Effects of free-surface topography on moving-seismic-source modeling

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. T159-T166 ◽  
Author(s):  
Stig Hestholm ◽  
Mark Moran ◽  
Stephen Ketcham ◽  
Thomas Anderson ◽  
Meindert Dillen ◽  
...  
Keyword(s):  
Free Surface ◽  
Surface Topography ◽  
Plane Surface ◽  
Seismic Source ◽  
Source Modeling ◽  
Long Duration ◽  
Strong Material ◽  
Spatial Focusing ◽  
Amplitude Amplification ◽  
Strong Contrast

A curved-grid velocity-stress formulation for viscoelastic wave modeling is used with an arbitrary number of relaxation mechanisms to model a desired [Formula: see text]-behavior. These equations are discretized by high-order staggered finite differences (FDs) in the interior of the medium, and we gradually reduce the FD order to two at the stress-free surface, where we implement our boundary conditions for an arbitrary topographic surface. A moving source is simulated along the surface of a relatively general and locally steep surface topography and, for comparison, along a plane surface. The topography consists of a significant hill surrounded by a valley. Similar two-layered geologic models are used with both topographic surfaces, with the upper layer being a lossy sedimentary layer having a relatively strong contrast with the lower, higher-velocity half-space. Local topographic highs create varying amplitude amplifications at different times during motion of the source. A pronounced wavefield accumulation is evident at the topographic highs in all components. This is very different from the even pattern produced by the same source along the same path for the plane topographic surface, even in the presence of the strong material discontinuity between the two geologic layers. The effect is, however, similar to real records for nonmoving sources of long duration; over time, the direction of incidence becomes less significant, and amplitude amplification occurs in all directions for waves trapped in a topographic high. These spatial focusing effects should be taken into account in inversion for vehicle tracking to avoid target mislocation and/or misidentification.

Effects of free surface topography on moving seismic source modeling

2006 ◽  
Author(s):  
Stig Hestholm ◽  
Menno Dillen ◽  
George McMechan ◽  
Mark Moran ◽  
Stephen Ketcham ◽  
...  
Keyword(s):  
Free Surface ◽  
Surface Topography ◽  
Seismic Source ◽  
Source Modeling

Transient and sustained processing of musical consonance in auditory cortex and the effect of musicality

2020 ◽  
Vol 123 (4) ◽  
pp. 1320-1331 ◽  
Author(s):  
Martin Andermann ◽  
Roy D. Patterson ◽  
André Rupp
Keyword(s):  
Auditory Cortex ◽  
Physiological Activity ◽  
Stimulus Onset ◽  
Auditory Evoked Potential ◽  
Source Analysis ◽  
Source Modeling ◽  
Sustained Activity ◽  
Long Duration ◽  
Musical Sounds ◽  
N1 Wave

In recent years, electroencephalography and magnetoencephalography (MEG) have both been used to investigate the response in human auditory cortex to musical sounds that are perceived as consonant or dissonant. These studies have typically focused on the transient components of the physiological activity at sound onset, specifically, the N1 wave of the auditory evoked potential and the auditory evoked field, respectively. Unfortunately, the morphology of the N1 wave is confounded by the prominent neural response to energy onset at stimulus onset. It is also the case that the perception of pitch is not limited to sound onset; the perception lasts as long as the note producing it. This suggests that consonance studies should also consider the sustained activity that appears after the transient components die away. The current MEG study shows how energy-balanced sounds can focus the response waves on the consonance-dissonance distinction rather than energy changes and how source modeling techniques can be used to measure the sustained field associated with extended consonant and dissonant sounds. The study shows that musical dyads evoke distinct transient and sustained neuromagnetic responses in auditory cortex. The form of the response depends on both whether the dyads are consonant or dissonant and whether the listeners are musical or nonmusical. The results also show that auditory cortex requires more time for the early transient processing of dissonant dyads than it does for consonant dyads and that the continuous representation of temporal regularity in auditory cortex might be modulated by processes beyond auditory cortex. NEW & NOTEWORTHY We report a magnetoencephalography (MEG) study on transient and sustained cortical consonance processing. Stimuli were long-duration, energy-balanced, musical dyads that were either consonant or dissonant. Spatiotemporal source analysis revealed specific transient and sustained neuromagnetic activity in response to the dyads; in particular, the morphology of the responses was shaped by the dyad’s consonance and the listener’s musicality. Our results also suggest that the sustained representation of stimulus regularity might be modulated by processes beyond auditory cortex.

