1,720,962 research outputs found
A multibranch, multitarget neural network for rapid point-source inversion in a microseismic environment: examples from the Hengill Geothermal Field, Iceland
Full text linkDespite advanced seismological techniques, automatic source characterization for microseismic earthquakes remains difficult and challenging since current inversion and modelling of high-frequency signals are complex and time consuming. For real-time applications such as induced seismicity monitoring, the application of standard methods is often not fast enough for true complete real-time information on seismic sources. In this paper, we present an alternative approach based on recent advances in deep learning for rapid source-parameter estimation of microseismic earthquakes. The seismic inversion is represented in compact form by two convolutional neural networks, with individual feature extraction, and a fully connected neural network, for feature aggregation, to simultaneously obtain full moment tensor and spatial location of microseismic sources. Specifically, a multibranch neural network algorithm is trained to encapsulate the information about the relationship between seismic waveforms and underlying point-source mechanisms and locations. The learning-based model allows rapid inversion (within a fraction of second) once input data are available. A key advantage of the algorithm is that it can be trained using synthetic seismic data only, so it is directly applicable to scenarios where there are insufficient real data for training. Moreover, we find that the method is robust with respect to perturbations such as observational noise and data incompleteness (missing stations). We apply the new approach on synthesized and example recorded small magnitude (M ≤ 1.6) earthquakes at the Hellisheiði geothermal field in the Hengill area, Iceland. For the examined events, the model achieves excellent performance and shows very good agreement with the inverted solutions determined through standard methodology. In this study, we seek to demonstrate that this approach is viable for microseismicity real-time estimation of source parameters and can be integrated into advanced decision-support tools for controlling induced seismicity
Verbesserung von Standard-Verfahren zur Abschätzung von seismischen Quellparametern auf regionalen und teleseismischen Distanzen
No full textSeismological agencies play an important role in seismological research and seismic hazard mitigation by providing source parameters of seismic events (location, magnitude, mechanism), and keeping these data accessible in the long term. The availability of catalogues of seismic source parameters is an important requirement for the evaluation and mitigation of seismic hazards, and the catalogues are particularly valuable to the research community as they provide fundamental long-term data in the geophysical sciences. This work is well motivated by the rising demand for developing more robust and efficient methods for routine source parameter estimation, and ultimately generation of reliable catalogues of seismic source parameters. Specifically, the aim of this work is to develop some methods to determine hypocentre location and temporal evolution of seismic sources based on regional and teleseismic observations more accurately, and investigate the potential of these methods to be integrated in near real-time processing.
To achieve this, a location method that considers several events simultaneously and improves the relative location accuracy among nearby events has been provided. This method tries to reduce the biasing effects of the lateral velocity heterogeneities (or equivalently to compensate for limitations and inaccuracies in the assumed velocity model) by calculating a set of timing corrections for each seismic station. The systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure can be corrected without explicitly solving for a velocity model. Application to sets of multiple earthquakes in complex tectonic environments with strongly heterogeneous structure such as subduction zones and plate boundary region demonstrate that this relocation process significantly improves the hypocentre locations compared to standard locations.
To meet the computational demands of this location process, a new open-source software package has been developed that allows for efficient relocation of large-scale multiple seismic events using arrival time data. Upon that, a flexible location framework is provided which can be tailored to various application cases on local, regional, and global scales. The latest version of the software distribution including source codes, a user guide, an example data set, and a change history, is freely available to the community.
The developed relocation algorithm has been modified slightly and then its performance in a simulated near real-time processing has been evaluated. It has been demonstrated that applying the proposed technique significantly reduces the bias in routine locations and enhance the ability to locate the lower magnitude events using only regional arrival data.
Finally, to return to emphasis on global seismic monitoring, an inversion framework has been developed to determine the seismic source time function through direct waveform fitting of teleseismic recordings. The inversion technique can be systematically applied to moderate- size seismic events and has the potential to be performed in near real-time applications. It is exemplified by application to an abnormal seismic event; the 2017 North Korean nuclear explosion.
