OBSERVED REFLECTION AND DIFFRACTION WAVELET COMPLEXES IN TWO‐DIMENSIONAL SEISMIC MODEL STUDIES OF SIMPLE FAULTS

Geophysics ◽  
1965 ◽  
Vol 30 (1) ◽  
pp. 72-86 ◽  
Author(s):  
Delbert Ray Harper
Keyword(s):  
Fault Plane ◽  
Two Dimensional ◽  
Seismic Model ◽  
Transmitted Pulse ◽  
Model Studies ◽  
Seismic Models

The ultrasonic reflection‐diffraction complexes from simple rectangular configurations are compared for various two‐dimensional seismic models. These models represent simple faults and faults with sharp folds for two‐ and three‐layer cases. In particular, the model with cavity and models with extrusions (with square corners) represent simple faults in two‐ and three‐layer cases, respectively. Similarly the model with cavity and models with recesses (with curved corners) correspond to a sharp fold in the vicinity of the fault in two‐ and three‐layer cases. Masking of the fault plane by overlapping of diffraction upon reflection events is shown to be much more prominent for the simple fault with sharp fold than for a simple fault in both the two‐ and three‐layer cases. For the three‐layer cases, models employing recesses and extrusions have vertical dimensions less than the wavelength of the transmitted pulse; hence, waveforms for these models are more complicated due to composition of wavelets from the first interface with those from the second interface. Differences between the models were explained by synthetic waveforms derived using superposition of diffraction wavelets for the two‐layer cases (cavity models), and overlapping wavelets for the three‐layer cases (models with recesses and extrusions).

GRAVITY ANOMALIES OF TWO‐DIMENSIONAL FAULTS

Geophysics ◽  
1966 ◽  
Vol 31 (2) ◽  
pp. 372-397 ◽  
Author(s):  
L. P. Geldart ◽  
Denis E. Gill ◽  
Bijon Sharma
Keyword(s):  
Fault Plane ◽  
Marked Effect ◽  
Gravity Anomalies ◽  
Two Dimensional ◽  
Gravity Effect ◽  
Fault Density ◽  
Wide Range ◽  
Bed Thickness ◽  
Two Sides ◽  
Simplified Formula

A simplified formula is given for the gravity effect of a horizontal semi‐infinite block truncated by a dipping plane. This formula is used to obtain curves illustrating the gravity anomalies for blocks having different thicknesses and depths truncated by planes dipping at various angles. By combining two blocks, results are obtained for faulted horizontal beds for a wide range of bed thicknesses and depths, fault displacements and dips. These should be useful as guides in interpreting fault anomalies, and in planning gravity programs intended to map faults. The most striking feature of the curves is the marked effect of the dip of the fault plane on the curves for faulted beds. The asymmetry of the fault curves is related mainly to the dip and can be used to determine dips between 30 and 90 degrees. If the dip of the fault, density contrast, and bed thickness are known, the depths to the bed on the two sides of the fault are given by the sizes and positions of the gravity maximum and minimum.

Ultrasonic Imaging for the Seismic Model Fault Plane

1989 ◽  
pp. 715-722
Author(s):  
Yuan Yi-Quan ◽  
Yin Ging-Rui ◽  
Shi Bing-Wen ◽  
Shen Shou-Peng
Keyword(s):  
Fault Plane ◽  
Ultrasonic Imaging ◽  
Seismic Model

Stratal slicing, Part I: Realistic 3-D seismic model

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 502-513 ◽  
Author(s):  
Hongliu Zeng ◽  
Milo M. Backus ◽  
Kenneth T. Barrow ◽  
Noel Tyler
Keyword(s):  
Seismic Data ◽  
Seismic Event ◽  
Necessary Condition ◽  
Single Event ◽  
Seismic Model ◽  
Geological Time ◽  
Depositional Facies ◽  
Impedance Boundary ◽  
Depositional Units ◽  
Seismic Models

