1,720,986 research outputs found
Geomorphology of the 26 December 2004 Indian Ocean Earthquake Rupture Zone – Results from the First Seafloor Survey Onboard the HMS Scott, 2005
No full textThe 26 December 2004 Mw 9.3 Sumatra to Andaman Islands subduction zone earthquake was the second largest earthquake recorded. The tsunami generated by the earthquake caused the loss of ~300,000 lives and devastation of many Indian Ocean coastal communities. The Royal Navy's HMS Scott conducted a multibeam bathymetric survey over the rupture zone during January and February 2005. An area of ~40000 km2 was surveyed during the three week expedition using a 12 kHz, 361 beam hull-mounted Sass IV sonar. This study is the first time a high resolution deep-water seafloor survey has been carried out so soon after a major plate-boundary subduction zone earthquake. Existing geophysical data in the earthquake rupture zone are rare and therefore the general subduction zone structure is poorly known. Data were collected along 400km of the southern and intial part of the rupture zone offshore Sumatra, including the plate boundary and lower accretionary wedge, the southern termination of the earthquake rupture which represents a probable major segment boundary, and parts of the forearc basin and outer arc high system.
Initial results reveal the geomorphology of the seafloor and clues to the tectonic and sedimentary processes controlling this morphology during periods of thousands to millions of years of plate convergence. The gradient of the seafloor from the plate boundary (deformation front) where the two plates collide across the accretionary wedge folds is very steep – rising ~4000 m over a distance of about 20 km in places. These steep slopes and continuing uplift due to collision augmented by earthquake shaking leads to extensive slope failure and submarine landsliding. The seafloor of the accretionary wedge folded ridges is therefore heavily eroded in places. At the deformation front, a few coherent landslides produce angular blocks which have slid onto the undeformed Indian plate. The youngest of these features has angular coherent blocks and a steep landslide headwall scarp. Sediment from these landslides and slumps is transported into neighbouring basins by short canyon and channel systems. No evidence was found of recent landslides large enough to contribute significantly to the tsunami generated in 2004.
Fold ridges of the accretionary wedge are easily identified in the multibeam images. The youngest of these fold ridges at the deformation front where the plates meet are relatively uneroded and only a few hundred metres high. These ridges will have formed over thousands of years. The quality of the data allows small tectonic features to be identified at the base of these ridges. Some of these features may be formed by fault movement during earthquakes such as the event of 2004. The southern part of the HMS Scott survey overlaps with the rupture zone of the Mw 8.7 earthquake that occurred on March 28 2005, thus presenting the potential for "before" and "after" surveys to better understand how some of these structures may form and be modified during major plate boundary events
Seafloor morphology of the Sumatran subduction zone: surface rupture during megathrust earthquakes?
No full textHigh-resolution multibeam bathymetry data from the Sumatran subduction zone reveal the regional and local morphology, including small-scale fault-related features and landslides that may be linked to earthquakes in the recent geological past. The accretionary prism is steeply sloped and pervasively eroded, with evidence of unusual landward vergence (seaward fault dip) of the frontal thrusts. Small-scale (5–100 m height) fault scarps, folds, and troughs are common along the seaward edge of the frontal thrust at the deformation front. A model of back-thrust fault slip or bending moment folding during plate-boundary slip, such as during the 2004 M9.2 megathrust earthquake, can explain the position of these features on the seaward fold limb of a seaward-dipping thrust. We infer that in major Sumatran (and other similar settings) plate-boundary earthquakes, coseismic surface rupture may occur at the prism toe
Recent seafloor deformation at the 26 December 2004 Indian Ocean earthquake rupture zone: results from the HMS Scott 2005 survey (abstract of paper presented at the EGU General Assembly 2005, Vienna, 24-29 April 2005)
No full textThe 26 December 2004 Mw 9.3 Sumatra to Andaman Islands subduction zone earth-quake was the second largest earthquake recorded. The tsunami generated by the earthquake caused the loss of ~300,000 lives and devastation of many Indian Ocean coastal communities. The Royal Navy's HMS Scott conducted a bathymetric survey over the rupture zone during early 2005. This is the first time a high resolution deep-water seafloor survey has been carried out so soon after an earthquake of this magnitude. Existing geophysical data in the earthquake rupture zone are rare and therefore the general subduction zone structure is poorly known. Data were collected in the southern and intial part of the rupture zone offshore Sumatra, including the plate boundary and lower accretionary wedge, the southern termination of the earthquake rupture and probable segment boundary, and parts of the forearc basin and outer arc high system. The data reveal the gross morphology of the margin and details of the structural geometry and ongoing sedimentary processes. Initial results indicate a number of youthful tectonic and slope failure features within the lower part of the accretionary wedge
Mass wasting processes : offshore Sumatra
Get PDFEarthquakes are a commonly cited mechanism for triggering submarine landslides that have the potential to generate locally damaging tsunamis. With measured runups of over 35 metres in northern Sumatra from the December 26th 2004 tsunami source, these runups might be expected to be due, in part, to local submarine landslides. Mapping of the convergent margin offshore of Sumatra using swath bathymetry, single channel seismic and seabed photography reveals that seabed failures are common, but mainly small-scale, and composed of blocky debris avalanches and sediment flows. These failures would have contributed little to local tsunami runups. Large landslides are usually formed where there is significant sediment input. In the instance of Sumatra, most sediment is derived from the oceanic plate, and there is little sediment entering the system from the adjacent land areas. Input from the oceanic source is limited because of the diversion of sediment entering the subduction system off of Sumatra, that is attributed to collision between the Ninetyeast ridge and the Sunda Trench at approximately 1.5 million years ago
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