The presented work and application case studies in this dissertation represent the first step in an effort to establish a framework for automatic, routine generation of reliable catalogues of seismic event locations and source time functions.Seismologische Dienste spielen eine wichtige Rolle in der seismologischen Forschung und Gefährdungsanalyse, indem sie Quellparameter für seismische Ereignisse (Lokalisierung, Stärke, Mechanismus) bereitstellen und diese Daten langfristig verfügbar machen. Die Verfügbarkeit von Katalogen seismischer Quellparameter ist eine wichtige Voraussetzung für die Bewertung der seismischen Gefährdung und Minderung der Auswirkungen von Erdbeben. Die seismischen Kataloge sind für die Forschungsgemeinschaft besonders wertvoll, da sie grundlegende Hintergrundsdaten über lange Zeiträume liefern. Die vorliegende Arbeit ist motiviert durch die steigende Nachfrage nach der Entwicklung robusterer und effizienterer Methoden für die routinemäßige Schätzung von Quellparametern und schließlich die Verbesserung der Qualität und Quantität der seismischen Kataloge. Ziel dieser Arbeit ist es insbesondere Methoden zu entwickeln, um die Lokalisierung von Hypozentren und die zeitliche Entwicklung der Momentfreisetzung bei einem Erdbeben auf der Grundlage regionaler und teleseismischer Beobachtungen genauer zu bestimmen, und das Potenzial dieser Methoden für eine zeitnahe Verarbeitung zu untersuchen.
Um dies zu erreichen, wurde eine Lokalisierungsmethode bereitgestellt, die mehrere Ereignisse gleichzeitig berücksichtigt und die relative Genauigkeit der Hypozentren zwischen benachbarten Ereignissen verbessert. Dieses Verfahren versucht, die Verzerrungen durch Geschwindigkeits-heterogenitäten zu reduzieren, oder äquivalent Einschränkungen und Ungenauigkeiten in dem angenommenen Geschwindigkeitsmodell auszugleichen, indem richtungsabhängige Zeitkorrekturen für jede seismische Station berechnet werden. Die systematischen Fehler, die durch die Ungenauigkeiten in der angenommenen Geschwindigkeitsstruktur in die Lokalisierung projiziert werden, können korrigiert werden, ohne explizit nach einem Geschwindigkeitsmodell zu lösen. Die Anwendung auf Ensemble von Erdbeben in tektonischen Situationen mit stark heterogener, komplexer Struktur wie Subduktionszonen und Plattengrenzregionen zeigt, dass diese Relokalisierung die Hypozentren im Vergleich zu Standardlokalisierungen signifikant verbessert.
Um den rechnerischen Anforderungen der Lokalisierung gerecht zu werden, wurde ein neues Open-Source-Softwarepaket entwickelt, das eine effiziente Relokalisierung einer großen Anzahl von Erdbeben unter Verwendung von Ankunftszeitdaten ermöglicht. Daraufhin wird ein flexibler Lokalisierungsrahmen bereitgestellt, der an verschiedene Fälle auf lokaler, regionaler und globaler Ebene angepasst werden kann. Die neueste Version der Software einschließlich Quellcodes, Benutzerhandbuch, Beispieldatensatz und Änderungsverlauf ist für die Öffentlichkeit frei verfügbar.
Der entwickelte Relokalisierungs-Algorithmus wurde geringfügig verändert und anschließend seine Leistung in einem simulierten Echtzeit Prozess bewertet. Es zeigte sich, dass die Anwendung der vorgeschlagenen Technik die Verzerrung der Hypozentren der Routineauswertung erheblich verringert und die Fähigkeit zum Lokalisieren der Ereignisse mit niedriger Magnitude unter Verwendung nur regionaler Ankunftsdaten verbessert.
Um sich wieder auf die globale seismische Überwachung zu konzentrieren, wurde schließlich ein Inversionssystem entwickelt, um die Zeitfunktion der seismischen Quelle durch direkte Wellenformanpassung von teleseismischen Aufzeichnungen zu bestimmen. Die Inversionstechnik kann systematisch auf seismische Ereignisse mittlerer Größe angewendet werden und hat das Potenzial, in nahezu Echtzeitanwendungen ausgeführt zu werden. Dies wird beispielhaft durch die Anwendung auf ein abnormales seismisches Ereignis veranschaulicht: die nordkoreanische Atomexplosion 2017.
Die in dieser Dissertation vorgestellten Arbeits- und Anwendungsfallstudien stellen den ersten Schritt dar, um einen Rahmen für die automatische, routinemäßige Erzeugung zuverlässiger Kataloge von seismischen Ereignisorten und Quellzeitfunktion zu schaffen
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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