Effect of Random 3D Correlated Velocity Perturbations on Numerical Modeling of Ground Motion from the Source Physics Experiment

2020 ◽  
Author(s):  
Michelle Scalise ◽  
Arben Pitarka ◽  
John N. Louie ◽  
Kenneth D. Smith
Keyword(s):  
Wave Propagation ◽  
Wave Scattering ◽  
Small Scale ◽  
Stochastic Perturbations ◽  
Near Surface ◽  
Velocity Models ◽  
Chemical Explosions ◽  
Shear Motion ◽  
Physics Experiment ◽  
Source Physics

ABSTRACT Explosions are traditionally discriminated from earthquakes, using the relative amplitude of compressional and shear waves at regional and teleseismic distances known as the P/S discriminant. Pyle and Walter (2019) showed this technique to be less robust at shorter distances, in detecting small-magnitude earthquakes and low-yield explosions. The disparity is largely due to ground motion from small, shallow sources being significantly impacted by near-surface structural complexities. To understand the implications of wave propagation effects in generation of shear motion and P/S ratio during underground chemical explosions, we performed simulations of the Source Physics Experiment (SPE) chemical explosions using 1D and 3D velocity models of the Yucca Flat basin. All simulations used isotropic point sources in the frequency range 0–5 Hz. We isolate the effect of large-scale geological structure and small-scale variability at shallow depth (<5  km), using a regional 3D geologic framework model (GFM) and the GFM-R model derived from the GFM, by adding correlated stochastic velocity perturbations. A parametric study of effects of small-scale velocity variations on wave propagation, computed using a reference 1D velocity model with stochastic perturbations, shows that the correlation length and depth of stochastic perturbations significantly impact wave scattering, near-surface wave conversions, and shear-wave generation. Comparisons of recorded and simulated waveforms for the SPE-5 explosion, using 3D velocity models, demonstrate that the shallow structure of the Yucca Flat basin contributes to generation of observed shear motion. The inclusion of 3D wave scattering, simulated by small-scale velocity perturbations in the 3D model, improves the fit between the simulated and recorded waveforms. In addition, a relatively low intrinsic attenuation, combined with small-scale velocity variations in our models, can confirm the observed wave trapping and its effect on duration of coda waves and the spatial variation of P/S ratio at basin sites.

Small-scale physical modeling of seismic-wave propagation using unconsolidated granular media

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. T323-T339 ◽  
Author(s):  
Ludovic Bodet ◽  
Amine Dhemaied ◽  
Roland Martin ◽  
Régis Mourgues ◽  
Fayçal Rejiba ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Physical Modeling ◽  
Granular Media ◽  
Laser Doppler Vibrometer ◽  
Seismic Wave Propagation ◽  
Acoustic Mode ◽  
Physical Models ◽  
Small Scale ◽  
Near Surface

Laboratory physical modeling and laser-based experiments are frequently proposed to tackle theoretical and methodological issues related to seismic prospecting, e.g., when experimental validations of processing or inversion techniques are required. Lasers are mainly used to simulate typical field acquisition setups on homogeneous and consolidated materials assembled into laboratory-scale physical models (PMs) of various earth structures. We suggested the use of granular materials to study seismic-wave propagation in unconsolidated and porous media and target near-surface exploration and hydrogeologic applications. We designed and tested the reproducibility of an experimental procedure to build and probe PMs consisting of micrometric glass beads (GBs). A mechanical source and a laser-Doppler vibrometer were used to record small-scale seismic lines at the surface of three GBs models. When guided surface acoustic mode theory should prevail in such unconsolidated granular packed structure under gravity, we only considered elastic-wave propagation in stratified media to interpret recorded data. Thanks to basic seismic processing and inversion methods (first arrivals and dispersion analyses), we were able to correctly retrieve the gradients of pressure- and shear-wave velocities in our models. A 3D elastic finite difference simulation of the experiment offered, despite significant differences in terms of amplitudes, a supplementary validation of our approximation, as far as elastic properties of the medium were concerned.

