scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
Vol 2(11)2011 (2(11)) ◽  
pp. 344-346
Author(s):  
V.P. Shljahovyj ◽  
◽  
O. Kendzera ◽  
V.V. Shljahovyj ◽  
◽  
...  
Keyword(s):  
Seismic Waves ◽  
Seismic Signal ◽  
Long Period ◽  
Gravitational Contribution

Possibility of use of tidal devices for record of seismic waves from earthquakes and other geodynamic events is studied. It is investigated the inertial and gravitational contribution of seismic signal to pendular seismometers and tidal devices (seismotiltmeter and gravimeter). These are identical devices and differ stability of blocks and in filtration parameters. Tidal devices are more sensitive in over-long-period area where the gravitational contribution is more. It is given examples of record of seismic fluctuations by tidal devices at some earthquakes

Isolation Performance of Intelligent Seismic Isolation System Using Air Bearing

2009 ◽  
Author(s):  
Satoshi Fujita ◽  
Keisuke Minagawa ◽  
Mitsuru Miyazaki ◽  
Go Tanaka ◽  
Toshio Omi ◽  
...  
Keyword(s):  
Seismic Isolation ◽  
Seismic Waves ◽  
Three Dimensional ◽  
Vertical Motion ◽  
Air Bearings ◽  
Natural Period ◽  
Isolation System ◽  
Vertical Excitation ◽  
Long Period ◽  
Isolation Performance

This paper describes three-dimensional isolation performance of seismic isolation system using air bearings. Long period seismic waves having predominant period of from a few seconds to a few ten seconds have recently been observed in various earthquakes. Also resonances of high-rise buildings and sloshing of petroleum tanks in consequence of long period seismic waves have been reported. Therefore the isolation systems having very long natural period or no natural period are required. In a previous paper [1], we proposed an isolation system having no natural period by using air bearings. Additionally we have already reported an introduction of the system, and have investigated horizontal motion during earthquake in the previous paper. It was confirmed by horizontal vibration experiment and simulation in the previous paper that the proposed system had good performance of isolation. However vertical motion should be investigated, because vertical motion varies horizontal frictional force. Therefore this paper describes investigation regarding vertical motion of the proposed system by experiment. At first, a vertical excitation test of the system is carried out so as to investigate vertical dynamic property. Then a three-dimensional vibration test using seismic waves is carried out so as to investigate performance of isolation against three-dimensional seismic waves.

Very-Long-Period (VLP) Seismic Artifacts during the 2018 Caldera Collapse at Kīlauea, Hawai‘i

2020 ◽  
Vol 91 (6) ◽  
pp. 3417-3432
Author(s):  
Ashton F. Flinders ◽  
Ingrid A. Johanson ◽  
Phillip B. Dawson ◽  
Kyle R. Anderson ◽  
Matthew M. Haney ◽  
...  
Keyword(s):  
Amplitude Spectrum ◽  
Low Frequency ◽  
Seismic Signal ◽  
Sinc Function ◽  
Caldera Collapse ◽  
Velocity Amplitude ◽  
Long Period ◽  
Ramp Function ◽  
Instrument Response ◽  
Summit Caldera

Abstract Throughout the 2018 eruption of Kīlauea volcano (Hawai‘i), episodic collapses of a portion of the volcano’s summit caldera produced repeated Mw 4.9–5.3 earthquakes. Each of these 62 events was characterized by a very-long-period (VLP) seismic signal (>40  s). Although collapses in the later stage of the eruption produced earthquakes with significant amplitude clipping on near-summit broadband seismometers, the first 12 were accurately recorded. For these initial collapse events, we compare average VLP seismograms at six near-summit locations to synthetic seismograms derived from displacements at collocated Global Positioning System stations. We show that the VLP seismic signal was generated by a radially outward and upward ramp function in displacement. We propose that at local distances the period of the VLP seismic signal is solely dependent on the duration of this ramp function and the instrument transfer function, that is, the seismic VLP is an artifact of the bandlimited instrument response and not representative of real ground motion. The displacement ramp function imposes a sinc-function velocity amplitude spectrum that cannot be fully recovered through standard seismic instrument deconvolution. Any near-summit VLP signals in instrument-response-corrected velocity or displacement seismograms from these collapse events are subject to severe band limitation. Similarly, the seismic amplitude response is not flat through the low-frequency corner, for example, instrument-response-uncorrected seismograms scaled by instrument sensitivity are equally prone to band limitation. This observation is crucial when attempting to clarify the different contributions to the VLP source signature. Not accounting for this effect could lead to misunderstanding of the magmatic processes involved.

