THE SIGNIFICANCE OF DIFFRACTION IN THE INVESTIGATION OF FAULTS

Geophysics ◽  
1952 ◽  
Vol 17 (4) ◽  
pp. 843-858 ◽  
Author(s):  
Theodor Krey
Keyword(s):  
Seismic Reflection ◽  
Seismic Waves ◽  
Sudden Change ◽  
Seismic Profile ◽  
Acute Angle ◽  
Oscillation Pattern ◽  
Reef Edge

Seismic reflection records taken across faults frequently show an overlapping of reflections from the displaced blocks. It is demonstrated that diffraction of seismic waves is a cause and the effect may be used in interpretation. Overlapping is increased if a seismic profile crosses a fault at an acute angle. Plotted dips will be inaccurate unless diffraction is taken into account. Further, the diffraction oscillation pattern will also be obtained if a reflection horizon terminates for a reason other than faulting, for example, at a wedgeout or reef edge, or at a sudden change of facies. The facts developed are demonstrated by practical examples in which attention is directed to the approximations involved in plotting the boundaries of discontinuities.

Crosscoherence-based interferometry for the retrieval of first arrivals and subsequent tomographic imaging of differential weathering

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. Q37-Q48 ◽  
Author(s):  
Joachim Place ◽  
Deyan Draganov ◽  
Alireza Malehmir ◽  
Christopher Juhlin ◽  
Chris Wijns
Keyword(s):  
Seismic Waves ◽  
Seismic Velocity ◽  
Signal To Noise Ratio ◽  
Seismic Profile ◽  
Seismic Interferometry ◽  
Near Surface ◽  
Tomographic Images ◽  
Traveltime Tomography ◽  
Seismic Methods ◽  
Source Signal

Exhumation of crust exposes rocks to weathering agents that weaken the rocks’ mechanical strength. Weakened rocks will have lower seismic velocity than intact rocks and can therefore be mapped using seismic methods. However, if the rocks are heavily weathered, they will attenuate controlled-source seismic waves to such a degree that the recorded wavefield would become dominated by ambient noise and/or surface waves. Therefore, we have examined the structure of differential weathering by first-break traveltime tomography over a seismic profile extending approximately 3.5 km and acquired at a mining site in Zambia using explosive sources and a source based on the swept-impact seismic technique (SIST). Seismic interferometry has been tested for the retrieval of supervirtual first arrivals masked by uncorrelated noise. However, use of crosscorrelation in the retrieval process makes the method vulnerable to changes in the source signal (explosives and SIST). Thus, we have developed a crosscoherence-based seismic-interferometry method to tackle this shortcoming. We investigate the method’s efficiency in retrieving first arrivals and, simultaneously, correctly handling variations in the source signal. Our results illustrate the superiority of the crosscoherence- over crosscorrelation-based method for retrieval of the first arrivals, especially in alleviating spurious ringyness and in terms of the signal-to-noise ratio. These benefits are observable in the greater penetration depth and the improved resolution of the tomography sections. The tomographic images indicate isolated bodies of higher velocities, which may be interpreted as fresh rocks embedded into a heavily weathered regolith, providing a conspicuous example of differential weathering. Our study advances the potential of seismic methods for providing better images of the near surface (the critical zone).

Multiscale seismic imaging of active fault zones for hazard assessment: A case study of the Santa Monica fault zone, Los Angeles, California

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 479-489 ◽  
Author(s):  
Thomas L. Pratt ◽  
James F. Dolan ◽  
Jackson K. Odum ◽  
William J. Stephenson ◽  
Robert A. Williams ◽  
...  
Keyword(s):  
High Resolution ◽  
Los Angeles ◽  
Hazard Assessment ◽  
Seismic Reflection ◽  
Seismic Profile ◽  
Strike Slip ◽  
Alluvial Fan ◽  
Depth Range ◽  
Seismic Reflection Profile ◽  
Santa Monica