scholarly journals Velocity Structure at the Source Physics Experiment Phase I Site Obtained with the Large‐N Array Data

2019 ◽  
Vol 91 (1) ◽  
pp. 304-309
Author(s):  
Ting Chen ◽  
Catherine M. Snelson ◽  
Robert Mellors
Keyword(s):  
Velocity Structure ◽  
Volcanic Rocks ◽  
Velocity Model ◽  
Seismic Array ◽  
P Wave ◽  
Low Velocity ◽  
Large N ◽  
Chemical Explosions ◽  
Physics Experiment ◽  
Source Physics

Abstract The Source Physics Experiment (SPE) consists of a series of chemical explosions at the Nevada National Security Site. The goal of the SPE is to understand and model seismic‐wave generation and propagation from these explosions. To achieve this goal, we need an accurate velocity model of the SPE site. A large‐N seismic array deployed at the SPE site during one of the chemical explosions (SPE‐5) provides great data for this purpose. The array consists of 996 geophones and covers an area of approximately 2×2.5  km. In addition to the SPE‐5 explosion, the array recorded 53 large weight drops. Using the large‐N seismic array recordings, we perform first‐arrival analysis and obtain a 2D P‐wave velocity model of the SPE site. We image a sharp transition from high‐velocity Cretaceous granite to low‐velocity Quaternary alluvium. Other geological units such as the Tertiary volcanic rocks and Paleozoic sedimentary rocks are also clearly shown. The results of this work provide important local geological information and will be incorporated into the larger 3D modeling effort of the SPE program to validate the predictive models developed for the site.

scholarly journals Characterization of Spall in Hard Rock from Observations and Simulations of the Source Physics Experiment Phase I

2020 ◽  
Vol 110 (2) ◽  
pp. 596-612 ◽  
Author(s):  
Sean R. Ford ◽  
Oleg Y. Vorobiev
Keyword(s):  
Time History ◽  
Surface Force ◽  
Physical Force ◽  
Near Surface ◽  
Nuclear Explosions ◽  
Parameterized Model ◽  
Force Time ◽  
Physics Experiment ◽  
Source Physics

ABSTRACT Spall signals from the Source Physics Experiments are presented, analyzed, and modeled for insight to the explosion source. The observed signal is similar in nature to nearby historical nuclear explosions, and the surface force-time history or velocity can be interpreted with the same model. We use the models for peak spall velocity, spalled mass, and spall depth and radius derived from historical nuclear explosions to parameterize the physical force-time history model from Stump (1985) and show that this parameterized model can be used for spall prediction. The spall signal is also investigated with a numerical continuum model that incorporates gravity. Peak velocity and dwell time are well predicted, and the multiple slap-down phases are captured if one includes a weak near-surface layer similar to the geologic observation.

scholarly journals Source Separation and Medium Change of Contained Chemical Explosions from Coda Wave Interferometry

2021 ◽  
Vol 1 (1) ◽  
pp. 3-10
Author(s):  
Sean R. Ford ◽  
William R. Walter
Keyword(s):  
Coda Wave ◽  
Velocity Perturbation ◽  
Spherical Region ◽  
Seismic Coda ◽  
Chemical Explosions ◽  
Medium Change ◽  
Physics Experiment ◽  
Coda Wave Interferometry ◽  
Source Physics ◽  
Chemical Explosion

Abstract Differences in the seismic coda of neighboring events can be used to investigate source location offsets and medium change with coda wave interferometry (CWI). We employ CWI to infer the known relative location between two chemical explosions in Phase I of the Source Physics Experiment (SPE). The inferred displacement between the first, SPE-1, and second, SPE-2, chemical explosion is between 6 and 18 m, with an expectation of 9.2 m, where the known separation is close to 9.4 m. We also employ CWI to find any velocity perturbation due to damage from SPE-2, by comparing its coda with the collocated third SPE chemical explosion, SPE-3. We find that damage due to SPE-2 must be confined to a spherical region with radius less than 10 m and velocity perturbation less than 25%.

