scholarly journals Investigating the seismic structure and visibility of dynamic plume models with seismic array methods

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S167-S194
Author(s):  
Fabienne Stockmann ◽  
Laura Cobden ◽  
Frédéric Deschamps ◽  
Andreas Fichtner ◽  
Christine Thomas
Keyword(s):  
Seismic Waves ◽  
Data Sets ◽  
Mantle Plumes ◽  
Seismic Structure ◽  
Optimum Frequency ◽  
Seismic Scattering ◽  
Out Of Plane ◽  
Waveform Modelling ◽  
D Region ◽  
Incoming Energy

SUMMARY Mantle plumes may play a major role in the transport of heat and mass through the Earth, but establishing their existence and structure using seismology has proven challenging and controversial. Previous studies have mainly focused on imaging plumes using waveform modelling and inversion (i.e. tomography). In this study we investigate the potential visibility of mantle plumes using array methods, and in particular whether we can detect seismic scattering from the plumes. By combining geodynamic modelling with mineral physics data we compute ‘seismic’ plumes whose shape and structure correspond to dynamically plausible thermochemical plumes. We use these seismic models to perform a full-waveform simulation, sending seismic waves through the plumes, in order to generate synthetic seismograms. Using velocity spectral analysis and slowness-backazimuth plots, we are unable to detect scattering. However at longer dominant periods (25 s) we see several arrivals from outside the plane of the great circle path, that are consistent with an apparent bending of the wave front around the plume conduit. At shorter periods (15 s), these arrivals are less obvious and less strong, consistent with the expected changes in the waves' behaviour at higher frequencies. We also detect reflections off the iron-rich chemical pile which serves as the plume source in the D″ region, indicating that D″ reflections may not always be due to a phase transformation. We suggest that slowness-backazimuth analysis may be a useful tool to locate mantle plumes in real array data sets. However, it is important to analyse the data at different dominant periods since, depending on the width of the plume, there is probably an optimum frequency band at which the plume is most visible. Our results also show the importance of studying the incoming energy in all directions, so that any apparently out-of-plane arrivals can be correctly interpreted.

Probing mantle plumes using seismic arrays

2020 ◽  
Author(s):  
Laura Cobden ◽  
Michael Afanasiev ◽  
Frederic Deschamps ◽  
Fabienne Stockmann ◽  
Christine Thomas ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Seismic Energy ◽  
Spectral Element ◽  
Mantle Plumes ◽  
Low Frequencies ◽  
Seismic Arrays ◽  
Seismic Waveforms ◽  
Waveform Modelling ◽  
And Inversion

<p>Elucidating the role of deep mantle plumes in mantle convection is challenging because their influence on seismic waveforms – which could be used to map their location – is subtle. Previous seismic studies have mainly focused on waveform modelling and inversion (i.e. tomography). In this study we instead consider the potential visibility of mantle plumes using array methods. We investigate, in particular, how plumes deviate seismic energy from the great-circle path. This requires a multidisciplinary approach: first, we perform geodynamic modelling to generate thermochemical plumes, and convert them to “seismic” plumes via thermodynamic modelling of mineral physics data. Next, spectral element methods are used to model the interaction of seismic waves with the plumes and generate synthetic seismograms. These seismograms are divided into arrays and we generate slowness-backazimuth plots for each array. With recent advances in computational methods and resources, we investigate wave behaviour at previously unattainable frequencies.  We find that plumes do indeed cause seismic waves to change direction, although the exact behaviour may be frequency-dependent, and at low frequencies we observe waves apparently bending around the plume conduit.  We consider how and where these results may be applied to real seismic arrays, to provide new constraints on the location and structure of mantle plumes.</p>

scholarly journals Seismic structure of the southern Apennines as revealed by waveform modelling of regional surface waves

2009 ◽  
Vol 178 (3) ◽  
pp. 1473-1492 ◽  
Author(s):  
Ahmet Ökeler ◽  
Yu Jeffrey Gu ◽  
Arthur Lerner-Lam ◽  
Michael S. Steckler
Keyword(s):  
Surface Waves ◽  
Seismic Structure ◽  
Southern Apennines ◽  
Waveform Modelling

