Seismic monitoring of diffraction images for detection of local heterogeneities

Geophysics ◽  
1998 ◽  
Vol 63 (3) ◽  
pp. 1093-1100 ◽  
Author(s):  
Evgeny Landa ◽  
Shemer Keydar
Keyword(s):  
Seismic Signal ◽  
Seismic Monitoring ◽  
Surface Velocity ◽  
Radius Of Curvature ◽  
Seismic Section ◽  
Near Surface ◽  
Geological Processes ◽  
Diffracted Waves ◽  
The Media ◽  
Time Correction

Diffracted waves contain valuable information regarding both the structure and composition of the media they are in. In seismic data processing, however, these waves are usually regarded as noise. In this paper, we present an attempt to use scattered/diffracted waves for the detection of local heterogeneities. The method is based on the detection of diffracted waves by concentrating the signal amplitudes from diffracting points on the seismic section. This is done using a correlation procedure that enhances the amplitude of the seismic signal at the location of the diffractors on the common‐diffraction‐point section (D-section). The new local time correction for diffraction traveltime curve parameterization is based on the radius of curvature of the diffracted wavefront and near‐surface velocity. We use the idea of seismic monitoring for detection and delineating local objects which may occur within the subsurface resulting from human activity or fast geological processes. The method consists of continuous repetition of seismic experiments above an investigated area, constructing D-sections, and comparing the images obtained.

Diffraction imaging by multifocusing

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCA75-WCA81 ◽  
Author(s):  
Alex Berkovitch ◽  
Igor Belfer ◽  
Yehuda Hassin ◽  
Evgeny Landa
Keyword(s):  
Radius Of Curvature ◽  
Correct Identification ◽  
Local Velocity ◽  
Large Area ◽  
Seismic Section ◽  
Diffracted Waves ◽  
Diffraction Imaging ◽  
Time Correction ◽  
Two Parameters ◽  
Correlation Procedure

Correct identification of geologic discontinuities, such as faults, pinch-outs, and small-size scattering objects, is a primary challenge of the seismic method. Seismic response from these objects is encoded in diffractions. Our method images local heterogeneities of the subsurface using diffracted seismic events. The method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities. This is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local-time-correction formula to parameterize diffraction traveltime curves. This time correction, which is based on the multifocusing method, depends on two parameters: the emergent angle and the radius of curvature of the diffracted wavefront. These parameters are estimated directly from prestack seismic traces. The diffraction multifocusing stack (DMFS) can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area.

scholarly journals Physics-Based Relationship for Pore Pressure and Vertical Stress Monitoring Using Seismic Velocity Variations

2021 ◽  
Vol 13 (14) ◽  
pp. 2684
Author(s):  
Eldert Fokker ◽  
Elmer Ruigrok ◽  
Rhys Hawkins ◽  
Jeannot Trampert
Keyword(s):  
Pore Pressure ◽  
Seismic Velocity ◽  
Pressure Head ◽  
Groundwater Table ◽  
Surface Velocity ◽  
Seismic Velocities ◽  
Stress Monitoring ◽  
Near Surface ◽  
Velocity Variations ◽  
Velocity Changes

Previous studies examining the relationship between the groundwater table and seismic velocities have been guided by empirical relationships only. Here, we develop a physics-based model relating fluctuations in groundwater table and pore pressure with seismic velocity variations through changes in effective stress. This model justifies the use of seismic velocity variations for monitoring of the pore pressure. Using a subset of the Groningen seismic network, near-surface velocity changes are estimated over a four-year period, using passive image interferometry. The same velocity changes are predicted by applying the newly derived theory to pressure-head recordings. It is demonstrated that the theory provides a close match of the observed seismic velocity changes.

Surface-Wave Simulation for the Continuously Moving Seismic Sources

2021 ◽  
Author(s):  
Yuefeng Yan ◽  
Chengyu Sun ◽  
Tengfei Lin ◽  
Jiao Wang ◽  
Jidong Yang ◽  
...  
Keyword(s):  
Rayleigh Waves ◽  
Frequency Dispersion ◽  
Dispersion Curves ◽  
Velocity Estimation ◽  
Surface Velocity ◽  
Seismic Sources ◽  
Near Surface ◽  
Moving Source ◽  
Source Data ◽  
Doppler Effects

Abstract In exploration and earthquake seismology, most sources used in subsurface structure imaging and rock property estimation are fixed in certain positions. Continuously moving seismic sources, such as vehicles and the metro, are one kind of important passive sources in ambient noise research. Commonly, seismic data acquisition and processing for moving sources are based on the assumption of simple point passive sources, and the dispersion curve inversion is applied to constrain near-surface velocity. This workflow neglects the Doppler effects. Considering the continuously moving properties of the sources, we first derive the analytical solution for the Rayleigh waves excited by heavy vehicles and then analyze their Doppler effects and dispersion curves. We observe that the moving source data have the Doppler effect when compared with the changes in the frequency of the source intensity, but this effect does not affect the frequency dispersion of Rayleigh waves. The dispersion curves computed for moving source records are consistent with the analytical dispersion solutions, which provide a theoretical foundation for velocity estimation using moving source data.