High‐resolution seismic reflection profiles at two different scales were acquired across the transpressional Santa Monica Fault of north Los Angeles as part of an integrated hazard assessment of the fault. The seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies. The trench shows a series of near‐vertical strike‐slip faults beneath a topographic scarp inferred to be caused by thrusting on the Santa Monica fault. Analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike‐slip faults within the past 50 000 years, with the latest being 1000 to 3000 years ago. A 3.8-km-long, high‐resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the Santa Monica Fault (upper 300 m) to dip northward between 30° and 55°, most likely 30° to 35°, in contrast to the 60° to 70° dip interpreted for the deeper portion of the fault. Prominent, nearly continuous reflectors on the profile are interpreted to be the erosional unconformity between the 1.2 Ma and older Pico Formation and the base of alluvial fan deposits. The unconformity lies at depths of 30–60 m north of the fault and 110–130 m south of the fault, with about 100 m of vertical displacement (180 m of dip‐slip motion on a 30°–35° dipping fault) across the fault since deposition of the upper Pico Formation. The continuity of the uncomformity on the seismic profile constrains the fault to lie in a relatively narrow (50 m) zone, and to project to the surface beneath Ohio Avenue immediately south of the trench. A very high‐resolution seismic profile adjacent to the trench images reflectors in the 15 to 60 m depth range that are arched slightly by folding just north of the fault. A disrupted zone on the profile beneath the south end of the trench is interpreted as being caused by the deeper portions of the trenched strike‐slip faults where they merge with the thrust fault.

Anisotropic frequency-dependent spreading of seismic waves from first-arrival vertical seismic profile data analysis

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. C41-C52 ◽  
Author(s):  
Amin Baharvand Ahmadi ◽  
Igor Morozov
Keyword(s):  
Seismic Waves ◽  
Seismic Profile ◽  
Anisotropic Scattering ◽  
Profile Data ◽  
Vertical Seismic Profile ◽  
Data Set ◽  
Frequency Dependent ◽  
Geometric Spreading ◽  
First Arrival ◽  
Viscoelastic Modeling

A model of first-arrival amplitude decay combining geometric spreading, scattering, and inelastic dissipation is derived from a multioffset, 3D vertical seismic profile data set. Unlike the traditional approaches, the model is formulated in terms of path integrals over the rays and without relying on the quality factor ([Formula: see text]) for rocks. The inversion reveals variations of geometric attenuation (wavefront curvatures and scattering, [Formula: see text]) and the effective attenuation parameter ([Formula: see text]) with depth. Both of these properties are also found to be anisotropic. Scattering and geometric spreading (focusing and defocusing) significantly affect seismic amplitudes at lower frequencies and shallower depths. Statistical analysis of model uncertainties quantitatively measures the significance of these results. The model correctly predicts the observed frequency-dependent first-arrival amplitudes at all frequencies. This and similar models can be applied to other types of waves and should be useful for true-amplitude studies, including inversion, inverse [Formula: see text]-filtering, and amplitude variations with offset analysis. With further development of petrophysical models of internal friction and elastic scattering, attenuation parameters [Formula: see text] and [Formula: see text] should lead to constraints on local heterogeneity and intrinsic physical properties of the rock. These parameters can also be used to build models of the traditional frequency-dependent [Formula: see text] for forward and inverse numerical viscoelastic modeling.

What can deep seismic reflection data tell us about hydrocarbon prospectivity in onshore

2009 ◽  
Vol 49 (2) ◽  
pp. 598
Author(s):  
Thomas Bernecker ◽  
Jenny Maher
Keyword(s):  
Seismic Reflection ◽  
Oil And Gas ◽  
Sedimentary Basins ◽  
Seismic Profile ◽  
Significant Loss ◽  
Coarse Grained ◽  
Seismic Reflection Data ◽  
Deep Seismic Reflection ◽  
Structural Style ◽  
Basin Fill

