The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Michele Barbato - One of the best experts on this subject based on the ideXlab platform.
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influence of time varying Frequency Content in earthquake ground motions on seismic response of linear elastic systems
Earthquake Engineering & Structural Dynamics, 2016Co-Authors: Joel P Conte, Michele BarbatoAbstract:Summary Earthquake ground motion records are nonstationary in both amplitude and Frequency Content. However, the latter nonstationarity is typically neglected mainly for the sake of mathematical simplicity. To study the stochastic effects of the time-varying Frequency Content of earthquake ground motions on the seismic response of structural systems, a pair of closely related stochastic ground motion models is adopted here. The first model (referred to as ground motion model I) corresponds to a fully nonstationary stochastic earthquake ground motion model previously developed by the authors. The second model (referred to as ground motion model II) is nonstationary in amplitude only and is derived from the first model. Ground motion models I and II have the same mean-square function and global Frequency Content but different features of time variation in the Frequency Content, in that no time variation of the Frequency Content exists in ground motion model II. New explicit closed-form solutions are derived for the response of linear elastic SDOF and MDOF systems subjected to stochastic ground motion model II. New analytical solutions for the evolutionary cross-correlation and cross-PSD functions between the ground motion input and the structural response are also derived for linear systems subjected to ground motion model I. Comparative analytical results are presented to quantify the effects of the time-varying Frequency Content of earthquake ground motions on the structural response of linear elastic systems. It is found that the time-varying Frequency Content in the seismic input can have significant effects on the stochastic properties of system response. Copyright © 2016 John Wiley & Sons, Ltd.
Farzin Zareian - One of the best experts on this subject based on the ideXlab platform.
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validation of simulated earthquake ground motions based on evolution of intensity and Frequency Content
Bulletin of the Seismological Society of America, 2015Co-Authors: Sanaz Rezaeian, Peng Zhong, Stephen H Hartzell, Farzin ZareianAbstract:Abstract Simulated earthquake ground motions can be used in many recent engineering applications that require time series as input excitations. However, applicability and validation of simulations are subjects of debate in the seismological and engineering communities. We propose a validation methodology at the waveform level and directly based on characteristics that are expected to influence most structural and geotechnical response parameters. In particular, three time-dependent validation metrics are used to evaluate the evolving intensity, Frequency, and bandwidth of a waveform. These validation metrics capture nonstationarities in intensity and Frequency Content of waveforms, making them ideal to address nonlinear response of structural systems. A two-component error vector is proposed to quantify the average and shape differences between these validation metrics for a simulated and recorded ground-motion pair. Because these metrics are directly related to the waveform characteristics, they provide easily interpretable feedback to seismologists for modifying their ground-motion simulation models. To further simplify the use and interpretation of these metrics for engineers, it is shown how six scalar key parameters, including duration, intensity, and predominant Frequency, can be extracted from the validation metrics. The proposed validation methodology is a step forward in paving the road for utilization of simulated ground motions in engineering practice and is demonstrated using examples of recorded and simulated ground motions from the 1994 Northridge, California, earthquake.
Emma Suriñach - One of the best experts on this subject based on the ideXlab platform.
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Infrasound produced by debris flow: propagation and Frequency Content evolution
Natural Hazards, 2014Co-Authors: Arnold Kogelnig, Johannes Hübl, Emma Suriñach, Ignasi Vilajosana, Brian W. McardellAbstract:Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-Frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-Frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.
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Frequency Content evolution of snow avalanche seismic signals
Surveys in Geophysics, 2003Co-Authors: Berta Biescas, Francois Dufour, Gloria Furdada, Giorgi Khazaradze, Emma SuriñachAbstract:Seismic signals generated by avalanches have been recorded by theavalanche team of the Universitat de Barcelona at theVallee de la Sionne experimental site (Switzerland) since 1998. During these years avalanches of varying size and flowwere recorded by two sensors located at different positions.In the present paper we show the general features of the running spectra of the seismicsignals for the different type of recorded avalanches. Using this method we are able not only to detect avalanches with low amplitude signals but also to distinguishbetween avalanches and other seismic sources (i.e., local earthquakes) which have thesame Frequency Content but a different Frequency evolution.
