scholarly journals Observation and explanation of spurious seismic signals emerging in teleseismic noise correlations

2019 ◽  
Author(s):  
Lei Li ◽  
Pierre Boué ◽  
Michel Campillo
Keyword(s):  
Stationary Phase ◽  
Seismic Noise ◽  
Body Waves ◽  
Seismic Signals ◽  
Noise Sources ◽  
Correlation Operator ◽  
Common Path ◽  
Spatially Distributed ◽  
Ray Path ◽  
Spurious Signals

Abstract. Deep body waves have been reconstructed from seismic noise correlations in recent studies. Authors prospect their great potentials in deep-Earth imaging. In addition to the expected physical seismic phases, some spurious arrivals having no correspondence in earthquake seismograms are observed from the noise correlations. The origins of the noise-derived body waves have not been well understood. Traditionally, the reconstruction of seismic phases from inter-receiver noise correlations is attributed to the interference between waves from noise sources in the stationary-phase regions. The interfering waves emanating from a stationary-phase location have a common ray path from the source to the first receiver. The correlation operator cancels the common path and extracts a signal corresponding to the inter-receiver ray path. In this study, with seismic noise records from two networks at teleseismic distance, we show that noise-derived spurious seismic signals without correspondence in real seismograms can arise from the interference between waves without common ray path or common slowness. These noise-derived signals cannot be explained by the traditional stationary-phase arguments. Numerical experiments reproduce the observed spurious signals. These signals still emerge for uniformly distributed noise sources, and thus are not caused by localized sources. We interpret the presence of the spurious signals with a less restrictive condition of quasi-stationary phase: providing the time delays between interfering waves from spatially distributed noise sources are close enough, the stack of correlation functions over the distributed sources can still be constructive as an effect of finite frequencies, and thereby noise-derived signals emerge from the source averaging.

scholarly journals Observation and explanation of spurious seismic signals emerging in teleseismic noise correlations

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 173-184 ◽  
Author(s):  
Lei Li ◽  
Pierre Boué ◽  
Michel Campillo
Keyword(s):  
Stationary Phase ◽  
Seismic Noise ◽  
Body Waves ◽  
Seismic Signals ◽  
Noise Sources ◽  
Correlation Operator ◽  
Common Path ◽  
Spatially Distributed ◽  
Ray Path ◽  
Spurious Signals

Abstract. Deep body waves have been reconstructed from seismic noise correlations in recent studies. The authors note their great potential for deep-Earth imaging. In addition to the expected physical seismic phases, some spurious arrivals having no correspondence in earthquake seismograms are observed from the noise correlations. The origins of the noise-derived body waves have not been well understood. Traditionally, the reconstruction of seismic phases from inter-receiver noise correlations is attributed to the interference between waves from noise sources in the stationary-phase regions. The interfering waves emanating from a stationary-phase location have a common ray path from the source to the first receiver. The correlation operator cancels the common path and extracts a signal corresponding to the inter-receiver ray path. In this study, with seismic noise records from two networks at teleseismic distance, we show that noise-derived spurious seismic signals without correspondence in real seismograms can arise from the interference between waves without a common ray path or common slowness. These noise-derived signals cannot be explained by traditional stationary-phase arguments. Numerical experiments reproduce the observed spurious signals. These signals still emerge for uniformly distributed noise sources, and thus are not caused by localized sources. We interpret the presence of the spurious signals with a less restrictive condition of quasi-stationary phase: providing the time delays between interfering waves from spatially distributed noise sources are close enough, the stack of correlation functions over the distributed sources can still be constructive as an effect of finite frequencies, and thereby noise-derived signals emerge from the source averaging.

On the Feasibility of Long-term Seismic Monitoring Using Freight Train Signals

2021 ◽  
Author(s):  
Yixiao Sheng ◽  
Florent Brenguier ◽  
Pierre Boué ◽  
Aurélien Mordret ◽  
Yehuda Ben-Zion ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Body Wave ◽  
Time Windows ◽  
Seismic Monitoring ◽  
Body Waves ◽  
Time Shift ◽  
Seismic Signals ◽  
Noise Sources ◽  
Seismic Arrays