Now in its third year, Geoscience Australia’s Onshore Energy Security Program has acquired several suites of regional geological and geophysical data. The data includes several deep seismic reflection surveys that have been designed to image: basement provinces with high geothermal gradients that may contain uranium enrichments and are potential candidates for geothermal energy; geological terrane boundaries; and, sedimentary basins that are known to host petroleum system elements but are under-explored. Seismic signals are recorded down to 20 seconds two-way-time (TWT) which corresponds to 25–35 km depth depending on dominant lithologies. Basinal sections normally extend down to 6–8 sec TWT and the data is of such high quality that any section of the seismic profile can be enlarged without significant loss of resolution. Deep reflection surveys are able to image the relationship between crystalline basement and overlying basin sequences very clearly and also allow interpretations of structural styles as well as impacts of deformational processes on the basin-fill. A new basinal section was discovered beneath the Eromanga Basin suite of sediments. Named the Mullangera Basin,its structural style and basement relationship seem to indicate some affinity with the Georgina Basin, located further west. The succession is clearly composed of several sequences that contain both fine and coarse-grained sediments. If a geological relationship with the Georgina Basin can be ascertained, a new hydrocarbon prospective area could be delineated. Another new section was discovered beneath the Devonian section of the Darling Basin. Judging by the fast acoustic velocities, the entire basin-fill sequence appears to be very dense and therefore largely non-porous and of low permeability. While low poro-perm characteristics would normally be translated to low prospectivity for oil and gas, the potential for unconventional hydrocarbons such a tight-gas and shale-gas warrants further attention.

PROCESSING OF SEISMIC DIFFRACTIONS FROM CARBONATE NODULES IN CLAY FORMATIONS

Geophysics ◽  
2021 ◽  
pp. 1-64
Author(s):  
Cinzia Bellezza ◽  
Flavio Poletto ◽  
Biancamaria Farina ◽  
Giorgia Pinna ◽  
Laurent Wouters ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Reflection ◽  
Synthetic Data ◽  
Seismic Profile ◽  
Radioactive Waste Disposal ◽  
Small Scale ◽  
Boom Clay ◽  
Seismic Image ◽  
Imaging Results ◽  
Clay Formation

The problem of localizing small (relative to wavelength) scatterers by diffractions to enhance their use in identifying small-scale details in a seismic image is extremely important in shallow exploration, to identify interesting features such as fractures, caves and faults. The conventional approach based on seismic reflection is limited in resolution by the Rayleigh criterion. In certain acquisition geometries, such as crosswell surveys aimed at obtaining high resolution signals, the availability of suitable datasets for effective migration depends on the spatial extent of the available source and receiver data intervals. With the aim of overcoming the resolution limits of seismic reflection, we studied the detectability, response, and location of meter- and possibly sub-meter-dimension carbonate concretions (septaria) in the Boom Clay Formation (potential host rocks for radioactive waste disposal) by diffraction analysis of high-frequency signals. We investigated diffraction wavefields by signal separation, focusing, and high-resolution coherency analysis using the MUltiple Signal Classification (MUSIC) method and semblance. The investigation was performed for two different surveys in Belgium, a shallow and high resolution Reverse Vertical Seismic Profile (RVSP) and a near-offset crosswell application at Kruibeke and ON-MOL-2 sites, respectively. The data analysis is supported by synthetic wavefield modeling. The multi-offset RVSP provides the appropriate geometry to observe and investigate the septaria diffractions both from depth and the surface. The crosswell approach, calibrated using synthetic data in the analysis of wavefield patterns in 2D, shows promising imaging results with field data of a selected diffraction zone in the interwell area.

The multi-2D seismic imaging of the Solfatara Volcano, Italy, inferred by seismic attributes.

2020 ◽  
Author(s):  
Sergio Gammaldi ◽  
Amir Ismail ◽  
Teresa Chiuso ◽  
Aldo Zollo
Keyword(s):  
Seismic Reflection ◽  
Velocity Model ◽  
Seismic Profile ◽  
Seismic Attributes ◽  
Campi Flegrei ◽  
Frequency Noise ◽  
Geophysical Investigation ◽  
Seismic Reflection Data ◽  
Migration Pathways ◽  
Solfatara Crater

