Migration of shallow seismic reflection data

Geophysics ◽  
1994 ◽  
Vol 59 (3) ◽  
pp. 402-410 ◽  
Author(s):  
Ross A. Black ◽  
Don W. Steeples ◽  
Richard D. Miller
Keyword(s):  
Seismic Reflection ◽  
Large Data ◽  
Flow Chart ◽  
Seismic Section ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Simple Set

We present an analysis of migration effects on seismic reflection images of very shallow targets such as those that are common objectives of engineering, groundwater, and environmental investigations. We use an example of seismic reflection data from depths of 5 to 15 m that show negligible effect from migration, despite the apparent steep dip on the seismic section. Our analysis of the question of when to migrate shallow reflection data indicates it is critical to take into account the highly variable near‐surface velocities and the vertical exaggeration on the seismic section. A simple set of calculations is developed as well as a flow chart based on the “migrator’s equation” that can predict whether migration of an arbitrary shallow seismic section is advisable. Because shallow reflection data are often processed on personal computers, unnecessary migration of a large data set can be prohibitively time‐consuming and wasteful.

Shallow seismic reflection study of a glaciated valley

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1395-1407 ◽  
Author(s):  
Frank Büker ◽  
Alan G. Green ◽  
Heinrich Horstmeyer
Keyword(s):  
Seismic Reflection ◽  
High Amplitude ◽  
Data Sets ◽  
Seismic Section ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Northern Switzerland ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Glaciated Valley

Shallow seismic reflection data were recorded along two long (>1.6 km) intersecting profiles in the glaciated Suhre Valley of northern Switzerland. Appropriate choice of source and receiver parameters resulted in a high‐fold (36–48) data set with common midpoints every 1.25 m. As for many shallow seismic reflection data sets, upper portions of the shot gathers were contaminated with high‐amplitude, source‐generated noise (e.g., direct, refracted, guided, surface, and airwaves). Spectral balancing was effective in significantly increasing the strength of the reflected signals relative to the source‐generated noise, and application of carefully selected top mutes ensured guided phases were not misprocessed and misinterpreted as reflections. Resultant processed sections were characterized by distributions of distinct seismic reflection patterns or facies that were bounded by quasi‐continuous reflection zones. The uppermost reflection zone at 20 to 50 ms (∼15 to ∼40 m depth) originated from a boundary between glaciolacustrine clays/silts and underlying glacial sands/gravels (till) deposits. Of particular importance was the discovery that the deepest part of the valley floor appeared on the seismic section at traveltimes >180 ms (∼200 m), approximately twice as deep as expected. Constrained by information from boreholes adjacent to the profiles, the various seismic units were interpreted in terms of unconsolidated glacial, glaciofluvial, and glaciolacustrine sediments deposited during two principal phases of glaciation (Riss at >100 000 and Würm at ∼18 000 years before present).

An example of extreme near-surface variability in shallow seismic reflection data

2016 ◽  
Vol 4 (3) ◽  
pp. SH1-SH9
Author(s):  
Steven D. Sloan ◽  
J. Tyler Schwenk ◽  
Robert H. Stevens
Keyword(s):  
Seismic Reflection ◽  
Field Data ◽  
Low Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Low Velocity Layer ◽  
Velocity Layer

Variability of material properties in the shallow subsurface presents challenges for near-surface geophysical methods and exploration-scale applications. As the depth of investigation decreases, denser sampling is required, especially of the near offsets, to accurately characterize the shallow subsurface. We have developed a field data example using high-resolution shallow seismic reflection data to demonstrate how quickly near-surface properties can change over short distances and the effects on field data and processed sections. The addition of a relatively thin, 20 cm thick, low-velocity layer can lead to masked reflections and an inability to map shallow reflectors. Short receiver intervals, on the order of 10 cm, were necessary to identify the cause of the diminished data quality and would have gone unknown using larger, more conventional station spacing. Combined analysis of first arrivals, surface waves, and reflections aided in determining the effects and extent of a low-velocity layer that inhibited the identification and constructive stacking of the reflection from a shallow water table using normal-moveout-based processing methods. Our results also highlight the benefits of using unprocessed gathers to pragmatically guide processing and interpretation of seismic data.