Stephen H Hartzell - One of the best experts on this subject based on the ideXlab platform.
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validation of simulated earthquake ground motions based on evolution of intensity and Frequency Content
Bulletin of the Seismological Society of America, 2015Co-Authors: Sanaz Rezaeian, Peng Zhong, Stephen H Hartzell, Farzin ZareianAbstract:Abstract Simulated earthquake ground motions can be used in many recent engineering applications that require time series as input excitations. However, applicability and validation of simulations are subjects of debate in the seismological and engineering communities. We propose a validation methodology at the waveform level and directly based on characteristics that are expected to influence most structural and geotechnical response parameters. In particular, three time-dependent validation metrics are used to evaluate the evolving intensity, Frequency, and bandwidth of a waveform. These validation metrics capture nonstationarities in intensity and Frequency Content of waveforms, making them ideal to address nonlinear response of structural systems. A two-component error vector is proposed to quantify the average and shape differences between these validation metrics for a simulated and recorded ground-motion pair. Because these metrics are directly related to the waveform characteristics, they provide easily interpretable feedback to seismologists for modifying their ground-motion simulation models. To further simplify the use and interpretation of these metrics for engineers, it is shown how six scalar key parameters, including duration, intensity, and predominant Frequency, can be extracted from the validation metrics. The proposed validation methodology is a step forward in paving the road for utilization of simulated ground motions in engineering practice and is demonstrated using examples of recorded and simulated ground motions from the 1994 Northridge, California, earthquake.
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signatures of the seismic source in emd based characterization of the 1994 northridge california earthquake recordings
Bulletin of the Seismological Society of America, 2003Co-Authors: Ray Ruichong Zhang, Stephen H HartzellAbstract:In this article we use empirical mode decomposition (EMD) to charac- terize the 1994 Northridge, California, earthquake records and investigate the sig- natures carried over from the source rupture process. Comparison of the current study results with existing source inverse solutions that use traditional data processing suggests that the EMD-based characterization contains information that sheds light on aspects of the earthquake rupture process. We first summarize the fundamentals of the EMD and illustrate its features through the analysis of a hypothetical and a real record. Typically, the Northridge strong-motion records are decomposed into eight or nine intrinsic mode functions (IMF's), each of which emphasizes a different oscillation mode with different amplitude and Frequency Content. The first IMF has the highest-Frequency Content; Frequency Content decreases with an increase in IMF component. With the aid of a finite-fault inversion method, we then examine aspects of the source of the 1994 Northridge earthquake that are reflected in the second to fifth IMF components. This study shows that the second IMF is predominantly wave motion generated near the hypocenter, with high-Frequency Content that might be related to a large stress drop associated with the initiation of the earthquake. As one progresses from the second to the fifth IMF component, there is a general migration of the source region away from the hypocenter with associated longer-period signals as the rupture propagates. This study suggests that the different IMF components carry information on the earthquake rupture process that is expressed in their different Frequency bands.
P.s.r. Diniz - One of the best experts on this subject based on the ideXlab platform.
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On the time-Frequency Content of Weyl-Heisenberg frames generated from odd and even functions [signal representation applications]
2005 IEEE International Symposium on Circuits and Systems, 2005Co-Authors: L. Lovisolo, M.g. De Pinho, E.a.b. Da Silva, P.s.r. DinizAbstract:This work discusses the time-Frequency Content of frames, especially of Weyl-Heisenberg frames. We begin by showing that the sum of the time-Frequency Contents of all the functions in a set being always positive is a sufficient condition for this set of functions to generate a frame. It is then derived that for Weyl-Heisenberg frames {E/sub mb/T/sub na/g(t)}/sub n,m//spl epsiv/z of an even function g(t) the maxima are placed at (na, mb) in the time-Frequency domain and the minima at (na+a/2, mb+b/2); whereas for an odd function g(t) the maxima are placed at (na, mb+b/2) and the minima at (na+a/2, mb). This indicates effective ways to, for a given increase in the cardinality of the frame, obtain "tighter" frame bounds.
