scholarly journals Understanding Seismic Waves Generated by Train Traffic via Modeling: Implications for Seismic Imaging and Monitoring

2020 ◽  
Vol 92 (1) ◽  
pp. 287-300
Author(s):  
François Lavoué ◽  
Olivier Coutant ◽  
Pierre Boué ◽  
Laura Pinzon-Rincon ◽  
Florent Brenguier ◽  
...  
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Seismic Imaging ◽  
Moving Load ◽  
Frequency Content ◽  
Important Conclusion ◽  
Near Surface ◽  
Radiated Energy ◽  
Train Speed ◽  
High Frequency Content

Abstract Trains are now recognized as powerful sources for seismic interferometry based on noise correlation, but the optimal use of these signals still requires a better understanding of their source mechanisms. Here, we present a simple approach for modeling train-generated signals inspired by early work in the engineering community, assuming that seismic waves are emitted by sleepers regularly spaced along the railway and excited by passing train wheels. Our modeling reproduces well seismological observations of tremor-like emergent signals and of their harmonic spectra. We illustrate how these spectra are modulated by wheel spacing, and how their high-frequency content is controlled by the distribution of axle loads over the rail, which mainly depends on ground stiffness beneath the railway. This is summarized as a simple rule of thumb that predicts the frequency bands in which most of train-radiated energy is expected, as a function of train speed and of axle distance within bogies. Furthermore, we identify two end-member mechanisms—single stationary source versus single moving load—that explain two types of documented observations, characterized by different spectral signatures related to train speed and either wagon length or sleeper spacing. In view of using train-generated signals for seismic applications, an important conclusion is that the frequency content of the signals is dominated by high-frequency harmonics and not by fundamental modes of vibrations. Consequently, most train traffic worldwide is expected to generate signals with a significant high-frequency content, in particular in the case of trains traveling at variable speeds that produce truly broadband signals. Proposing a framework for predicting train-generated seismic wavefields over meters to kilometers distance from railways, this work paves the way for high-resolution passive seismic imaging and monitoring at different scales with applications to near-surface surveys (aquifers, civil engineering), natural resources exploration, and natural hazard studies (landslides, earthquakes, and volcanoes).

Understanding seismic waves generated by train traffic via modelling

2020 ◽  
Author(s):  
François Lavoué ◽  
Olivier Coutant ◽  
Pierre Boué ◽  
Laura Pinzon-Rincon ◽  
Florent Brenguier ◽  
...  
Keyword(s):  
Fundamental Frequency ◽  
High Frequency ◽  
Doppler Effect ◽  
Seismic Waves ◽  
Moving Load ◽  
Harmonic Spectrum ◽  
Frequency Content ◽  
Rail Track ◽  
Train Speed ◽  
High Frequency Content

<p>Trains have recently been recognised as powerful sources for seismic imaging and monitoring based on the correlation of continuous noise records, but the optimal use of these signals still requires a better understanding of their source mechanisms. In this study, we present a simple approach for modelling train-generated seismic signals inspired from early work in the engineering community, which assumes that seismic waves are emitted by  sleepers regularly spaced along the railway and excited by the passage of the train wheels. <br>     As already known in the engineering literature, we exemplify the importance of the spatial distribution of each axle load over the rail track on the high-frequency content of the corresponding source time functions, and therefore of the final seismograms resulting from the contributions of all sleepers. In practice, this high-frequency content mainly depends on ground stiffness beneath the railway.<br>     Furthermore, we identify two end-member mechanisms to explain the two types of observations documented in the seismological literature. The first is the case of a single stationary source (fixed sleeper) excited by successive wheels of a train. This generates a harmonic spectrum characterised by a narrow spacing between frequency peaks related to a fundamental frequency <em>f<sub>1</sub> = V<sub>train</sub> / L<sub>w</sub></em> controlled by train speed and wagon length. The second is the case of a single moving load (single wheel) exciting all sleepers along the railway. This also yields a harmonic spectrum, but with a larger spacing between frequency peaks, related to a fundamental frequency <em>f<sub>2</sub> = V<sub>train</sub> / Δ<sub>sleeper</sub></em>  controlled by train speed and sleeper spacing. This moving source also generates a clear Doppler effect. <br>     In more realistic cases, considering all wheels and all sleepers, our modelling well reproduces the observations, both in the frequency domain (harmonic spectra) and in the time domain (tremor-like emergent shapes). The dominance of the previously-identified end-member mechanisms depends on sleeper regularity: perfectly-regular sleepers generate signals dominated by the signature of a single moving load with fundamental frequency <em>f<sub>2</sub></em> and a clear Doppler effect, while slightly-irregular sleepers generate signals dominated by the signature of stationary sources with fundamental frequency <em>f<sub>1</sub></em>. We speculate that our modelling parameter of sleeper regularity actually depends on the properties of the railway infrastructure in real cases.<br>     Finally, we discuss the perspectives of this work in view of using train-generated signals for seismic imaging and monitoring. In this regard, an important conclusion is that the frequency content of the signals is dominated by interferences between harmonic waves. Therefore, the exact value of the fundamental frequency at play matters less than the generation and preservation of the high frequencies, which depend on the distribution of the train load over the rail track and on propagation effects (medium heterogeneities, scattering and attenuation). Therefore, most of train traffic worldwide is expected to generate signals with a significant frequency content in the band [1 - 50] Hz of interest for seismic applications, in particular in the case of trains travelling at variable speeds which are expected to produce truly broadband signals. </p>