scholarly journals Seismic monitoring of torrential and fluvial processes

2016 ◽  
Vol 4 (2) ◽  
pp. 285-307 ◽  
Author(s):  
Arnaud Burtin ◽  
Niels Hovius ◽  
Jens M. Turowski
Keyword(s):  
Seismic Noise ◽  
Seismic Waves ◽  
Seismic Signal ◽  
Seismic Monitoring ◽  
Surface Processes ◽  
Seismic Signals ◽  
Seismic Arrays ◽  
Time Frequency ◽  
Continuous Survey ◽  
Long Time

Abstract. In seismology, the signal is usually analysed for earthquake data, but earthquakes represent less than 1 % of continuous recording. The remaining data are considered as seismic noise and were for a long time ignored. Over the past decades, the analysis of seismic noise has constantly increased in popularity, and this has led to the development of new approaches and applications in geophysics. The study of continuous seismic records is now open to other disciplines, like geomorphology. The motion of mass at the Earth's surface generates seismic waves that are recorded by nearby seismometers and can be used to monitor mass transfer throughout the landscape. Surface processes vary in nature, mechanism, magnitude, space and time, and this variability can be observed in the seismic signals. This contribution gives an overview of the development and current opportunities for the seismic monitoring of geomorphic processes. We first describe the common principles of seismic signal monitoring and introduce time–frequency analysis for the purpose of identification and differentiation of surface processes. Second, we present techniques to detect, locate and quantify geomorphic events. Third, we review the diverse layout of seismic arrays and highlight their advantages and limitations for specific processes, like slope or channel activity. Finally, we illustrate all these characteristics with the analysis of seismic data acquired in a small debris-flow catchment where geomorphic events show interactions and feedbacks. Further developments must aim to fully understand the richness of the continuous seismic signals, to better quantify the geomorphic activity and to improve the performance of warning systems. Seismic monitoring may ultimately allow the continuous survey of erosion and transfer of sediments in the landscape on the scales of external forcing.

Fundamental Study on the Super-Long-Period Active Isolation System

2004 ◽  
Author(s):  
Keisuke Minagawa ◽  
Satoshi Fujita
Keyword(s):  
Control System ◽  
Seismic Isolation ◽  
Seismic Waves ◽  
Model Matching ◽  
Fundamental Study ◽  
Natural Period ◽  
Isolation System ◽  
Long Period ◽  
Rubber Bearings ◽  
Classical Control

Since the Hanshin-Awaji Earthquake Disaster, the number of isolated structures has been greatly increased. The natural period of the isolation system is designed around 3 seconds, because predominate period of observed seismic waves is usually 0.1 to 1 second. However, relatively long period seismic waves have been observed in various earthquakes, and the resonance of long-period structures, such as high-rise buildings, during earthquakes have been reported at the same time. Therefore the natural period needs to be extended. When extending the natural period of the isolated structure using rubber bearings, its stiffness needs to be reduced. It is more difficult to extend the natural period of the isolation system than the conventional system because of its buckling problem. Therefore we propose a super-long-period active seismic isolation system as a new method for extending the natural period of the isolated structure. This system consists of rubber bearings and actuators. In this study, we designed a control system by using the model-matching-method. This is one of the classical control system design methods. We investigated the isolation performance by numerical analysis. In addition, we selected the optimal variables of transfer function using genetic algorithm.

Analysis of seismic wave dynamics by means of integral representations and the method of discontinuities

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 413-418 ◽  
Author(s):  
Anton A. Duchkov ◽  
Sergey V. Goldin
Keyword(s):  
Seismic Wave ◽  
Seismic Waves ◽  
Seismic Signal ◽  
Integral Representations ◽  
Synthetic Signal ◽  
Point Of Interest ◽  
Series Approximation ◽  
The Time Domain ◽  
Phase Distortions ◽  
Ray Series