Uncertainty Propagation and Stochastic Interpretation of Shear Motion Generation due to Underground Chemical Explosions in Jointed Rock

2020 ◽  
Author(s):  
Souheil Ezzedine ◽  
Oleg Vorobiev ◽  
Tarabay Antoun ◽  
William Walter
Keyword(s):  
Wave Propagation ◽  
Near Field ◽  
Uncertainty Propagation ◽  
Source Zone ◽  
Underground Explosion ◽  
Zone Model ◽  
Far Field ◽  
Motion Generation ◽  
Chemical Explosions ◽  
Shear Motion

<p>We have performed 3D simulations of underground chemical explosions conducted recently in granitic outcrop as part of the Source Physics Experiment (SPE) campaign. The main goal of these simulations is to understand the nature of the shear motions recorded in the near field considering uncertainties in a) the geological characterization of the joints, such as density, orientation and persistency and b) the geomechanical material properties, such as, friction angle, bulk sonic speed, poroelasticity etc. The approach is probabilistic; joints are depicted using a Boolean stochastic representation of inclusions conditional to observations and their probability density functions inferred from borehole data. Then, using a novel continuum approach, joints and faults are painted into the continuum host material, granite. To ensure the fidelity of the painted joints we have conducted a sensitivity study of continuum vs. discrete representation of joints. Simulating wave propagation in heterogeneous discontinuous rock mass is a highly non-linear problem and uncertainty propagation via intrusive methods is practically forbidden. Therefore, using a series of nested Monte Carlo simulations, we have explored and propagated both the geological and the geomechanical uncertainty parameters. We have probabilistically shown that significant shear motions can be generated by sliding on the joints caused by spherical wave propagation. Polarity of the shear motion may change during unloading when the stress state may favor joint sliding on a different joint set. Although this study focuses on understanding shear wave generation in the near field, the overall goal of our investigation is to understand the far field seismic signatures associated with shear waves generated in the immediate vicinity of an underground explosion. Therefore, we have abstracted the near field behavior into a probabilistic source-zone model which is used in the far field wave propagation.</p><p>This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344</p>

Source Physics Experiment Phase II Dry Alluvium Geology (DAG) Experiments Design Reviews

2017 ◽  
Author(s):  
Peter Dickson ◽  
Gerald John Seitz ◽  
Kyle J. Deines ◽  
Robert C. Gentzlinger ◽  
Nathaniel Jordan Paul Mesick ◽  
...  
Keyword(s):  
Phase Ii ◽  
Physics Experiment ◽  
Source Physics

scholarly journals Velocity structure and radial anisotropy of the lithosphere in southern Madagascar from surface wave dispersion

2020 ◽  
Vol 224 (3) ◽  
pp. 1930-1944 ◽  
Author(s):  
E J Rindraharisaona ◽  
F Tilmann ◽  
X Yuan ◽  
J Dreiling ◽  
J Giese ◽  
...  
Keyword(s):  
Receiver Functions ◽  
Dispersion Curves ◽  
Eastern Coast ◽  
Small Scale ◽  
Seismic Structure ◽  
Lithospheric Thickness ◽  
Velocity Models ◽  
Phase Velocities ◽  
Maximum Value ◽  
Radial Anisotropy