The application of reflection seismology to the investigation of the geometry of near-surface units and faults in the Blake River Group, Abitibi Belt, Quebec

1992 ◽  
Vol 29 (9) ◽  
pp. 2038-2045 ◽  
Author(s):  
Erick Adam ◽  
Bernd Milkereit ◽  
Marianne Mareschal ◽  
Arthur E. Barnes ◽  
Claude Hubert ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Reflection ◽  
Mineral Exploration ◽  
Shear Waves ◽  
Reflection Seismology ◽  
Frequency Content ◽  
Near Surface ◽  
Surface Geology ◽  
High Frequency Content

Reprocessing of part of a Lithoprobe high-resolution seismic reflection line across the southern part of the Abitibi Belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology. Enhancement of early reflections was accomplished by focusing on the high-frequency content of the data. This improved resolution of reflections at two-way traveltime as early as 0.3 s and attenuated noise such as shear waves. The shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase–diorite body and metavolcanics rocks. Offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block, which may be of interest for mineral exploration.

Comparison of wavelet continuous transform and signal averaged ECG for high frequency content and late potential detection in healthy individuals

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
D Garcia Iglesias ◽  
J.M Rubin Lopez ◽  
D Perez Diez ◽  
C Moris De La Tassa ◽  
F.J De Cos Juez ◽  
...  
Keyword(s):  
High Frequency ◽  
Classical Method ◽  
Total Power ◽  
Frequency Content ◽  
Healthy Individuals ◽  
Time Frequency ◽  
Qt Intervals ◽  
Long Time ◽  
Power Content ◽  
High Frequency Content

Abstract Introduction The Signal Averaged ECG (SAECG) is a classical method forSudden Cardiac Death (SCD) risk assessment, by means of Late Potentials (LP) in the filtered QRS (fQRS)[1]. But it is highly dependent on noise and require long time records, which make it tedious to use. Wavelet Continuous Transform (WCT) meanwhile is easier to use, and may let us to measure the High Frequency Content (HFC) of the QRS and QT intervals, which also correlates with the risk of SCD [2,3]. Whether the HFC of the QRS and QT measured with the WCT is a possible subrogate of LP, has never been demonstrated. Objective To demonstrate if there is any relationship between the HFC measured with the WCT and the LP analyzed with the SAECG. Methods Data from 50 consecutive healthy individuals. The standard ECG was digitally collected for 3 consecutive minutes. For the WCT Analysis 8 consecutive QT complexes were used and for the SAECG Analysis all available QRS were used. The time-frequency data of each QT complex were collected using the WCT as previously described [3] and the Total, QRS and QT power were obtained from each patient. For the SAECG, bipolar X, Y and Z leads were used with a bidirectional filter at 40 to 250 Hz [1]. LP were defined as less than 0.05 z in the terminal part of the filtered QRS and the duration (SAECG LP duration) and root mean square (SAECG LP Content) of this LP were calculated. Pearson's test was used to correlate the Power content with WCT analysis and the LP in the SAECG. Results There is a strong correlation between Total Power and the SAECG LP content (r=0.621, p<0.001). Both ST Power (r=0.567, p<0.001) and QRS Power (r=0.404, p=0.004) are related with the SAECG LP content. No correlation were found between the Power content (Total, QRS or ST Power) and the SAECG LP duration. Also no correlation was found between de SAECG LP content and duration. Conclusions Total, QRS and ST Power measured with the WCT are good surrogates of SAECG LP content. No correlation were found between WCT analysis and the SAECG LP duration. Also no correlation was found between the SAECG LP content and duration. This can be of high interest, since WCT is an easier technique, not needing long recordings and being less affected by noise. Funding Acknowledgement Type of funding source: None