<div>Recent studies (Brenguier et al., 2019; Pinzon-Rincon et al., 2020) have successfully retrieved body waves between seismic arrays through the correlations of train-generated seismic signals. It remains uncertain whether these train-derived body waves are suitable for long-term seismic monitoring, which requires repeatable measurements over the years. This study tests the feasibility of obtaining stable body waves between individual broadband stations, using freight trains as noise sources. We use stations close to the railroad as markers to identify trains and pinpoint their potential locations. We select proper station pairs and perform seismic interferometry, focusing on the time windows when trains are detected. We test our workflow in southern California, with the freight trains running through the Coachella Valley. We successfully retrieve stable body-wave signals over ten years. We perform a weekly stacking to improve the signal-to-noise ratio and estimate the relative time shift. Our preliminary time-shift measurements reveal a systematic long-term increasing trend for station pairs locating on two sides of the San Jacinto fault. The next step is to examine the results statistically to reduce the bias introduced by moving sources. Despite that the long-term trend still needs further study, our experiment demonstrates that it is possible to perform long-term seismic monitoring using train generated seismic signals.</div>

scholarly journals Improvements in seismic resolution and current limitations in the Global Seismographic Network

2019 ◽  
Vol 220 (1) ◽  
pp. 508-521 ◽  
Author(s):  
A T Ringler ◽  
J Steim ◽  
D C Wilson ◽  
R Widmer-Schnidrig ◽  
R E Anthony
Keyword(s):  
Seismic Noise ◽  
Broad Band ◽  
Earth Tide ◽  
Seismic Signals ◽  
Noise Levels ◽  
Noise Sources ◽  
Long Period ◽  
Seismic Resolution ◽  
Fundamental Limitation ◽  
Seismographic Network

SUMMARY Station noise levels play a fundamental limitation in our ability to detect seismic signals. These noise levels are frequency-dependent and arise from a number of physically different drivers. At periods greater than 100 s, station noise levels are often limited by the self-noise of the instrument as well as the sensitivity of the instrument to non-seismic noise sources. Recently, station operators in the Global Seismographic Network (GSN) have deployed several Streckeisen STS-6A very broad-band borehole seismometers. These sensors provide a potential replacement for the no-longer-produced Streckeisen STS-1 seismometer and the GeoTech KS-54 000 borehole seismometer. Along with showing some of the initial observational improvements from installing modern very broad-band seismometers at depth, we look at current limitations in the seismic resolution from earth tide periods 100 000 s (0.01 mHz) to Nyquist at most GSN sites (0.02 s or 50 Hz). Finally, we show the potential for improved observations of continuously excited horizontal Earth hum as well as the splitting of very long-period torsional modes. Both of these observations make use of the low horizontal noise levels which are obtained by installing very broad-band borehole seismometers at depth.

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

scholarly journals Imaging New Zealand's Crustal Structure Using Ambient Seismic Noise Recordings from Permanent and Temporary Instruments

2021 ◽  
Author(s):  
◽  
Yannik Behr
Keyword(s):  
Seismic Noise ◽  
Cross Correlation ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Ambient Seismic Noise ◽  
Uppermost Mantle ◽  
Noise Sources ◽  
Noise Field ◽  
Rayleigh And Love Waves ◽  
Noise Cross Correlation

<p>We use ambient seismic noise to image the crust and uppermost mantle, and to determine the spatiotemporal characteristics of the noise field itself, and examine the way in which those characteristics may influence imaging results. Surface wave information extracted from ambient seismic noise using cross-correlation methods significantly enhances our knowledge of the crustal and uppermost mantle shear-velocity structure of New Zealand. We assemble a large dataset of three-component broadband continuous seismic data from temporary and permanent seismic stations, increasing the achievable resolution of surface wave velocity maps in comparison to a previous study. Three-component data enables us to examine both Rayleigh and Love waves using noise cross-correlation functions. Employing a Monte Carlo inversion method, we invert Rayleigh and Love wave phase and group velocity dispersion curves separately for spatially averaged isotropic shear velocity models beneath the Northland Peninsula. The results yield first-order radial anisotropy estimates of 2% in the upper crust and up to 15% in the lower crust, and estimates of Moho depth and uppermost mantle velocity compatible with previous studies. We also construct a high-resolution, pseudo-3D image of the shear-velocity distribution in the crust and uppermost mantle beneath the central North Island using Rayleigh and Love waves. We document, for the first time, the lateral extent of low shear-velocity zones in the upper and mid-crust beneath the highly active Taupo Volcanic Zone, which have been reported previously based on spatially confined 1D shear-velocity profiles. Attributing these low shear-velocities to the presence of partial melt, we use an empirical relation to estimate an average percentage of partial melt of < 4:2% in the upper and middle crust. Analysis of the ambient seismic noise field in the North Island using plane wave beamforming and slant stacking indicates that higher mode Rayleigh waves can be detected, in addition to the fundamental mode. The azimuthal distributions of seismic noise sources inferred from beamforming are compatible with high near-coastal ocean wave heights in the period band of the secondary microseism (~7 s). Averaged over 130 days, the distribution of seismic noise sources is azimuthally homogeneous, indicating that the seismic noise field is well-suited to noise cross-correlation studies. This is underpinned by the good agreement of our results with those from previous studies. The effective homogeneity of the seismic noise field and the large dataset of noise cross-correlation functions we here compiled, provide the cornerstone for future studies of ambient seismic noise and crustal shear velocity structure in New Zealand.</p>