An investigation into the fundamental relationships between attenuation, phase dispersion, and frequency using seismic refraction profiles over sedimentary structures

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 72-87 ◽  
Author(s):  
R. S. Jacobson
Keyword(s):  
Frequency Dependence ◽  
Seismic Waves ◽  
Velocity Dispersion ◽  
Seismic Refraction ◽  
Systematic Investigation ◽  
Data Sets ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
Apparent Attenuation ◽  
Seismic Refraction Data

Despite many attenuation measurements which indicate a linear functional frequency dependence of absorption or constant [Formula: see text] in sediments, several theories predict no such linear dependence. The primary justification for rejecting a first‐power frequency dependence of attenuation is that it implies that seismic waves cannot propagate causally. Seismic waves must also travel with some velocity dispersion to satisfy causality, yet there is a lack of velocity dispersion measurements in sediments. In‐situ attenuation is caused by two distinct mechanisms: anelastic heating, and scattering due to interbed multiples. Apparent, or scattering, attenuation can produce both frequency‐dependent and non‐frequency‐dependent effects. Accurate measurements of attenuation and velocity dispersion are difficult; it is not surprising that a systematic investigation into the frequency dependence of absorption and velocity has not been made. A reinvestigation into two seismic refraction data sets collected over thickly stratified deep‐sea fans indicates that [Formula: see text] should not be assumed to be independent of frequency. Further, significant frequency‐independent absorption is present, indicating a high degree of apparent attenuation. Phase, or velocity, dispersion was also measured, but the results are more ambiguous than those for attenuation, due to inherent limitations of digital signals. Nevertheless, the absorption and velocity dispersion results are largely compatible, suggesting that if apparent attenuation is observed, then the scattered waves propagate causally.

scholarly journals On the Lense-Thirring test with the Mars Global Surveyor in the gravitational field of Mars

Open Physics ◽  
2010 ◽  
Vol 8 (3) ◽  
Author(s):  
Lorenzo Iorio
Keyword(s):  
Gravitational Field ◽  
Data Sets ◽  
Mars Global Surveyor ◽  
Confidence Bounds ◽  
Data Set ◽  
Frame Dragging ◽  
Plane Component ◽  
Out Of Plane ◽  
Systematic Effects ◽  
Linear Fit

AbstractI discuss some aspects of a recent frame-dragging test performed by exploiting the Root-Mean-Square (RMS) orbit-overlap differences of the out-of-plane component (N) of the Mars Global Surveyor (MGS) spacecraft’s orbit in the gravitational field of Mars. A linear fit to the complete time series for the entire MGS data set (4 February 1999–14 January 2005) yields a normalized slope 1.03 ± 0.41 (with 95% confidence bounds). Other linear fits to different data sets confirm agreement with general relativity. Huge systematic effects induced by mismodeling the martian gravitational field which have been claimed by some authors are absent in the MGS out-of-plane record. The same level of effect is seen for both the classical non-gravitational and relativistic gravitomagnetic forces on the in-plane MGS orbital components; this is not the case for the out-of-plane components. Moreover, the non-conservative forces experience high-frequency variations which are not important in the present case where secular effects are relevant.

Least-squares Gaussian beam migration in viscoacoustic media

Geophysics ◽  
2020 ◽  
Vol 86 (1) ◽  
pp. S17-S28
Author(s):  
Yubo Yue ◽  
Yujin Liu ◽  
Yaonan Li ◽  
Yunyan Shi
Keyword(s):  
Green’S Function ◽  
Least Squares ◽  
Gaussian Beam ◽  
Green's Function ◽  
Seismic Waves ◽  
Image Resolution ◽  
Data Sets ◽  
Phase Dispersion ◽  
Using Data ◽  
Gaussian Beam Migration