Two‐dimensional, fenced 2-D, and 3-D isosurface displays of some realistic 3-D seismic models built in the lower Miocene Powderhorn Field, Calhoun County, Texas, demonstrate that a seismic event does not necessarily follow an impedance boundary defined by a geological time surface. Instead, the position of a filtered impedance boundary relative to the geological time surface may vary with seismic frequency because of inadequate resolution of seismic data and to the en echelon or ramp arrangement of impedance anomalies of sandstone. Except for some relatively time‐parallel seismic events, the correlation error of event picking is large enough to distort or even miss the majority of the target zone on stratal slices. In some cases, reflections from sandstone bodies in different depositional units interfere to form a single event and, in one instance, an event tying as many as six depositional units (interbedded sandy and shaly layers) over 50 m was observed. Frequency independence is a necessary condition for selecting time‐parallel reference events. Instead of event picking, phantom mapping between such reference events is a better technique for picking stratal slices, making it possible to map detailed depositional facies within reservoir sequences routinely and reliably from 3-D seismic data.

SEISMIC MODEL EXPERIMENTS WITH SHEAR WAVES

Geophysics ◽  
1959 ◽  
Vol 24 (1) ◽  
pp. 40-48 ◽  
Author(s):  
J. F. Evans
Keyword(s):  
Field Experiments ◽  
Shear Waves ◽  
High Amplitude ◽  
Homogeneous Layer ◽  
Small Scale ◽  
Seismic Model ◽  
Low Velocity ◽  
Model Experiments ◽  
Velocity Surface ◽  
Seismic Models

The experimental study of shear waves in the earth has been limited by the difficulty of producing them in sufficient strength. However, sensitive piezoelectric shear plates can now be made which enable experimentation with shear waves using small‐scale seismic models. Seismic model experiments serve to demonstrate the simplicity of SH‐shear wave reflections in a single homogeneous layer, the production of SH waves by an impulsive horizontal thrust, and the development of relatively high amplitude Love waves in a low‐velocity surface layer. The results of these model experiments with shear waves are in general agreement with and confirm theory. They also agree with the results of field experiments in the scattered cases for which comparison is available.

THREE‐DIMENSIONAL SEISMIC MODEL STUDIES

Geophysics ◽  
1955 ◽  
Vol 20 (1) ◽  
pp. 19-32 ◽  
Author(s):  
F. K. Levin ◽  
H. C. Hibbard
Keyword(s):  
Wave Propagation ◽  
Surface Wave ◽  
Elastic Wave ◽  
Surface Waves ◽  
Shear Waves ◽  
Three Dimensional ◽  
Seismic Model ◽  
Model Studies ◽  
Ground Roll ◽  
Detector Configurations

Elastic wave propagation in a two‐layer section has been studied with a solid two‐bed model and records resembling seismograms obtained for the four possible source‐detector configurations. Numerous events are identified. Among these, the shear waves are found to be surprisingly prominent. The amplitude of the ground roll falls off approximately as [Formula: see text] This is the amplitude‐range dependence expected for a surface wave. The ability of two in‐line detectors to reduce surface waves has been demonstrated.

Seismic model studies of the overburden‐bedrock reflection

Geophysics ◽  
1985 ◽  
Vol 50 (11) ◽  
pp. 1684-1688 ◽  
Author(s):  
S. E. Pullan ◽  
J. A. Hunter
Keyword(s):  
Elastic Properties ◽  
Seismic Waves ◽  
Angle Of Incidence ◽  
Seismic Model ◽  
Zoeppritz Equations ◽  
Model Studies ◽  
Seismic Wavelet ◽  
The Earth ◽  
Subsurface Layers ◽  
Phase Variations

One aspect of the modification of seismic waves on passage through the Earth is the partitioning of energy at subsurface interfaces as described by the Zoeppritz equations. These equations have been applied to simple two‐ and three‐layer models to determine the variations in the amplitude and phase of a reflection signal at nonnormal angles of incidence. Synthetic seismograms have been produced to illustrate the effect of these variations on a seismic wavelet. It is found that the phase variations can lead to substantial changes in the character of the reflected wavelet as the source‐geophone distance increases. These changes are dependent on the angle of incidence and on the elastic properties of the subsurface layers. In particular, for models approximating an overburden over bedrock situation, the reflected pulse is predicted to “change phase” when the velocity contrast between the two layers is relatively small. This effect has been observed on field records. Geophysicists should be aware of this phenomenon, both in terms of the problems it may cause in observing a bedrock reflection and in terms of the potential it has for indicating subsurface elastic properties.

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