Shear Wave Generation From Contained Explosions
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Shear Wave Generation From Contained Explosions
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Author :
language : en
Publisher:
Release Date : 1996
Shear Wave Generation From Contained Explosions written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1996 with categories.
The usefulness of the amplitude ratio of seismic phases such as Lg/P, as well as the ratio of magnitudes to discriminate explosions from earthquakes depends, in part, on the efficiency of shear wave production from seismic sources. We are studying shear wave generation at the source, initially from explosions within limestone blocks. Initially the samples are subjected to hydrostatic stress. However, we will be able to also simulate tectonic strain energy release in future experiments. Using a 1.6m long, 0.8m diameter sample subjected to an ambient pressure of up to 1 MPa, with a centrally placed explosive source, we propose to study the amplitude of shear wave generation of stress wave induced radial cracking in symmetric and asymmetric cavities. In unstressed rock, this shear wave production is expected to be controlled in part by the natural anisotropy of the rock. We expect to measure the SIP ratio from tamped explosions using (0.2 to 2 gram charges). Later tests will be conducted in partially decoupled asymmetric cavities, and the resultant shear wave radiation pattern will be compared to previous detailed finite element calculations of P and S wave radiation versus frequency and angle for elliptical cavities of aspect ratios in the range of 1:3 to 1:10. In order to measure the P and S waves generated from explosions, we developed a measurement method that is given in detail in this report. The initial test results for the tamped and decoupled explosions in cylindrical cavities in limestone show that the amplitude of SV/P for the decoupled experiment in limestone is -0.7, whereas it varies over a range of -1 to 3 for overdriven cavities, depending on angle from the cylindrical axis. Moreover, tensional cracks are generated in these cavities which resemble those inferred to have occurred in a similar geometry in the Sterling experiment.
Shear Wave Generation By Decoupled And Partially Coupled Explosions
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Author :
language : en
Publisher:
Release Date : 2008
Shear Wave Generation By Decoupled And Partially Coupled Explosions written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
The objective of this project is to investigate the sources of shear wave generation by decoupled and partially coupled explosions, and the differences in shear wave generation between tamped and decoupled explosions. A perfectly spherical explosion at the center of a perfectly spherical cavity large enough to fully decouple the explosion would generate no shear waves, so all shear waves from decoupled explosions are due to asymmetries in and near the cavity, and to scattering and conversions. We quantify the effect of different sources of asymmetry through numerical modeling, and take advantage of unique features of different data sets to eliminate particular mechanisms and so constrain the possible sources of observed shear waves. We present numerical calculations, and analytic solutions for different pressure functions, of the problem of shear wave generation by an explosion offset from the center of a spherical cavity, which causes the shock wave to vary in amplitude and arrival time around the cavity surface. The offset explosion has a dipole component and can generate significant shear waves with a modest offset from the center. The numerical calculations produce cavity reverberations that are strongest along the axis of the source offset. We develop a physically reasonable pressure function that models the pressure reverberations and show that it leads to longer duration waveforms with more low frequency content, again with a dominant dipole contribution. We have shown previously that the radiation pattern of the near field, initial, shear-wave arrivals from the decoupled explosion Sterling could be reproduced by modeling that included the flat floor (due to melted and recrystallized salt) of the cavity. The observations also have substantial coda, which are not reproduced by the calculations. Similarity of coda waveforms with distance indicates their source is at or very near the cavity.
Analysis Of Shear Wave Generation By Decoupled And Partially Coupled Explosions
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Author :
language : en
Publisher:
Release Date : 2009
Analysis Of Shear Wave Generation By Decoupled And Partially Coupled Explosions written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
We compare near field and local seismograms from partially and fully decoupled chemical and nuclear explosions, and water-filled cavity nuclear explosions, with seismograms from tamped explosions in the same source location, and compare records of a centered and an offset explosion in a spherical cavity, all to identify and characterize shear waves generated by decoupled explosions. We numerically model the shear wave generation due to hydrofracturing, opening of pre-existing cracks, asymmetric nonlinear deformation outside the cavity due to only partial decoupling, offset of the source within the cavity, ellipticity of the cavity, and a flat-floored cavity (due to recrystalization of melted salt), and compare the simulations with observations. We also model an offset source analytically to investigate the effect of longer lasting reverberations. The observations and modeling indicate that partially and fully decoupled explosions generate significant shear wave energy at the source through various source asymmetries, including offset of the source and aspherical cavity shape.
Quantification Of Rock Damage From Small Explosions And Its Effect On Shear Wave Generation
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Author :
language : en
Publisher:
Release Date : 2009
Quantification Of Rock Damage From Small Explosions And Its Effect On Shear Wave Generation written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Weston Geophysical Corp., New England Research, Inc., and several geotechnical consultants conducted the Vermont/New England Damage Experiment in central Vermont during July 2008. A series of five explosions using charges with yields of 135 and 270 lbs and three types of explosives were detonated in homogeneous, low fracture density granite. The goal of the experiment was to generate different amounts of rock damage around the source by using explosives with dramatically different velocities of detonation (VOD), and then relate the shear wave generation to the amount of damage. We used pre- and post-shot core analysis to quantify significant differences in the damage induced by the explosions. Velocities are slower, permeabilities are higher, resistivities are lower, and porosities are higher in the damaged intervals. These results are consistent with a microcrack scale fracture population that is enhanced by the blasts. Over 140 seismic sensors were installed to record the blasts. Peak particle velocity (PPV) studies found that the fastest VOD explosive, Composition B, expended much of its energy at the source pulverizing the surrounding rock, while the middle VOD explosive, heavy ANFO, produced the largest PPV. Source scaling studies found the black powder shot produced seismic amplitudes up to an order of magnitude less than the ANFO and COMP B amplitudes above 5 Hz, but created Rayleigh waves similar in amplitude to those from the ANFO shot. The black powder shot produced larger Rayleigh and Love waves than the COMP B shot. The ANFO and COMP B shots generated similar amplitudes above 8 Hz, but the ANFO source Rayleigh waves were up to twice as large and the Love waves were up to three times as large as those from the COMP B shot. These results indicate that rock damage may be responsible for some of the differences in surface and shear wave generation.