<p>The imaging of seismic reflection data provides a powerful high-resolution method for studying volcano structure and fluids presence. The shallow structure of the Solfatara crater, a surface marker of deep magmatic activity inside Campi Flegrei caldera (Southern Italy), is characterized in terms of seismic profile and attributes. The main contribution of this work is to provide a detailed and improved seismic reflection image of the Solfatara crater and the identification of gas accumulation. The profiles are deployed along the NNE-SSW directions, the first, and the second orthogonal to the last. The two profiles are 400 m long acquired during the active experiment RICEN (Repeated Induced Earthquake and Noise) performed in the framework of the EU project MEDSUV between May and November 2014. Pre-stack processing of the seismic data has been performed in order to remove the noisy traces, low-frequency noise and reduce the ground roll phases. A very detailed velocity analysis for the NMO correction has been performed with the integration of information derived from the Vp velocity model previously obtained by the non-linear Bayesian technique. After having applied residual statics and DMO corrections, the CMP gathering, the post-stack Kirchhoff migration technique was performed to produce the final seismic profiles in time and depth. Once having obtained the post-stack migrated imaged, the energy, root mean square, envelope and sweetness attributes were computed for defining the maximum and minimum value of amplitude zones. In addition, other attributes as the time-gain attribute in order to interpret the deep reflectors and the variance attribute to define the faults, discontinuities, and chaotic zones have been evaluated. To enhance fluids identification the Amplitude Versus Offset (AVO) variation technique has been further applied to identify the gas zone in the explored sections. By integrating all information from the original seismic profile, seismic attributes and geophysical investigation relative to the Solfatara volcano, the multi-2D image presents the fluids trapped in the Solfatara crater at depths between 10 to 50 m below the surface of the crater and their migration pathways up to 150 meters depth.</p>

Offset‐amplitude variation and controlled‐amplitude processing

Geophysics ◽  
1985 ◽  
Vol 50 (12) ◽  
pp. 2697-2708 ◽  
Author(s):  
Gary Yu
Keyword(s):  
Seismic Waves ◽  
Gulf Coast ◽  
Seismic Profile ◽  
Angle Of Incidence ◽  
Elastic Parameters ◽  
Amplitude Analysis ◽  
Coherent Noise ◽  
Seismic Amplitude ◽  
Amplitude Data ◽  
Amplitude Anomaly

The partition of plane seismic waves at plane interfaces introduces changes in seismic amplitude which vary with angle of incidence. These amplitude variations are a function of the elastic parameters of rocks on either side of the interface. Controlled‐amplitude processing is designed to obtain the true amplitude information which is geologic in origin. The offset‐amplitude information may be successfully used to predict the fluid type in reservoir sands. Various tests were carried out on a seismic profile from the Gulf Coast. The processing comparison emphasized the effects and pitfalls of trace equalization, coherent noise, offset, and surface‐related problems. Two wells drilled at amplitude anomaly locations confirmed the prediction of hydrocarbons from offset‐amplitude analysis. Furthermore, controlled‐amplitude processing provided clues in evaluating reservoir quality, which was not evident on the conventional relative amplitude data.

Analysis and application of coal-seam seismic waves for detecting abandoned mines

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. M7-M15 ◽  
Author(s):  
Daniel J. Yancey ◽  
Matthias G. Imhof ◽  
John E. Feddock ◽  
Tod Gresham
Keyword(s):  
Coal Seam ◽  
Seismic Reflection ◽  
Seismic Waves ◽  
Underground Mine ◽  
Abandoned Mines ◽  
Abandoned Mine ◽  
Reflection Data ◽  
Seismic Methods ◽  
Mine Voids ◽  
Transmission And Reflection

Two in-seam reflection surveys and one transmission survey were acquired at an abandoned underground mine near Hurley, Virginia, to demonstrate the feasibility of detecting abandoned-mine voids utilizing coal-seam seismic waves. Standard, commonly available tools for seismic reflection processing were used. The mine was detected and located by using trapped coal-seam seismic waves observed in both the transmission and reflection data. Detecting the void, however, was not good enough to replace drilling entirely. We conclude that in-seam seismic methods can be used for detection; but if a potential void is detected, focused drilling should be applied for accurate mapping and to circumvent potentially hazardous areas.

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