SUMMARY We investigate the upper mantle seismic structure beneath southern Madagascar and infer the imprint of geodynamic events since Madagascar’s break-up from Africa and India and earlier rifting episodes. Rayleigh and Love wave phase velocities along a profile across southern Madagascar were determined by application of the two-station method to teleseismic earthquake data. For shorter periods (<20 s), these data were supplemented by previously published dispersion curves determined from ambient noise correlation. First, tomographic models of the phase velocities were determined. In a second step, 1-D models of SV and SH wave velocities were inverted based on the dispersion curves extracted from the tomographic models. As the lithospheric mantle is represented by high velocities we identify the lithosphere–asthenosphere boundary by the strongest negative velocity gradient. Finally, the radial anisotropy (RA) is derived from the difference between the SV and SH velocity models. An additional constraint on the lithospheric thickness is provided by the presence of a negative conversion seen in S receiver functions, which results in comparable estimates under most of Madagascar. We infer a lithospheric thickness of 110−150 km beneath southern Madagascar, significantly thinner than beneath the mobile belts in East Africa (150−200 km), where the crust is of comparable age and which were located close to Madagascar in Gondwanaland. The lithospheric thickness is correlated with the geological domains. The thinnest lithosphere (∼110 km) is found beneath the Morondava basin. The pre-breakup Karoo failed rifting, the rifting and breakup of Gondwanaland have likely thinned the lithosphere there. The thickness of the lithosphere in the Proterozoic terranes (Androyen and Anosyen domains) ranges from 125 to 140 km, which is still ∼30 km thinner than in the Mozambique belt in Tanzania. The lithosphere is the thickest beneath Ikalamavony domain (Proterozoic) and the west part of the Antananarivo domain (Archean) with a thickness of ∼150 km. Below the eastern part of Archean domain the lithosphere thickness reduces to ∼130 km. The lithosphere below the entire profile is characterized by positive RA. The strongest RA is observed in the uppermost mantle beneath the Morondava basin (maximum value of ∼9 per cent), which is understandable from the strong stretching that the basin was exposed to during the Karoo and subsequent rifting episode. Anisotropy is still significantly positive below the Proterozoic (maximum value of ∼5 per cent) and Archean (maximum value of ∼6 per cent) domains, which may result from lithospheric extension during the Mesozoic and/or thereafter. In the asthenosphere, a positive RA is observed beneath the eastern part Morondava sedimentary basin and the Proterozoic domain, indicating a horizontal asthenospheric flow pattern. Negative RA is found beneath the Archean in the east, suggesting a small-scale asthenospheric upwelling, consistent with previous studies. Alternatively, the relatively high shear wave velocity in the asthenosphere in this region indicate that the negative RA could be associated to the Réunion mantle plume, at least beneath the volcanic formation, along the eastern coast.

Interferometric imaging condition for wave-equation migration

Geophysics ◽  
2008 ◽  
Vol 73 (2) ◽  
pp. S47-S61 ◽  
Author(s):  
Paul Sava ◽  
Oleg Poliannikov
Keyword(s):  
Large Scale ◽  
Wigner Distribution ◽  
Random Noise ◽  
Velocity Model ◽  
Distribution Functions ◽  
Small Scale ◽  
Interferometric Imaging ◽  
Imaging Data ◽  
Imaging Condition ◽  
Velocity Models

The fidelity of depth seismic imaging depends on the accuracy of the velocity models used for wavefield reconstruction. Models can be decomposed in two components, corresponding to large-scale and small-scale variations. In practice, the large-scale velocity model component can be estimated with high accuracy using repeated migration/tomography cycles, but the small-scale component cannot. When the earth has significant small-scale velocity components, wavefield reconstruction does not completely describe the recorded data, and migrated images are perturbed by artifacts. There are two possible ways to address this problem: (1) improve wavefield reconstruction by estimating more accurate velocity models and image using conventional techniques (e.g., wavefield crosscorrelation) or (2) reconstruct wavefields with conventional methods using the known background velocity model but improve the imaging condition to alleviate the artifacts caused by the imprecise reconstruction. Wedescribe the unknown component of the velocity model as a random function with local spatial correlations. Imaging data perturbed by such random variations is characterized by statistical instability, i.e., various wavefield components image at wrong locations that depend on the actual realization of the random model. Statistical stability can be achieved by preprocessing the reconstructed wavefields prior to the imaging condition. We use Wigner distribution functions to attenuate the random noise present in the reconstructed wavefields, parameterized as a function of image coordinates. Wavefield filtering using Wigner distribution functions and conventional imaging can be lumped together into a new form of imaging condition that we call an interferometric imaging condition because of its similarity to concepts from recent work on interferometry. The interferometric imaging condition can be formulated both for zero-offset and for multioffset data, leading to robust, efficient imaging procedures that effectively attenuate imaging artifacts caused by unknown velocity models.

Sign in / Sign up

Export Citation Format

Share Document