We analyze the dynamics (amplitudes and phase distortions) of seismic waves as they propagate along the ray. Our analysis is performed via a ray series approximation in the time domain. That is, we concentrate on characterizing the sharp changes (discontinuities) of the signal that are localized near the wavefront. After convolution of the terms of such a series with a proper temporally short (high‐frequency) wavelet, one obtains a synthetic seismic signal at a given point of interest. We present an outline of the proposed technique that yields integrals describing the wavefield. These integrals are similar to oscillatory integrals in the frequency domain. This description is uniformly valid near caustics, allowing the calculation of higher order terms of the ray series approximation. Practical use of the technique is illustrated by several examples which show two possible uses of the technique: general understanding of what is happening during wave propagation and practical calculations. First, we show how the structure of the ray decomposition changes near the simple caustic, and then we calculate a synthetic signal near the cusp caustic. The advantage of the technique is that the problem of seismic wave calculation is technically reduced to a problem of double integration of a Dirac δ-function; thus, it is computationally effective.

scholarly journals METHODS OF SEISMIC DATA PROCESSING FOR SOLVING TASKS OF MONITORING OF FOREIGN TESTING LANDS

2021 ◽  
pp. 31-41
Author(s):  
Y. O. Gordienko ◽  
A. O. Lotoshko ◽  
O. O. Paplinskiy
Keyword(s):  
Data Processing ◽  
Seismic Waves ◽  
Dynamic Properties ◽  
International System ◽  
Reference Signal ◽  
Measurement Data ◽  
Correlation Method ◽  
Seismic Signal ◽  
Seismic Monitoring ◽  
Seismic Stations

The paper analyzes the methods of processing measurement data of the seismic observation method used in the International Seismic Monitoring System and the Main Center for Special Control of the State Space Agency of Ukraine to solve problems of monitoring nuclear tests at foreign test sites. The directions of improvement of known and development of new methods of processing of measuring data of seismic method of detection in the conditions of presence and absence of a priori information on the form of a seismic signal are defined. If the form of the expected seismic signal is known, then the monitoring of foreign test sites by the seismic grouping system can be realized by supplementing the method of controlled directional reception with a correlation scheme of measurement data processing. In the absence of information on the shape of the seismic signal, the monitoring of the test site is carried out by dividing the group into two subgroups, followed by the cross-correlation method between the original samples of each subgroup. For a network of three-component stations, if there is information about the shape of the expected seismic signal, the method of comparison with the reference signal is used. In the absence of reference signals, monitoring is implemented using system discriminant, which takes into account the kinetic and dynamic properties of the expected signal with a cell from a given area. Possibilities of application of seismic stations of the International system of seismic monitoring are analyzed, use of measuring data which for the decision of problems of monitoring of foreign landfills allows to reduce time of definition of parameters of a seismic event essentially. A feature of the signals registered by seismic stations of the International System is the presence of types of seismic waves characteristic of events with cells in the near zone. Implementation of monitoring of test sites is possible by taking into account the polarization and dynamic properties of seismic waves. The implementation of the proposed approaches will increase the efficiency of solving the problem of detecting nuclear explosions at foreign test sites.

Detecting local and regional seismic events using the data-adaptive method at the VAF seismograph station in Finland

1991 ◽  
Vol 81 (4) ◽  
pp. 1373-1379
Author(s):  
Matti Tarvainen
Keyword(s):  
Detection Threshold ◽  
Seismic Signal ◽  
Adaptive Method ◽  
Digital Data ◽  
Seismic Events ◽  
Visual Methods ◽  
Long Period ◽  
Detection Window ◽  
Seismograph Station ◽  
Data Adaptive

Abstract The data-adaptive autoregressive (hereafter DA) method was used to detect local and regional seismic events using digital data from the Vaasa (VAF) station with co-ordinates (62.3°N, 22.2°E) in western Finland. The seismic signal and the noise were assumed to have been normally distributed stochastic processes with a zero mean. The parameters of these processes were then adapted on the change of the registered signal as a function of time within a predefined detection window. The accuracy of the method presented is compared with the STA/LTA and visual methods. When the same detection threshold was used with the DA detector and the STA/LTA detector, it was found that the DA detector was more precise in detecting the onsets of seismic events. Bandpass (1.5 to 20 Hz) filtering was used in all the events discussed. This was done to reject the long-period microseismic noise. In one case, the detector was used on nonfiltered as well as filtered data, in order to show coinciding results.

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