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Seismotectonics of the Andaman-Nicobar plate boundary and evaluation of the 2004 deformational and depositional features towards assessing past tsunamigenic earthquakes.
Get PDFSeismotectonics Of The Andaman-Nicobar Plate Boundary And Evaluation Of 2004 Deformational And Depositional Features Towards Assessing Past Tsunamigenic Earthquakes
Get PDFTsunami hazards were greatly underestimated along the coasts of countries bordering the northeastern Indian Ocean until the occurrence of the 26 December 2004, Mw 9.2 earthquake and its ensuing tsunami. Sourced off the coast of northern Sumatra, on the plate boundary between the Indo-Australian and Eurasian plates, the rupture of the 2004 earthquake propagated ~1300 km northward. The magnitude of this earthquake and the reach of its tsunami exceeded all known precedents, based on instrumental and historic records. The coseismic deformational and post-tsunami depositional features facilitated opportunities to conduct tsunami geology studies along the coasts of countries bordering the Indian Ocean. Several questions are being posed, the answers of which have implications for tsunami hazard assessment. How did this plate boundary behave prior to and after the great earthquake? Was the 2004 earthquake the first of its kind on the Sumatra-Andaman plate boundary? If it had a predecessor, when did it occur and was it a true predecessor in terms of its rupture dimensions and tsunamigenic potential? What types of depositional evidence are preserved and how can we use them to develop the history of past tsunamigenic earthquakes? Researchers are exploring the affected regions and using the imprints left by the 2004 event, to address these questions.
There are two components to this study: one, a seismotectonic analysis of the region from the perspective of plate driving forces and their relative roles in the interseismic and post-seismic phases. This study uses global data catalogs like the NEIC PDE (National Earthquake Information Centre Preliminary Determination of Epicenters) and the Global Centroid Moment Tensor (CMT) solutions for earthquake source parameters to understand the along-strike variations in seismicity patterns before and after the 2004 earthquake.
The 2004 experience was unprecedented in South Asia. Unaffected by tsunami hazards in the past, tsunami geology is a nascent field for most South Asian researchers. Very little background field data is available on the deformational features of great earthquakes along this plate boundary and the depositional characteristics of extreme coastal surges, such as tsunamis and storms. Where do we begin our search for evidence of past tsunamigenic earthquakes? How best can we use the 2004 tsunami and its deposits as a proxy? What problems are encountered in the interpretations? This thesis addresses these questions in part and presents observations from the Andaman Islands (the ~400 km, northern segment of the Sumatra-Andaman subduction zone) and the southeast coast of India, towards developing a reliable database of tsunami geology for 2004-type events.
The premise is that regions affected by the 2004 earthquake are more likely to conserve signatures from older events. Based on the stratigraphic context of the proxy and quality of age estimates, this work presents evidence for past earthquake related deformation and tsunami deposition. In this work we use deformational and depositional features from the Andaman Islands, falling within the 2004 rupture zone and from one location on the Tamil Nadu coast of India (Kaveripattinam). From a perceptive understanding of the features related to tectonic deformation of the Sumatra-Andaman subduction zone, we have selected the Andaman segment that demonstrates explicit evidence for deformation and tsunami deposition through geomorphological and stratigraphic features, which are key to our exploration. A gist of each chapter is given below.
The introduction (chapter 1) presents the background, motivation and scope of this work and the organization of this thesis, also summarizing the contents of each chapter. Chapter 2 provides a review of literature on subduction zone earthquakes and updates on tsunami geology, to place this study in the global context. The next two chapters discuss the seismotectonics of the Sumatra-Andaman plate boundary, the important earthquakes and their source processes. In chapter 3 we discuss the Andaman segment (from 10–15° N), characterized by relatively lower level seismicity, but distinctive, as it falls within the northern limit of the 2004 rupture. The deformational and depositional features here are better exposed due to availability of land straddling the hinge line separating the areas of 2004 uplift and subsidence. Here, the pre-2004 earthquakes used to occur along a gently dipping subducting slab, up to a depth of about 40 km. Post-2004, the earthquakes moved up-dip, extending also to the outer-rise and outer-ridge regions, expressing post-earthquake relaxation [Andrade and Rajendran, 2011]. The southern Nicobar segment (5–10° N) differs from the Andaman segment in its style of deformation and seismic productivity. The decreasing obliquity of convergence, the likely influence of a subducting ocean ridge on the subducting plate and the character of the subducting oceanic plate make this segment distinctly different. In chapter 4 we present an analysis of its seismotectonic environment based on the well-constrained focal mechanisms of historic and recent earthquakes. We report that left-lateral strike-slip faulting on near N-S oriented faults control the deformation and the style of faulting is consistent to ~80 km within the subducting slab [Rajendran, K. et al., 2011]. The 11 April 2012 sequence of earthquakes on the subducting oceanic plate, between the Sumatra Trench and the Ninety East Ridge are the more recent among the oceanic intraplate earthquakes that demonstrate the reactivation of N-S oriented fossil fractures.