Statistical properties of Rayleigh waves due to scattering by topography

1967 ◽  
Vol 57 (1) ◽  
pp. 83-90
Author(s):  
J. A. Hudson ◽  
L. Knopoff
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Forward Scattering ◽  
Statistical Properties ◽  
Body Waves ◽  
Simplified Model ◽  
Two Dimensional ◽  
Especial Reference ◽  
The Earth

abstract The two-dimensional problems of the scattering of harmonic body waves and Rayleigh waves by topographic irregularities in the surface of a simplified model of the earth are considered with especial reference to the processes of P-R, SV-R and R-R scattering. The topography is assumed to have certain statistical properties; the scattered surface waves also have describable statistical properties. The results obtained show that the maximum scattered seismic noise is in the range of wavelengths of the order of the lateral dimensions of the topography. The process SV-R is maximized over a broader band of wavelengths than the process P-R and thus the former may be more difficult to remove by selective filtering. An investigation of the process R-R shows that backscattering is much more important than forward scattering and hence topography beyond the array must be taken into account.

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.

Rayleigh group velocity extraction from ambient seismic noise to map the south Eastern Cape Karoo region, South Africa

2017 ◽  
Vol 120 (3) ◽  
pp. 341-350 ◽  
Author(s):  
L.J. Bezuidenhout ◽  
M. Doucouré ◽  
V. Wagener ◽  
M. de Wit ◽  
A. Mordret ◽  
...  
Keyword(s):  
South Africa ◽  
Surface Waves ◽  
Group Velocity ◽  
Seismic Noise ◽  
Vertical Component ◽  
Ambient Seismic Noise ◽  
Seismic Signals ◽  
The South ◽  
Velocity Anomaly ◽  
Rayleigh Surface Waves

Abstract The Karoo region of South Africa is an ideal laboratory to use ambient seismic signals to map the shallow subsurface, as it is a quiet and pristine environment with a geology that is relatively well known. Ambient seismic signals were continuously recorded for a ten week period between August and October 2015. The ambient seismic noise network consisted of two groups of 17 temporary, stand-alone seismic stations each. These were installed in the southeastern Cape Karoo region, near the town of Jansenville. Here we present data on the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. We reconstruct and show, for the first time in the southeastern Cape Karoo, estimates of Green's function from cross-correlating ambient noise data between stations pairs, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 3 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. The resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth, which shows a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly could correspond to the overlying Jurassic-Cretaceous sedimentary sequences of the younger Algoa Basin (Uitenhage Group).

A linear algorithm for ambient seismic noise double beamforming without explicit crosscorrelations

Geophysics ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. F1-F8
Author(s):  
Eileen R. Martin
Keyword(s):  
Correlation Functions ◽  
Seismic Noise ◽  
Ambient Noise ◽  
Computational Cost ◽  
Body Waves ◽  
Ambient Seismic Noise ◽  
Noise Correlation ◽  
Dense Array ◽  
Near Surface ◽  
Noise Interferometry

Geoscientists and engineers are increasingly using denser arrays for continuous seismic monitoring, and they often turn to ambient seismic noise interferometry for low-cost near-surface imaging. Although ambient noise interferometry greatly reduces acquisition costs, the computational cost of pair-wise comparisons between all sensors can be prohibitively slow or expensive for applications in engineering and environmental geophysics. Double beamforming of noise correlation functions is a powerful technique to extract body waves from ambient noise, but it is typically performed via pair-wise comparisons between all sensors in two dense array patches (scaling as the product of the number of sensors in one patch with the number of sensors in the other patch). By rearranging the operations involved in the double beamforming transform, I have developed a new algorithm that scales as the sum of the number of sensors in two array patches. Compared to traditional double beamforming of noise correlation functions, the new method is more scalable, easily parallelized, and it does not require raw data to be exchanged between dense array patches.

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