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  • 1
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    Basel, Boston, Berlin : Birkhäuser
    Keywords: seismology ; earthquake
    Description / Table of Contents: Earthquake rupture is a process of remarkable complexity. Over the past few decades, scientists have become aware of its high variability on all scales as well as its wide dynamic range. At the same time, a thorough understanding of the seismic source process is a key element of reliable earthquake ground motion prediction. The present book contains a comprehensive collection of contributions originating from the 2012 ECGS Workshop Earthquake Source Physics on Various Scales, held in Luxembourg. The seventeen articles in this volume cover theoretical and observational aspects of the earthquake source process, ranging from tiny, laboratory-generated M -6 events to the source complexity and radiated energy of the world’s greatest earthquakes. Among other aspects, the papers provide new insights into the relationship of earthquake recurrence time with fault frictional parameters, how the results of lab-based friction experiments relate to observational source studies, and how geometrical source complexity can be quantified. In particular, several papers are devoted to the question whether small and large earthquakes scale self-similarly or if they show differences in their dynamic source characteristics, which is one of the most hotly debated aspects of modern seismology. The volume provides an integrated view of the current state-of-the-art knowledge on the earthquake source process on all scales and will be useful to students and professional researchers who are interested in these phenomena.
    Pages: Online-Ressource (VI, 330 Seiten)
    ISBN: 9783034808675
    Language: English
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  • 2
    Publication Date: 2017-06-10
    Description: For successful assessment and mitigation of earthquake hazards, it is necessary to be able to reliably predict the level of ground shaking which has to be expected from future large earthquakes. This prediction of ground motion can be done either by using empirical relations (derived from past earthquakes) between some ground motion parameter and the source and observer location, so-called attenuation relations, or by performing numerical simulations of future earthquakes based on models of the earthquake source and the propagation medium (i.e. the Earth). The capacity of the first option is at times rather limited, for instance if only very few large earthquakes occurred in the region of interest in instrumental times. Numerical simulations, on the other hand, cannot provide reliable results without a detailed description of the underlying source process and a thorough understanding of path and site effects. This thesis aims at a better understanding of the source process and the spectral characteristics of the intermediate-depth Vrancea (Romania) earthquakes...
    Description: thesis
    Keywords: TSE 000 ; TOH 400
    Language: English
    Type: monograph , publishedVersion
    Format: 205 S.
    Format: application/pdf
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  • 3
    Publication Date: 2016-10-24
    Description: Abstract
    Description: KivuSNet represents the first dense broadband seismic network installed in the Kivu Rift region, which is located in the bordering region of the Democratic Republic of Congo and Rwanda. Here the active volcanoes Nyamulagira (the most active in Africa) and Nyiragongo (host to the largest persistent lava lake on Earth) threaten the city of Goma and neighbouring agglomerations, and destructive earthquakes can also affect the region. The deployement started with the first stations in 2012/2013 and since October 2015, 13 stations are operated with real-time data transmission. The development of KivuSNet has been carried out in the framework of several research projects and is in particular associated with the project REmote Sensing and In Situ detection and Tracking of geohazards (RESIST), funded by the Belgian Science Policy and the National Research Fund of Luxembourg. KivuSNet aims at opening a new window for the seismological knowledge in this highly active rifting region, allowing for unprecedented insights into tectonic and volcanic seismicity, tremor patterns and Earth structure as well as for sustainable real-time monitoring of the volcanoes in the area. Together with the often co-located KivuGNet geodetic stations, KivuSNet closes a dramatic observational gap in this region. Waveform data is available from the GEOFON data centre, under network code KV, and is embargoed.
    Keywords: Seismic monitoring ; Monitoring system ; Seismological stations
    Type: Other , Seismic Network
    Format: Approximately 17 active stations
    Format: SEED data
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  • 4
    Publication Date: 2013-01-01
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2009-02-01
    Description: Seismograms from 55 intermediate-depth Vrancea earthquakes (M 4.0-7.1) recorded at 43 stations of an accelerometric network in Romania are used to derive source spectra and site amplification functions from S waves in the frequency range 0.5-20 Hz with the generalized inversion technique (GIT) (Castro et al., 1990). Attenuation is taken into account using the nonparametric attenuation functions derived by Oth et al. (2008) from the same dataset, and the attenuation-corrected data are then split into source and site contributions. The source spectra follow the omega (super -2) model (Brune, 1970, 1971) with high corner frequencies and a related Brune stress drop of the order of 100 MPa. The site amplification functions are separately determined for both horizontal and vertical components. Contrary to widespread expectation, the vertical component shows significant amplification effects at high frequencies. The H/Z ratios determined from the GIT results compare well with H/V ratios computed directly from the S-wave window of the accelerograms (Lermo and Chavez-Garcia, 1993). The basic assumption for the determination of site effects from H/V ratios is that the vertical component is not or only little affected by site effects. For Vrancea earthquakes, this assumption is incorrect; consequently, site effects should not be estimated from H/V ratios. The reason for this peculiar fact is the geometry of intermediate-depth seismicity that leads to almost vertical ray paths beneath the stations.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 6
    Publication Date: 2011-03-22