Broadband seismic over/under sources and their designature-deghosting

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. P61-P73 ◽  
Author(s):  
Lasse Amundsen ◽  
Ørjan Pedersen ◽  
Are Osen ◽  
Johan O. A. Robertsson ◽  
Martin Landrø
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Low Frequency ◽  
Point Sources ◽  
High Frequency Side ◽  
Frequency Content ◽  
Source Depth ◽  
Deep Sources ◽  
The Cost ◽  
High Frequency Content

The source depth influences the frequency band of seismic data. Due to the source ghost effect, it is advantageous to deploy sources deep to enhance the low-frequency content of seismic data. But, for a given source volume, the bubble period decreases with the source depth, thereby degrading the low-frequency content. At the same time, deep sources reduce the seismic bandwidth. Deploying sources at shallower depths has the opposite effects. A shallow source provides improved high-frequency content at the cost of degraded low-frequency content due to the ghosting effect, whereas the bubble period increases with a lesser source depth, thereby slightly improving the low-frequency content. A solution to the challenge of extending the bandwidth on the low- and high-frequency side is to deploy over/under sources, in which sources are towed at two depths. We have developed a mathematical ghost model for over/under point sources fired in sequential and simultaneous modes, and we have found an inverse model, which on common receiver gathers can jointly perform designature and deghosting of the over/under source measurements. We relate the model for simultaneous mode shooting to recent work on general multidepth level array sources, with previous known solutions. Two numerical examples related to over/under sequential shooting develop the main principles and the viability of the method.

scholarly journals HIGH FREQUENCY CONTENT OF THE SURFACE ECG CORRELATES WITH THE PRESENCE OF SYMPATHETIC NERVES IN THE VENTRICLES OF THE HEART

2017 ◽  
Vol 69 (11) ◽  
pp. 422
Author(s):  
Larisa G. Tereshchenko ◽  
Golriz Sedaghat ◽  
Ryan Gardner ◽  
Muammar Kabir ◽  
Beth Habecker
Keyword(s):  
High Frequency ◽  
Sympathetic Nerves ◽  
Frequency Content ◽  
Surface Ecg ◽  
High Frequency Content

scholarly journals Standing shock prevents propagation of sparks in supersonic explosive flows

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Jens von der Linden ◽  
Clare Kimblin ◽  
Ian McKenna ◽  
Skyler Bagley ◽  
Hsiao-Chi Li ◽  
...  
Keyword(s):  
Radio Frequency ◽  
High Frequency ◽  
Fluid Dynamic ◽  
Supersonic Jet ◽  
Explosive Eruptions ◽  
Jet Flows ◽  
Frequency Content ◽  
Frequency Regime ◽  
High Frequency Content ◽  
Volcanic Jet

AbstractVolcanic jet flows in explosive eruptions emit radio frequency signatures, indicative of their fluid dynamic and electrostatic conditions. The emissions originate from sparks supported by an electric field built up by the ejected charged volcanic particles. When shock-defined, low-pressure regions confine the sparks, the signatures may be limited to high-frequency content corresponding to the early components of the avalanche-streamer-leader hierarchy. Here, we image sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Fluid dynamic and kinetic simulations of the experiment demonstrate that the observed sparks originate upstream of the standing shock. The sparks are initiated in the rarefaction region, and cut off at the shock, which would limit their radio frequency emissions to a tell-tale high-frequency regime. We show that sparks transmit an impression of the explosive flow, and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena.

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