Because of amplitude decay and phase dispersion of seismic waves, conventional migrations are insufficient to produce satisfactory images using data observed in highly attenuative geologic environments. We have developed a least-squares Gaussian beam migration method for viscoacoustic data imaging, which can not only compensate for amplitude decay and phase dispersion caused by attenuation, but it can also improve image resolution and amplitude fidelity through linearized least-squares inversion. We represent the viscoacoustic Green’s function by a summation of Gaussian beams, in which an attenuation traveltime is incorporated to simulate or compensate for attenuation effects. Based on the beam representation of the Green’s function, we construct the viscoacoustic Born forward modeling and adjoint migration operators, which can be effectively evaluated by a time-domain approach based on a filter-bank technique. With the constructed operators, we formulate a least-squares migration scheme to iteratively solve for the optimal image. Numerical tests on synthetic and field data sets demonstrate that our method can effectively compensate for the attenuation effects and produce images with higher resolution and more balanced amplitudes than images from acoustic least-squares Gaussian beam migration.

US Artifacts: Effects on Out-of-Plane US Images Reconstructed from Three-dimensional Data Sets

Radiology ◽  
2001 ◽  
Vol 218 (2) ◽  
pp. 592-597 ◽  
Author(s):  
Janet E. Bailey ◽  
Ronald O. Bude ◽  
Theresa Tuthill
Keyword(s):  
Three Dimensional ◽  
Data Sets ◽  
Out Of Plane

scholarly journals Multiresolution analysis and learning for computational seismic interpretation

2018 ◽  
Vol 37 (6) ◽  
pp. 443-450 ◽  
Author(s):  
Motaz Alfarraj ◽  
Yazeed Alaudah ◽  
Zhiling Long ◽  
Ghassan AlRegib
Keyword(s):  
Multiresolution Analysis ◽  
Seismic Data ◽  
Curvelet Transform ◽  
Discrete Wavelet ◽  
Data Sets ◽  
Seismic Structure ◽  
Subsurface Structures ◽  
Gaussian Pyramid ◽  
Seismic Image ◽  
Texture Attributes

We explore the use of multiresolution analysis techniques as texture attributes for seismic image characterization, especially in representing subsurface structures in large migrated seismic data. Namely, we explore the Gaussian pyramid, the discrete wavelet transform, Gabor filters, and the curvelet transform. These techniques are examined in a seismic structure labeling case study on the Netherlands offshore F3 block. In seismic structure labeling, a seismic volume is automatically segmented and classified according to the underlying subsurface structure using texture attributes. Our results show that multiresolution attributes improve the labeling performance compared to using seismic amplitude alone. Moreover, directional multiresolution attributes, such as the curvelet transform, are more effective than the nondirectional attributes in distinguishing different subsurface structures in large seismic data sets and can greatly help the interpretation process.

Analysis for the 3-Dimensional Time History Response of a Base-Isolated Building Structure

2011 ◽  
Vol 368-373 ◽  
pp. 1961-1964
Author(s):  
Jin Xia Kang
Keyword(s):  
Composite Structures ◽  
Seismic Waves ◽  
Three Dimensional ◽  
Time History ◽  
Economic Benefits ◽  
Seismic Structure ◽  
Finite Element Program ◽  
Concrete Frame ◽  
Element Program ◽  
Lateral Displacements

In this paper, the models of traditional anti-seismic and base-isolated masonry and concrete frame composite structures were created by the three-dimensional finite element program and their time history responses were analyzed under the actions of different seismic waves. The results show that whether they were under the action of frequently occurred earthquake or rarely occurred earthquake, the story shears of base-isolated structure are far less than those of traditional anti-seismic structure; the lateral displacements of the former are nearly translational, while those of the latter are approximately parabolic; and the fundamental period of the former is much longer than the counterpart. In conclusion, the seismic fortification intensity of base-isolated structure is one or two degree less than that of traditional anti-seismic structure, and adopting the base-isolated structure will protect the life-safety and property of people and achieve good economic benefits as well.

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