    Description: In this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the K-NET and KiK-net networks in Japan in order to derive attenuation characteristics, source spectra, and site response. For this purpose, we use a total of more than 67,000 S-wave records from 2178 earthquakes (M (sub JMA) 2.7-8) obtained at 1555 stations at the Earth's surface and more than 29,000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m. Attenuation characteristics are investigated in five separate regions, showing that crustal Q depicts lower values in central compared to southern Japan, and a significant frequency dependence is observed in every region. The source spectra follow the omega (super 2) model with higher stress drops for subcrustal earthquakes as compared with crustal ones. While strong amplification effects dominate the site contributions for the surface sensors, those for the borehole sensors are characterized by smaller variability. Nevertheless, consistent with observations from deconvolution of borehole/surface recording pairs, downgoing wave effects are visible in the site contributions for many borehole stations. Finally, the site amplification functions obtained at the surface are compared with surface-to-borehole (S/B) and horizontal-to-vertical (H/V) spectral ratios, showing that the S/B ratios generally provide better estimates of the horizontal amplification than the H/V ratios due to amplification of the vertical component of ground motion.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 7
    Publication Date: 2011-03-22
    Description: The wealth of accelerometric recordings collected by the K-NET and KiK-net networks in Japan since 1996 provides a unique opportunity to improve our understanding of many important seismological research questions. Subsets of these data have been used for many case studies, most of them, however, not focusing specifically on the best practices for data selection and giving relatively little attention to the properties and peculiarities directly observable from the data. Yet for many applications, these steps are an important prerequisite for successful and reliable analysis. For this reason, we devote this article to the extraction of a large data set of surface and borehole recordings from the K-NET and KiK-net databases with strong emphasis on data quality and reliability. The final data set available for subsequent work consists of 78,840 records from 2201 earthquakes covering the Japan Meteorological Agency (JMA) magnitude range 2.7-8, observed at 1681 sites throughout Japan. We explain how this data set has been compiled, including automatic phase picking and relocation of events. We also present an overview of the general features of the data set, providing important information for subsequent analysis. Strong amplification effects at high frequencies are immediately visible on the surface recordings. Furthermore, there is a clear presence of downgoing waves in the borehole records, as deconvolution of borehole/surface recording pairs indicates.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 8
    Publication Date: 2008-10-01
    Description: The S-wave attenuation characteristics beneath the Vrancea region in Romania are analyzed from the spectra (frequency range 0.5-20 Hz) of more than 850 recordings at 43 accelerometric stations of 55 intermediate-depth earthquakes (M 4.0-7.1) that occurred in the Vrancea seismogenic zone. The method commonly chosen for this type of investigation in the case of crustal earthquakes is the generalized inversion technique (GIT) (e.g., Andrews, 1986; Castro et al., 1990). Yet the Vrancea dataset is entirely different from common crustal datasets. Because of the strong clustering of the hypocenters within a very small focal volume, there are only few crossing ray paths from sources to receivers. As a consequence, inhomogeneities in the attenuation properties are not averaged out, which leads to unphysical results if the standard GIT approach is adopted. The problem is discussed qualitatively by performing tests with synthetic data and solved quantitatively by adapting the GIT technique in view of these peculiarities. With the optimally adapted inversion scheme, it is possible to unravel differences in the attenuation characteristics between two (or more) sets of stations. The results show that the attenuation of seismic waves is roughly comparable in the low frequency range (〈4-5 Hz) but stronger by up to an order of magnitude at higher frequencies within the Carpathian mountain arc as compared with the foreland area. Modeling this strongly frequency-dependent lateral variation of seismic attenuation by a significantly lower Q beneath Vrancea (1) provides a very good fit of observed strong-motion characteristics, (2) sheds new light on the distribution of intensities of the previous strong earthquakes, (3) will have strong implications for future hazard assessment, and (4) is fully compatible with structural models from deep seismic sounding, tomography, and teleseismic attenuation.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 9
    Publication Date: 2015-08-25
    Description: Expansion of urban areas in Central Asia increases their exposure to seismic hazard, but at present no earthquake early warning (EEW) systems exist in the region. Such systems, successfully implemented in other regions, aim to provide warning of the order of tens of seconds about impending disasters, enabling the first rapid‐response steps to be taken. The feasibility of such systems for Bishkek, Kyrgyzstan, has been demonstrated. This study investigates how the use of the spectral content, instead of just ground‐motion thresholds, can be used to improve the performance of proposed regional warning systems. We find that using the spectral content of the first few seconds after the P‐wave arrival can provide timely warning for events closer to the target city than was possible with the threshold systems. It is further shown that for events less than 60 km from the target, any regional system needs to be complemented with an onsite one to provide a comprehensive EEW system.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 10
    Publication Date: 2011-04-01
    Description: In this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the K-NET and KiK-net networks in Japan in order to derive attenuation characteristics, source spectra, and site response. For this purpose, we use a total of more than 67,000 S-wave records from 2178 earthquakes (MJMA 2.7-8) obtained at 1555 stations at the Earth's surface and more than 29,000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m. Attenuation characteristics are investigated in five separate regions, showing that crustal Q depicts lower values in central compared to southern Japan, and a significant frequency dependence is observed in every region. The source spectra follow the{omega} 2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones. While strong amplification effects dominate the site contributions for the surface sensors, those for the borehole sensors are characterized by smaller variability. Nevertheless, consistent with observations from deconvolution of borehole/surface recording pairs, downgoing wave effects are visible in the site contributions for many borehole stations. Finally, the site amplification functions obtained at the surface are compared with surface-to-borehole (S/B) and horizontal-to-vertical (H/V) spectral ratios, showing that the S/B ratios generally provide better estimates of the horizontal amplification than the H/V ratios due to amplification of the vertical component of ground motion.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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