usually ruptures more than one segment at once. Earthquakes offshore of Sumatra on December 26th 2004 (MW=9.3) and March 28th 2005 (MW=8.7) ruptured, respectively, 1200-1300 km and 300-400 km of the subduction boundary between the Indian-Australian plate and the Burman and Sumatra blocks. Rupture in the 2004 event started at the southern end of the fault segment, and propagated northwards. The observation that the slip did not propagate significantly southwards in December 2004, even though the magnitude of slip was high at the southern end of the rupture strongly suggests a barrier at that place. Maximum slip in the March 2005 earthquake occurred within ~100 km of the barrier between the 2004 and 2005 ruptures, confirming both the physical importance of the barrier, and the loading of the March 2005 rupture zone by the December 2004 earthquake.Cruise SO198-1, from Singapore to Merak between 3rd May and 14th June 2008 is the first of three cruises, funded by the Natural Environment Research Council (NERC), which will form a coherent set of geophysical observations in the source regions of the 2004 and 2005 great Sumatra earthquakes. Arrays of 50 ocean-bottom seismometers (OBS) were deployed at each of two locations – between the 2004 and 2005 ruptures, and at the southern end of the 2005 rupture - to record shots from a large-capacity airgun array. Approximately 7 days ofcontinuous airgun shooting at 60s interval was completed at each location. 10 OBS were reconfigured for earthquake recording and deployed with a planned retrieval in early 2009.Gravity, Parasound, and swath bathymetry data were recorded continuously while in the permitted area, with magnetic field data recorded throughout the airgun shooting, and 101 XBT casts taken at the OBS deployment locations
The peridotite ridge province in the southern Iberia Abyssal Plain: seismic constraints revisited
No full textThe west Iberia margin has become the type example of a magma-starved margin in which extension during breakup led to the exhumation of mantle rocks apparently over a broad area. Much of our understanding of this process is based on geophysical and drilling data from the southern Iberia Abyssal Plain, where the seaward part of the region of exhumed mantle is comprised of a series of margin-parallel basement ridges. Here we analyse wide-angle and normal incidence seismic data from a series of intersecting profiles across this peridotite ridge province and develop a three-dimensional picture of its structure. Using these seismic data, we infer a location and age (magnetic anomaly M1; 125-127?Ma) of first-formed oceanic crust in this region that are consistent with Ocean Drilling Program data and data from the conjugate margin. We infer that the peridotite ridge province is about 70?km wide with strong serpentinization (>75%) at the top of basement reducing to much lower degrees (< 25%) around 2?km below. We map the geometry of some prominent reflectors on the landward margin of the peridotite ridge province that likely represent detachment faults and show that one of these has a domal structure similar to that of detachment faults at slow- to ultra-slow-spreading mid-ocean ridges
Anomalous melt production after continental breakup in the southern Iberia Abyssal Plain
No full textRV Sonne Cruise 198-2, 18 Jun-01 Aug 2008. Merak, Indonesia - Merak, Indonesia
Full text linkAll plate boundaries are divided into segments - pieces of fault that are distinct from one another, either separated by gaps or with different orientations. The maximum size of an earthquake on a fault system is controlled by the degree to which the propagating rupture can cross the boundaries between such segments. A large earthquake may rupture a whole segment of plate boundary, but a great earthquake usually ruptures more than one segment at once.Earthquakes offshore of Sumatra on December 26 2004 (MW=9.3) and March 28 2005 (MW=8.7) ruptured, respectively, 1200-1300 km and 300-400 km of the subduction boundary between the Indian-Australian plate and the Burman and Sumatra blocks. Rupture in the 2004 event started at the southern end of the fault segment, and propagated northwards. The observation that the slip did not propagate significantly southwards in December 2004, even though the magnitude of slip was high at the southern end of the rupture strongly suggests a barrier at that place. Maximum slip in the March 2005 earthquake occurred within ~100 km of the barrier between the 2004 and 2005 ruptures, confirming both the physical importance of the barrier, and the loading of the March 2005 rupture zone by the December 2004 earthquake. Cruise SO198-2, from Merak to Merak between 18 June and 01 August 2008 is the second of three cruises, funded by the Natural Environment Research Council (NERC), which will form a coherent set of geophysical observations in the source regions of the 2004 and 2005 great Sumatra earthquakes. This cruise collected seismic reflection (MCS) profiles at SB1 and SB2 with the following objectives:1. To image the geometry and nature of the downgoing slab from the trench to 30-40 km depth within the forearc2. To image faults within the over-riding plate responsible for the development of the accretionary wedge3. To provide a set of shots that will calibrate the array of ocean-bottom seismometers deployed on cruise SO198-1, and be recorded by the land seismometer array established by a different part of the consortium.Cruise SO198-2 also included nine days of ship time funded by the United States National Science Foundation to investigators from the University of Texas Institute for Geophysics (UTIG). This allied study targeted the subject of rupture pathways, with a focus was on how the earthquake rupture propagates updip through the accretionary prism to ultimately move the seafloor and create the tsunami.Approximately 5000km of multichannel seismic reflection data were collected during the cruise, as well as continuous recording of gravity, magnetics, Parasound and swath bathymetry data while in the permitted area
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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