A pilot study of scoliosis assessment using radiation free surface topography in children with GMFCS IV and V cerebral palsy

2011 ◽  
Vol 38 (6) ◽  
pp. 854-862 ◽  
Author(s):  
S. Sadani ◽  
C. Jones ◽  
A. Seal ◽  
B. Bhakta ◽  
R. Hall ◽  
...  
Keyword(s):  
Cerebral Palsy ◽  
Free Surface ◽  
Pilot Study ◽  
Surface Topography

Concept and Fundamentals of Temporal-Spatial Pulse Representation for Dislocation Source Modeling

2004 ◽  
Vol 71 (6) ◽  
pp. 887-893
Author(s):  
Ray Ruichong Zhang
Keyword(s):  
Wave Motion ◽  
Seismic Source ◽  
Separation Distance ◽  
Point Of View ◽  
Mathematical Representation ◽  
Far Field ◽  
Source Modeling ◽  
Dislocation Source ◽  
Two Factors ◽  
Field Wave

For far-field wave-motion response to a point dynamic dislocation source, the temporal and spatial features of the source mechanism are characterized, respectively, by two factors, i.e., a source time function for dislocation growth and a combination of nine couples of impulse forces that is equivalent to the final dislocation. The mathematical representation for each of the couples, referred to as spatial couples, is a couple of impulses acting in opposing directions with an infinitesimal separation distance or, in the limit, by the derivative of the impulse with respect to the separation-distance parameter. This study proposes a temporal-spatial pulse representation for the nine couples, referred to as temporal-spatial couples, and subsequently for the dislocation source modeling. Each temporal-spatial couple consists of two impulses acting in opposite directions with both an infinitesimal separation distance and an infinitesimal time delay. By examining dynamite source modeling, this study shows that the proposed representation can intrinsically integrate the spatial and temporal features of the dislocation sources from the response point of view. This study also shows an example of a point, shear-slip seismic source modeling using traditional and proposed pulse representations for far-field wave motion. Discussion is finally provided for the implications of the proposed representation in broad applications.

Acoustic wave propagation in tilted transversely isotropic media: Incorporating topography

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. C265-C278 ◽  
Author(s):  
Jeffrey Shragge
Keyword(s):  
Wave Propagation ◽  
Free Surface ◽  
Surface Topography ◽  
Domain Boundary ◽  
Waveform Inversion ◽  
Transversely Isotropic ◽  
Surface Boundary ◽  
Reverse Time ◽  
Time Migration ◽  
Tti Media

Simulating two-way acoustic wavefield propagation directly from a free-surface boundary in the presence of topography remains a computational challenge for applications of reverse time migration (RTM) or full-waveform inversion (FWI). For land-seismic settings involving heavily reworked geology (e.g., fold and thrust belts), two-way wavefield propagation operators should also handle commonly observed complex anisotropy including tilted transversely isotropic (TTI) media. To address these issues, I have extended a system of coupled partial differential equations used to model 3D acoustic TTI wave propagation in Cartesian coordinates to more generalized 3D geometries, including a deformed computational mesh with a domain boundary conformal to free-surface topography. A generalized curvilinear transformation is used to specify a system of equations governing 3D acoustic TTI wave propagation in the “topographic” coordinate system. The developed finite-difference time-domain numerical solution adapts existing Cartesian TTI operators to this more generalized geometry with little additional computational overhead. Numerical evaluations illustrate that 2D and 3D impulse responses are well-matched to those simulated on Cartesian meshes and analytic traveltimes for homogeneous elliptical TTI media. Accordingly, these generalized acoustic TTI propagators and their numerical adjoints are useful for undertaking most RTM or FWI applications using computational domains conforming to free-surface topography.

Tensorial elastodynamics for isotropic media

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. T359-T373
Author(s):  
Jeffrey Shragge ◽  
Tugrul Konuk
Keyword(s):  
Free Surface ◽  
Surface Topography ◽  
Numerical Solutions ◽  
Waveform Inversion ◽  
Real Life ◽  
Staggered Grid ◽  
Surface Boundary ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration

Numerical solutions of 3D isotropic elastodynamics form the key computational kernel for many isotropic elastic reverse time migration and full-waveform inversion applications. However, real-life scenarios often require computing solutions for computational domains characterized by non-Cartesian geometry (e.g., free-surface topography). One solution strategy is to compute the elastodynamic response on vertically deformed meshes designed to incorporate irregular topology. Using a tensorial formulation, we have developed and validated a novel system of semianalytic equations governing 3D elastodynamics in a stress-velocity formulation for a family of vertically deformed meshes defined by Bézier interpolation functions between two (or more) nonintersecting surfaces. The analytic coordinate definition also leads to a corresponding analytic free-surface boundary condition (FSBC) as well as expressions for wavefield injection and extraction. Theoretical examples illustrate the utility of the tensorial approach in generating analytic equations of 3D elastodynamics and the corresponding FSBCs for scenarios involving free-surface topography. Numerical examples developed using a fully staggered grid with a mimetic finite-difference formulation demonstrate the ability to model the expected full-wavefield behavior, including complex free-surface interactions.

scholarly journals Stereoscopic and velocimetric reconstructions of the free surface topography of antidune flows

2005 ◽  
Vol 39 (3) ◽  
pp. 535-553 ◽  
Author(s):  
D. Douxchamps ◽  
D. Devriendt ◽  
H. Capart ◽  
C. Craeye ◽  
B. Macq ◽  
...  
Keyword(s):  
Free Surface ◽  
Surface Topography
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