A simultaneous inversion of seismic traveltimes and amplitudes for velocity and attenuation

Geophysics ◽  
1996 ◽  
Vol 61 (6) ◽  
pp. 1738-1757 ◽  
Author(s):  
Don W. Vasco ◽  
John E. Peterson ◽  
Ernest L. Majer
Keyword(s):  
Perturbation Approach ◽  
Well Log ◽  
Ray Theory ◽  
Fracture Zones ◽  
Low Velocity ◽  
Simultaneous Inversion ◽  
Attenuation Structure ◽  
Paraxial Ray ◽  
The Relationship ◽  
Velocity Region

It is possible to efficiently use traveltime and amplitude information to infer variations in velocity and Q. With little additional computation, terms accounting for source radiation pattern and receiver coupling may be included in the inversion. The methodology is based upon a perturbation approach to paraxial ray theory. The perturbation approach linearizes the relationship between velocity deviations and traveltime and amplitude anomalies. Using the technique, we infer the velocity and attenuation structure at a fractured granitic site near Raymond, California. A set of four well pairs are examined and each is found to contain two zones of strong attenuation. The velocity variations contain an upper low velocity region corresponding to the uppermost attenuating zone. The location of these zones agrees with independent well‐log and geophysical data. The velocity and attenuation anomalies appear to coincide with extensively fractured sections of the borehole and may indicate fracture zones rather than individual fractures.

The relationship of seat backrest angle and neck injury in low-velocity rear impacts

2005 ◽  
Vol 219 (11) ◽  
pp. 1293-1302 ◽  
Author(s):  
J Latchford ◽  
E C Chirwa ◽  
T Chen ◽  
M Mao
Keyword(s):  
Close Correlation ◽  
Neck Injury ◽  
Low Velocity ◽  
Cervical Spine Injuries ◽  
Rear Impact ◽  
Test Specifications ◽  
Lower Neck ◽  
Rear Impacts ◽  
Relationship Of ◽  
The Relationship

Car-rear-impact-induced cervical spine injuries present a serious burden on society and, in response, seats offering enhanced protection have been introduced. Seats are evaluated for neck protection performance but only at one specific backrest angle, whereas in the real world this varies greatly owing to the variation in occupant physique. Changing the backrest angle modifies the seat geometry and thereby the nature of its interaction with the occupant. Low-velocity rear-impact tests on a BioRID II anthropomorphic test dummy (ATD) have shown that changes in backrest angle have a significant proportionate effect on dummy kinematics. A close correlation was found between changes in backrest angle and the responses of neck injury predictors such as lower neck loading and lower neck shear but not for the neck injury criterion NICmax. Torso ramping was evident, however, with negligible effect in low-velocity impacts. The backrest angle ranged from 20° to 30° whereas the BioRID II spine was adapted to a range from 20° to 26.5°. Nevertheless, in general, instrumentation outputs correlated well, indicating that this ATD could be used for evaluating seats over a 20–30° range rather than solely at 25° as required by current approval test specifications.

scholarly journals Structure of accretion flows in the nova-like cataclysmic variable RW Tri

2020 ◽  
Vol 497 (2) ◽  
pp. 1475-1487
Author(s):  
G Subebekova ◽  
S Zharikov ◽  
G Tovmassian ◽  
V Neustroev ◽  
M Wolf ◽  
...  
Keyword(s):  
Binary Systems ◽  
Cataclysmic Variable ◽  
Low Velocity ◽  
Time Resolved ◽  
Narrow Component ◽  
Accretion Flows ◽  
Photometric Observations ◽  
Hα Emission ◽  
Usual Interpretation ◽  
Velocity Region

ABSTRACT We obtained photometric observations of the nova-like (NL) cataclysmic variable RW Tri and gathered all available AAVSO and other data from the literature. We determined the system parameters and found their uncertainties using the code developed by us to model the light curves of binary systems. New time-resolved optical spectroscopic observations of RW Tri were also obtained to study the properties of emission features produced by the system. The usual interpretation of the single-peaked emission lines in NL systems is related to the bi-conical wind from the accretion disc’s inner part. However, we found that the Hα emission profile is comprised of two components with different widths. We argue that the narrow component originates from the irradiated surface of the secondary, while the broader component’s source is an extended, low-velocity region in the outskirts of the accretion disc, located opposite to the collision point of the accretion stream and the disc. It appears to be a common feature for long-period NL systems – a point we discuss.

Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Compressional Wave ◽  
Bright Spot ◽  
Low Velocity ◽  
Gas Reservoir ◽  
Gas Field ◽  
Compressional Waves ◽  
The Relationship

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

Ground‐penetrating radar velocity tomography in heterogeneous and anisotropic media

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1758-1773 ◽  
Author(s):  
Don W. Vasco ◽  
John E. Peterson ◽  
Ki Ha Lee
Keyword(s):  
Ground Penetrating Radar ◽  
Electromagnetic Waves ◽  
Numerical Technique ◽  
Anisotropic Media ◽  
Perturbation Approach ◽  
Low Velocity ◽  
Weak Anisotropy ◽  
Geological Features ◽  
Velocity Anomalies ◽  
Ground Penetrating

A ray series solution for Maxwell's equations provides an efficient numerical technique for calculating wavefronts and raypaths associated with electromagnetic waves in anisotropic media. Using this methodology and assuming weak anisotropy, we show that a perturbation of the anisotropic structure may be related linearly to a variation in the traveltime of an electromagnetic wave. Thus, it is possible to infer lateral variations in the dielectric permittivity and magnetic permeability matrices. The perturbation approach is used to analyze a series of crosswell ground‐penetrating radar surveys conducted at the Idaho National Engineering Laboratory. Several important geological features are imaged, including a rubble zone at the interface between two basalt flows. Linear low‐velocity anomalies are imaged clearly and are continuous across well pairs.

A SIMPLE UPGRADE FOR SOME BRIGHT SPOTS

Geophysics ◽  
1977 ◽  
Vol 42 (4) ◽  
pp. 868-871 ◽  
Author(s):  
Jerry A. Ware
Keyword(s):  
Constant Velocity ◽  
Bright Spot ◽  
Ray Theory ◽  
Multiple Reflections ◽  
Low Velocity ◽  
Reasonable Estimate ◽  
Raw Data ◽  
Common Depth Point ◽  
Bright Spots ◽  
The Common

Confirmation that a bright spot zone in question is low velocity can sometimes be made by looking at constant velocity stacks or the common‐depth‐point gathers. When this confirmation does exist, then it is usually possible to do simple ray theory to get a reasonable estimate of the pay thickness, especially if the water‐sand velocity and the gas‐sand velocity are either known or can be predicted for the area. The confirmation referred to can take the form of under‐removal of the primary events or be exhibited by multiple reflections from the bright spot zone. Such under‐removals or multiple reflections will not be seen on the stacked sections but are sometimes obvious on the raw data, such as the common‐depth‐point gathers, or can be implied by looking at constant velocity stacks of the zone in question at different stacking velocities.

scholarly journals A three-dimensional study of a crustal low velocity region beneath the 9°03′N overlapping spreading center

2003 ◽  
Vol 30 (2) ◽  
Author(s):  
S. Bazin ◽  
A. J. Harding ◽  
G. M. Kent ◽  
J. A. Orcutt ◽  
S. C. Singh ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Spreading Center ◽  
Low Velocity ◽  
Velocity Region

Research Progress in High Velocity Penetration into Concrete Theory

2013 ◽  
Vol 405-408 ◽  
pp. 2487-2491
Author(s):  
Cun Cheng Shi ◽  
Xin Fan ◽  
Sheng Guo Zou ◽  
Meng Shen Li
Keyword(s):  
Material Properties ◽  
High Velocity ◽  
Target Material ◽  
Low Velocity Impact ◽  
Research Progress ◽  
Future Research ◽  
Low Velocity ◽  
The Earth ◽  
Hypervelocity Penetration ◽  
Velocity Region

With the development of the earth penetration weapon, the research interest has gradually changed from low velocity impact to high velocity or hypervelocity penetration. This paper reviews the the theoretic research status on velocity region ascertaining of penetration, the target material properties near penetration cavity and mass abrasion of projectiles in high velocity penetration, and makes suggestions on the future research.