The limited availability of land and the 2004 coseismic deformation dominated by subsidence, followed by prolonged waterlogging makes exploration difficult in the Nicobar segment. Thus, we focus on the Andaman Islands for deformational and depositional evidence, using observations that can be corroborated through multiple proxies and depositional environments that are not prone to other coastal surges, such as cyclones and storms. The criteria for selection of sites, evaluation of deposits and determination of limiting ages are discussed in chapters 5 through 9. In chapter 5 we discuss different types of coastal environments and their response to high-energy sea surges. We also give a brief review of the comparative analyses of storm and tsunami deposits, a highly debated issue and then discuss important characteristics of these two deposits, using examples from the 2004 tsunami and the 2011 Thane cyclone that affected parts of the Tamil Nadu coast.
An important component of tsunami geology is the ability to identify and select datable material from tsunami deposits and chose an appropriate method for dating (chapter 6). The types of material used vary from peat layers, peat-rich soil, gastropod shells, wood, charcoal, organic remains such as bones, coral fragments, pottery sherds and buried soil. Techniques such as AMS Carbon-14 and Thermoluminescence are commonly used with appropriate calibrations and corrections. In addition to the dates generated in this study (based on wood and shell dates) we use some previous dates from the entire stretch of the rupture within the Indian Territory and assign a relative grading to these ages, based on the quality criterion evolved in this study. We believe that this is the first attempt to segregate age data obtained from coastal deposits, and assign them a specific quality grading based on their environment of deposition and the type of material dated.
Chapter 7 presents results of our investigations in the Andaman Islands, which cover ~30% of the rupture area. A coseismically subsided mangrove from Rangachanga (Port Blair, east coast of South Andaman) led us to a former subsidence during AD 770–1040, which we believe is the most convincing evidence for a previous tectonic event. Data based on inland deposits of coral and organic debris yielded a younger age in the range of AD 1480–1660. Both these dates fall in the age brackets reported from other regions of this plate boundary (mainly Sumatra) as well as distant shores of Sri Lanka, Thailand and mainland India. To understand the nature of distant deposits, we present observations from Kaveripattinam, an ancient port city on the east coast of India, where a high-energy sea surge deposit, found 1 km inland is attributed to a paleotsunami. The inland location of this archeological site at an elevation of 2 m and characteristics of the deposit that help discriminate it from typical storm deposition provide clinching evidence in favor of a 1000-year old regional tsunami (chapter 8).
In chapter 9 we discuss the results of our study. We evaluate the nature of deformation/deposition and the calibrated age data in the context of their environments. Ages based on the organic material associated with coral debris (at Hut Bay and Interview Island) and the remains of mangrove roots, 1 m below the present ground level (at Port Blair) are considered as reliable estimates, due to their sheltered inland location and the in situ root horizon used for dating. Age data from Kaveripattinam is also considered reliable, based on its inland location beyond the reach of storm surges, sediment characteristics typical of tsunami deposition and ages based on multiple methods and samples. The age data based on the sites presented in this thesis are more conclusive about the 800 to 1100 AD and 1250 to 1450 AD tsunamis, and the former is represented from regions closer to the 2004 source as well as distant shores reached by its tsunami.
Chapter 10 presents our conclusions and the scope for future studies. We present this as the first study of its kind in the northeastern Bay of Bengal, wherein the coseismic vertical coastal deformation features along an interplate subduction boundary and a variety of tsunami deposits are used to categorize depositional environments and ages of paleoearthquakes and tsunamis. To our knowledge, this is the first study of its kind where the effects of a recent tsunami have been used to evaluate paleodeposits based on their respective environments of occurrence. Our results have implications for tsunami geology studies in coastal regions prone to tsunami hazard
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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