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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Determination of the energy magnitude ME : application to rapid response purposes and insights to regional/local variabilities

Di Giacomo, Domenico January 2010 (has links)
Recent large earthquakes put in evidence the need of improving and developing robust and rapid procedures to properly calculate the magnitude of an earthquake in a short time after its occurrence. The most famous example is the 26 December 2004 Sumatra earthquake, when the limitations of the standard procedures adopted at that time by many agencies failed to provide accurate magnitude estimates of this exceptional event in time to launch early enough warnings and appropriate response. Being related to the radiated seismic energy ES, the energy magnitude ME is a good estimator of the high frequency content radiated by the source which goes into the seismic waves. However, a procedure to rapidly determine ME (that is to say, within 15 minutes after the earthquake occurrence) was required. Here it is presented a procedure able to provide in a rapid way the energy magnitude ME for shallow earthquakes by analyzing teleseismic P‑waves in the distance range 20-98. To account for the energy loss experienced by the seismic waves from the source to the receivers, spectral amplitude decay functions obtained from numerical simulations of Greens functions based on the average global model AK135Q are used. The proposed method has been tested using a large global dataset (~1000 earthquakes) and the obtained rapid ME estimations have been compared to other magnitude scales from different agencies. Special emphasis is given to the comparison with the moment magnitude MW, since the latter is very popular and extensively used in common seismological practice. However, it is shown that MW alone provide only limited information about the seismic source properties, and that disaster management organizations would benefit from a combined use of MW and ME in the prompt evaluation of an earthquake’s tsunami and shaking potential. In addition, since the proposed approach for ME is intended to work without knowledge of the fault plane geometry (often available only hours after an earthquake occurrence), the suitability of this method is discussed by grouping the analyzed earthquakes according to their type of mechanism (strike-slip, normal faulting, thrust faulting, etc.). No clear trend is found from the rapid ME estimates with the different fault plane solution groups. This is not the case for the ME routinely determined by the U.S. Geological Survey, which uses specific radiation pattern corrections. Further studies are needed to verify the effect of such corrections on ME estimates. Finally, exploiting the redundancy of the information provided by the analyzed dataset, the components of variance on the single station ME estimates are investigated. The largest component of variance is due to the intra-station (record-to-record) error, although the inter-station (station-to-station) error is not negligible and is of several magnitude units for some stations. Moreover, it is shown that the intra-station component of error is not random but depends on the travel path from a source area to a given station. Consequently, empirical corrections may be used to account for the heterogeneities of the real Earth not considered in the theoretical calculations of the spectral amplitude decay functions used to correct the recorded data for the propagation effects. / Starke Erdbeben in letzter Zeit zeigten deutlich den steigenden Bedarf nach einer Verbesserung und Entwicklung von stabilen und schnellen Methoden, um die Magnitude eines Erdbebens korrekt innerhalb kürzester Zeit nach dessen Auftreten zu ermitteln. Das bisher bekannteste Fallbeispiel in diesem Zusammenhang stellt das Sumatra-Erdbeben vom 26 Dezember 2004 dar. Dieses außergewöhnliche Ereignis zeigte deutlich die Grenzen der bisher gängigen und von den meisten Behörden zu dieser Zeit verwendeten Methoden zur Ermittlung der Erdbebenmagnitude. So konnte für dieses Beben mit den gängigen Ansätzen zeitnah die Magnitude nicht korrekt bestimmt werden / um eine angemessene Frühwarnung und entsprechende Gegenmaßnahmen einzuleiten. Die Energiemagnitude ME steht in direkter Verbindung mit der abgestrahlten seismischen Energie ES und stellt somit eine guten Abschätzung für den Hochfrequenzanteil dar, der von der Quelle ausgestrahlt wird und in die seismischen Wellen einfließt. Eine Methode, welche eine schnelle Ermittlung von ME ermöglicht (d.h. innerhalb von maximal 15 Minuten nach dem Erdbeben) wäre in diesem Falle benötigt worden. Im Rahmen dieser Arbeit wird eine Methode vorgestellt, die eine solche schnelle Ermittlung der Energiemagnitude ME für oberflächennahe Erdbeben ermöglicht, indem teleseismische P-Wellen im Bereich von 20°-98° analysiert werden. Um den Energieverlust der seismischen Wellen von deren Quelle bis zu den Empfängern angemessen zu berücksichtigen, werden spektrale Amplituden-Abnahmefunktionen verwendet, welche aus numerischen Simulationen von Greenschen Funktionen basierend auf dem durchschnittlichen globalen Modell AK135Q abgeleitet werden. Die vorgestellte Methode wurde mit einem umfangreichen globalen Datensatz (ca. 1000 Erdbeben) getestet, und die zeitnah ermittelten ME-Abschätzungen wurden mit anderen Magnitudenskalen verschiedener Behörden verglichen. Ein Vergleich mit der Momentenmagnitude MW war hierbei von besonderem Interesse, da diese Skala heutzutage weitverbreitet ist und häufig zum Einsatz kommt. Es zeigt sich jedoch, dass MW alleine nur begrenzte Informationen über die seismischen Herdeigenschaften liefern kann, und dass Organisationen des Katastrophenmagements von einer kombinierten Nutzung von MW und ME gerade hinsichtlich der unmittelbaren Evaluierung des tsunamigenen Potentials und der Erschütterungswirkung eines Erdbebens profitieren könnten. Die verwendete Methode zur Ermittlung von ME kommt ohne Wissen über die geometrischen Eigenschaften der Verwerfungszone aus (diese sind meist erst Stunden nach einem Erbeben verfügbar). Entsprechend wird die Eignung dieser Methode durch Eingruppierungen der analysierten Erdbeben nach ihrem Wirkungsmechanismus (Scherbruch, Abschiebung, Aufschiebung, etc.) diskutiert. Für die schnelle Abschätzung von ME ist kein klarer Trend unter Verwendung der verschiedenen Herdflächenlösungen erkennbar. Für ME-Werte, welche standardmäßig vom U.S. Geological Survey mit speziellen Korrekturwerten für die Abstrahlungscharakteristika ermittelt werden, trifft dies jedoch nicht zu. Weitere Untersuchungen sind nötig, um die Auswirkungen solcher Korrekturen auf die ME-Abschätzungen zu verifizieren. Indem die Redundanz der Informationen des analysierten Datensatzes ausgenutzt wurde, konnte die Varianz bei den Einzelstations-ME-Abschätzungen untersucht werden. Die größte Abweichung zeigt sich aufgrund von Intra-Stations-Fehlern (record-to-record), wenngleich auch der Inter-Stations-Fehler (station-to-station) nicht vernachlässigbar ist; so nimmt er für einige Stationen mehrere Magnitudeneinheiten an. Des Weiteren konnte gezeigt werden, dass der Intra-Stations-Anteil des Gesamtfehlers nicht zufällig ist, sondern abhängig vom Wellenweg von einem Quellgebiet zu einer bestimmten Station. Folglich können empirische Korrekturen dazu benutzt werden, den Heterogenitäten der realen Erde gerecht zu werden, welche heutzutage nicht in den theoretischen Kalkulationen der spektralen Amplituden-Abnahmefunktionen zur Korrektur der aufgezeichneten Daten verwendet werden.
2