High Frequency Shear Wave Generation At Pre Existing Cracks
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Author : R. S. Jih
language : en
Publisher:
Release Date : 1995
High Frequency Shear Wave Generation At Pre Existing Cracks written by R. S. Jih and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1995 with categories.
Recent observational studies indicate that, relative to decoupled explosions, tamped explosions tend to have a larger high frequency Lg/P ratio. Discrimination using such ratios is promising, and yet little is known about the basis for this discriminant. Improved fundamental understanding of the reasons this discriminant may be successful is desired. A plausible explanation offered by Blandford (19S5) is that tamped explosions generate more high-frequency S waves due to the cracks in the source region.
Generation Of Horizontally Polarized Shear Waves By Underground Explosions
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Author : Michael John Randall
language : en
Publisher:
Release Date : 1962
Generation Of Horizontally Polarized Shear Waves By Underground Explosions written by Michael John Randall and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1962 with Explosions categories.
Shear Wave Generation Of Near Surface Spall
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Author : Eric Rinehart
language : en
Publisher:
Release Date : 1984
Shear Wave Generation Of Near Surface Spall written by Eric Rinehart and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1984 with categories.
History Of Shock Waves Explosions And Impact
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Author : Peter O. K. Krehl
language : en
Publisher: Springer Science & Business Media
Release Date : 2008-09-24
History Of Shock Waves Explosions And Impact written by Peter O. K. Krehl and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008-09-24 with Science categories.
This unique and encyclopedic reference work describes the evolution of the physics of modern shock wave and detonation from the earlier and classical percussion. The history of this complex process is first reviewed in a general survey. Subsequently, the subject is treated in more detail and the book is richly illustrated in the form of a picture gallery. This book is ideal for everyone professionally interested in shock wave phenomena.
Wave Propagation From Complex 3d Sources Using The Representation Theorem
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Author :
language : en
Publisher:
Release Date : 2008
Wave Propagation From Complex 3d Sources Using The Representation Theorem written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
In spite of extensive prior research on the generation of seismic waves by underground nuclear explosions, it is still not possible to provide a complete explanation for the observed wavefields, particularly at regional distances. Spherically symmetric explosion models embedded in layered elastic media effectively model the P phases generated by explosions and the major characteristics of some reflected and transmitted phases. Nonlinear axisymmetric finite difference calculations of explosions, including gravity and the effect of the free surface, can model a more realistic explosion source that directly generated shear waves. These models explain more characteristics of explosion-generated seismic waves, including some aspects of regional shear phases. However, it is clear that linear and nonlinear near-source 3D effects are important in many cases. SH waves are commonly observed within a few kilometers of explosions, too close to have been generated by (simple) conversion of vertical and radial components, and often larger than those components. Furthermore, it has not been established what impact 3D effects have on discriminants and on explosion yield estimates. It is important, therefore, to be able to model and understand how 3D source and source region heterogeneity affect the seismic wavefield and what impact this has on parameters used for nuclear monitoring. In this new project, we are implementing a technique that allows us to propagate the results of near-source 3D finite difference calculations to regional and teleseismic distances, and to use the results to investigate the impact of 3D near-source effects on regional and teleseismic phases, focusing in particular on the generation of SH phases by explosion sources. Our approach is to perform 3D explosion source region calculations, and then to propagate the wavefield to local, regional and teleseismic distances using layered earth Green's functions.
Blast Waves
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Author : Charles E. Needham
language : en
Publisher: Springer Science & Business Media
Release Date : 2010-03-17
Blast Waves written by Charles E. Needham and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010-03-17 with Technology & Engineering categories.
As an editor of the international scienti?c journal Shock Waves, I was asked whether I might document some of my experience and knowledge in the ?eld of blast waves. I began an outline for a book on the basis of a short course that I had been teaching for several years. I added to the outline, ?lling in details and including recent devel- ments, especially in the subjects of height of burst curves and nonideal explosives. At a recent meeting of the International Symposium on the Interaction of Shock Waves, I was asked to write the book I had said I was working on. As a senior advisor to a group working on computational ?uid dynamics, I found that I was repeating many useful rules and conservation laws as new people came into the group. The transfer of knowledge was hit and miss as questions arose during the normal work day. Although I had developed a short course on blast waves, it was not practical to teach the full course every time a new member was added to the group. This was suf?cient incentive for me to undertake the writing of this book. I cut my work schedule to part time for two years while writing the book. This allowed me to remain heavily involved in ongoing and leading edge work in hydrodynamics while documenting this somewhat historical perspective on blast waves.