3-D true‐amplitude finite‐offset migration

Geophysics ◽  
1993 ◽  
Vol 58 (8) ◽  
pp. 1112-1126 ◽  
Author(s):  
Jorg Schleicher ◽  
Martin Tygel ◽  
Peter Hubral
Keyword(s):  
Weight Function ◽  
A Priori ◽  
Three Dimensional ◽  
Reflection Coefficients ◽  
Ray Theory ◽  
Geometrical Spreading ◽  
Spreading Factor ◽  
Prestack Migration ◽  
The One ◽  
Paraxial Ray

Compressional primary nonzero offset reflections can be imaged into three‐dimensional (3-D) time or depth‐migrated reflections so that the migrated wavefield amplitudes are a measure of angle‐dependent reflection coefficients. Various migration/inversion algorithms involving weighted diffraction stacks recently proposed are based on Born or Kirchhoff approximations. Here a 3-D Kirchhoff‐type prestack migration approach is proposed where the primary reflections of the wavefields to be imaged are a priori described by the zero‐order ray approximation. As a result, the principal issue in the attempt to recover angle‐dependent reflection coefficients becomes the removal of the geometrical spreading factor of the primary reflections. The weight function that achieves this aim is independent of the unknown reflector and correctly accounts for the recovery of the source pulse in the migrated image irrespective of the source‐receiver configurations employed and the caustics occurring in the wavefield. Our weight function, which is computed using paraxial ray theory, is compared with the one of the inversion integral based on the Beylkin determinant. It differs by a factor that can be easily explained.

Hot-Wire Measurements Inside a Centrifugal Fan Impeller

1989 ◽  
Vol 111 (4) ◽  
pp. 363-368 ◽  
Author(s):  
A. Kjo¨rk ◽  
L. Lo¨fdahl
Keyword(s):  
Suction Side ◽  
Design Flow ◽  
Shear Stresses ◽  
Centrifugal Fan ◽  
Reynolds Stresses ◽  
Low Velocity ◽  
Mean Velocity ◽  
Attached Flow ◽  
The Mean ◽  
Velocity Region

Measurements of the three mean velocity components and five of the Reynolds stresses have been carried out in the blade passage of a centrifugal fan impeller. The impeller was of ordinary design, with nine backward curved blades, and all measurements were carried out at the design flow rate. The mean velocity measurements show that the flow can be characterized as an attached flow with almost linearly distributed velocity profiles. However, in a region near the suction side close to the shroud a low velocity region is created. From the turbulence measurements it can be concluded that relatively low values of the turbulent stresses are predominating in the center region of the channel. Closer to the walls higher values of the normal as well as shear stresses are noted.

Imaging of reflection seismic energy for mapping shallow fracture zones in crystalline rocks

Geophysics ◽  
1994 ◽  
Vol 59 (5) ◽  
pp. 753-765 ◽  
Author(s):  
J. S. Kim ◽  
Wooil M. Moon ◽  
Ganpat Lodha ◽  
Mulu Serzu ◽  
Nash Soonawala
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Incidence Angle ◽  
Seismic Energy ◽  
Crystalline Rock ◽  
Crystalline Rocks ◽  
Fracture Zones ◽  
Low Velocity ◽  
Amplitude Noise ◽  
Reflection Seismic

The high‐resolution reflection seismic technique is being used increasingly to address geologic exploration and engineering problems. There are, however, a number of problems in applying reflection seismic techniques in a crystalline rock environment. The reflection seismic data collected over a fractured crystalline rock environment are often characterized by low signal‐to‐noise ratios (S/N) and inconsistent reflection events. Thus it is important to develop data processing strategies and correlation schemes for the imaging of fracture zones in crystalline rocks. Two sets of very low S/N, high‐resolution seismic data, previously collected by two different contractors in Pinawa, Canada, and the island of Äspö, Sweden, were reprocessed and analyzed, with special emphasis on the shallow reflection events occurring at depths as shallow as 60–100 m. The processing strategy included enhancing the signals hidden behind large‐amplitude noise, including clipped ground roll. The pre‐ and poststack processing includes shot f-k filtering, residual statics, careful muting after NMO correction, energy balance, and coherency filtering. The final processed seismic sections indicate that reflected energy in these data sets is closely related to rock quality in Äspö data and fracturing in Atomic Energy of Canada, Ltd. (AECL) data. The lithologic boundaries are not clearly mappable in these data. When thickness of the reflection zone is of the order of a wavelength, the top and bottom of the zone may be resolved. The major fracture zones in crystalline rocks correlate closely with the well‐log data and are usually characterized by very low velocity and produce low‐acoustic‐impedance contrasts compared to those of surrounding rocks. Because the incidence angles vary rapidly for shallow‐reflection geometries, segments of major fracture zones can effectively be analyzed in terms of reflectivity. Reflection images of each fracture zone were investigated in the common‐offset section, where each focused event was associated with a consistent incidence angle on the reflectivity map. The complex attributes of the data indicate that strong reflectors at shallow depth coincide with intensely fractured zones. These correlate well with instantaneous amplitude plots and instantaneous frequency plots. The instantaneous phase plot also identifies the major and minor fractures.

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