Improving nuclear explosion detection using seismic and geomorphic data sets

Zeiler, Cleat Philip, January 2008 (has links)
Thesis (Ph. D.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.
3

The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling

Gregg, Patricia Michelle Marie January 2008 (has links)
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references. / Segmentation and crustal accretion at oceanic transform fault systems are investigated through a combination of geophysical data analysis and geodynamical and geochemical modeling. Chapter 1 examines the effect of fault segmentation on the maximum predicted earthquake magnitude of an oceanic transform fault system. Results of thermal modeling suggest that fault segmentation by intra- transform spreading centers (ITSC) drastically reduces the available brittle area of a transform fault and thus limits the available earthquake rupture area. Coulomb stress models suggest that long ITSCs will prohibit static stress interaction between segments of a transform system and further limit the maximum possible magnitude of a given transform fault earthquake. In Chapter 2, gravity anomalies from a global set of oceanic transform fault systems are investigated. Surprisingly, negative residual mantle Bouguer gravity anomalies are found within fast-slipping transform fault domains. These gravity observations suggest a mass deficit within fast-slipping transform faults, which may result from porosity variations, mantle serpentinization, and/or crustal thickness variations. Two-dimensional forward modeling and the correlation of the negative gravity anomalies to bathymetric highs indicate crustal thickness excesses in these locations. Finally, in Chapter 3, mantle thermal and melting models for a visco-plastic rheology are developed to investigate the process of mantle melting and crustal accretion at ITSCs within segmented transform faults, and are applied to the Siqueiros transform fault system. Models in which melt migrates into the transform fault domain from a large region of the mantle best explain the gravity-derived crustal thickness variations observed at the Siqueiros transform. Furthermore, a mantle potential temperature of 1350⁰C and fractional crystallization at depths of 9 - 15.5 km best explain the major element composition variation observed at the Siqueiros transform. / by Patricia Michelle Marie Gregg. / Ph.D.
4

Global investigations of radiated seismic energy and real-time implementation

Convers, Jaime Andres 13 January 2014 (has links)
This dissertation contains investigations of radiated seismic energy measurements from large earthquakes and duration determinations as significant properties of the dynamic earthquake rupture and its applications in the identification of very large and slow source rupturing earthquakes. This includes a description of earthquake released seismic energy from 1997 to 2010 and identification of slow source tsunami earthquakes in that time period. The implementation of these measurements in real-time since the beginning of 2009, with a case study of the Mentawai 2010 tsunami earthquake are also discussed. Further studies of rupture duration assessments and its technical improvements for more rapid and robust solutions are investigated as well, with application to the Tohoku-Oki 2011 earthquake an a case of directivity in the 2007 Mw 8.1 Solomon islands earthquake. Finally, the set of routines and programs developed for implementation at Georgia Tech and IRIS to produce the real-time results since 2009 presented in this study are described.
5

Main Seismological Features Of Recently Compiled Turkish Strong Motion Database

Erdogan, Ozgur 01 July 2008 (has links) (PDF)
In this thesis it is aimed to compile the Turkish strong-motion database for its efficient use in earthquake engineering and strong-motion seismology related studies. Within this context, the Turkish strong-motion database is homogenized in terms of basic earthquake source parameters (e.g. magnitude, style-of-faulting) as well as site classes and different source-to-site distance metrics. As part of this objective, empirical relationships for different magnitude scales are presented for further harmonization of the database. Data processing of the selected raw (unprocessed) strong-motion accelerograms that do not suffer from non-standard problems are realized. A comparative study is also conducted between the peak ground-motion values of Turkish strong-motion database with the estimations computed from different ground-motion prediction models. This way the regional differences of Turkish database are evaluated by making use of global prediction models. It is believed that the main products of this thesis will be of great use for reliable national seismic risk and hazard studies.

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