AN APPROACH TO INVERSE FILTERING OF NEAR‐SURFACE LAYER EFFECTS FROM SEISMIC RECORDS

Geophysics ◽  
1961 ◽  
Vol 26 (6) ◽  
pp. 754-760 ◽  
Author(s):  
Pierre L. Goupillaud
Keyword(s):  
Surface Layer ◽  
Seismic Reflection ◽  
Normal Incidence ◽  
Resolving Power ◽  
Surface Velocity ◽  
Inverse Filtering ◽  
Near Surface ◽  
Seismic Records ◽  
Stratification Variable ◽  
Velocity Information

This paper suggests a scheme for compensating the effects that the near‐surface stratification, variable from spread to spread, produces on both the character and the timing of the seismic traces. For this purpose, accurate near‐surface velocity information is mandatory. This scheme should greatly reduce the correlation difficulties so frequently encountered in many areas. It may also be used to enhance the resolving power of the seismic reflection technique. The approach presented here is based on the rather restrictive assumptions of normal incidence, parallel equispaced plant reflectors, and noiseless conditions.

Residual Stress in Bone: A Parametric Study

2008 ◽  
Author(s):  
A. Hizal ◽  
B. Sadasivam ◽  
D. Arola
Keyword(s):  
Residual Stress ◽  
Particle Size ◽  
Residual Stresses ◽  
Material Removal ◽  
Surface Deformation ◽  
Radius Of Curvature ◽  
Near Surface ◽  
Size And Shape ◽  
Air Jet ◽  
Particle Size And Shape

A preliminary study was conducted to evaluate the parametric dependence of the residual stress distributions in bone that result from an abrasive air-jet surface treatment. Specifically, the influence of particle size and shape used in the treatment on the residual stress, propensity of embedding particles and material removal were studied. Rectangular beams of cortical bone were prepared from bovine femurs and treated with aluminum oxide and glass particles with different treatment angles. Residual stresses within the bone were quantified in terms of the radius of curvature of the bone specimens measured before and after the treatments, as well as a function of time to quantify decay in the stress. The sub-surface distribution was also examined using the layer removal technique. Results showed that the particle size and shape could be used to control the amount of material removal and the magnitude of residual stress within the treated surfaces. An increase in size of the glass particles resulted in an increase in the residual stress and a decrease in material removed during the treatment. The magnitude of residual stress ranged from 22 MPa to nearly 44 MPa through modulation of the particle qualities (size and shape). A microscopic examination of the treated surfaces suggests that the residual stresses resulted primarily from near-surface deformation.

Tracking of velocity variations at depth in the presence of surface velocity fluctuations

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. U1-U8 ◽  
Author(s):  
Benoit de Cacqueray ◽  
Philippe Roux ◽  
Michel Campillo ◽  
Stefan Catheline
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Surface Velocity ◽  
Small Scale ◽  
Beam Forming ◽  
Near Surface ◽  
Velocity Fluctuations ◽  
Wave Separation ◽  
Double Beam ◽  
Velocity Variations

We tested a small-scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself. It handles the case in which velocity variations at depth are hidden by near-surface velocity fluctuations. Using an acquisition system that combines an array of sources and an array of receivers, coupled with controlled velocity variations, we tested the ability of beam-forming techniques to track velocity variations separately for body waves and surface waves. After wave separation through double beam forming, the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets. Finally, a method was tested to estimate near-surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth.

Elliptic Airfoil Stall Analysis With Trailing Edge Slots

2010 ◽  
Author(s):  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Lift Coefficient ◽  
Leading Edge ◽  
Surface Velocity ◽  
Circulation Control ◽  
West Virginia University ◽  
Trailing Edge ◽  
Near Surface ◽  
Wind Speeds ◽  
Edge Location ◽  
Stall Angle

Circulation control (CC) is a high-lift methodology that can be used on a variety of aerodynamic applications. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft where the early models were referred to as “blown flaps”. Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a lifting surface This phenomenon keeps the boundary layer jet attached to the wing surface thus increasing the lift generated on the surface. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient. It should be noted that due to the trailing edge location of the circulation control exit jet, a “virtual” camber is created with the free stream air adding length to the overall airfoil. Due to this phenomena, the actual stall angle measured increased from eight degrees on the un-augmented airfoil, to a maximum of twelve degrees.

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