scholarly journals Using Seismic Attributes in seismotectonic research: an application to the Norcia's Mw = 6.5 earthquake (30th October 2016) in Central Italy

2019 ◽  
Author(s):  
Maurizio Ercoli ◽  
Emanuele Forte ◽  
Massimiliano Porreca ◽  
Ramon Carbonell ◽  
Cristina Pauselli ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Central Italy ◽  
Seismic Attributes ◽  
Seismic Attribute ◽  
Data Set ◽  
Epicentral Zone ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Attribute Analysis

Abstract. In seismotectonic studies, seismic reflection data are a powerful tool to unravel the complex deep architecture of active faults. Such tectonic structures are usually mapped at surface through traditional geological surveying whilst seismic reflection data may help to trace their continuation from the near-surface down to hypocentral depth. In this study, we propose the application of the seismic attributes technique, commonly used in seismic reflection exploration by oil industry, to seismotectonic research for the first time. The study area is a geologically complex region of Central Italy, recently struck by a long-lasting seismic sequence including a Mw 6.5 main-shock. A seismic reflection data-set consisting of three vintage seismic profiles, currently the only available across the epicentral zone, constitutes a singular opportunity to attempt a seismic attribute analysis. This analysis resulted in peculiar seismic signatures which generally correlate with the exposed surface geologic features, and also confirming the presence of other debated structures. These results are critical, because provide information also on the relatively deep structural setting, mapping a prominent, high amplitude regional reflector that marks the top basement, interpreted as important rheological boundary. Complex patterns of high-angle discontinuities crossing the reflectors have been also identified. These dipping fabrics are interpreted as the expression of fault zones, belonging to the active normal fault systems responsible for the seismicity of the region. This work demonstrates that seismic attribute analysis, even if used on low-quality vintage 2D data, may contribute to improve the subsurface geological interpretation of areas characterized by high seismic potential.

scholarly journals Time-lapse imaging using 3D ultra-high-frequency marine seismic reflection data

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. P13-P25
Author(s):  
Michael J. Faggetter ◽  
Mark E. Vardy ◽  
Justin K. Dix ◽  
Jonathan M. Bull ◽  
Timothy J. Henstock
Keyword(s):  
High Frequency ◽  
Seismic Reflection ◽  
High Tide ◽  
Time Lapse ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Ultra High Frequency ◽  
Reflection Data ◽  
Marine Seismic

Time-lapse (4D) seismic imaging is now widely used as a tool to map and interpret changes in deep reservoirs as well as investigate dynamic, shallow hydrological processes in the near surface. However, there are very few examples of time-lapse analysis using ultra-high-frequency (UHF; kHz range) marine seismic reflection data. Exacting requirements for navigation can be prohibitive for acquiring coherent, true-3D volumes. Variable environmental noise can also lead to poor amplitude repeatability and make it difficult to identify differences that are related to real physical changes. Overcoming these challenges opens up a range of potential applications for monitoring the subsurface at decimetric resolution, including geohazards, geologic structures, as well as the bed-level and subsurface response to anthropogenic activities. Navigation postprocessing was incorporated to improve the acquisition and processing workflow for the 3D Chirp subbottom profiler and provide stable, centimeter-level absolute positioning, resulting in well-matched 3D data and mitigating 4D noise for data stacked into [Formula: see text] common-midpoint bins. Within an example 4D data set acquired on the south coast of the UK, interpretable differences are recorded within a shallow gas blanket. Reflections from the top and bottom of a gas pocket are imaged at low tide, whereas at high tide only the upper reflection is imaged. This case study demonstrates the viability of time-lapse UHF 3D seismic reflection for quantitative mapping of decimeter-scale changes within the shallow marine subsurface.

Reducing source‐generated noise in shallow seismic data using linear and hyperbolic τ‐p transformations

Geophysics ◽  
2001 ◽  
Vol 66 (5) ◽  
pp. 1612-1621 ◽  
Author(s):  
Roman Spitzer ◽  
Frank O. Nitsche ◽  
Alan G. Green
Keyword(s):  
Seismic Reflection ◽  
Guided Waves ◽  
Relative Strength ◽  
Data Set ◽  
Processing Scheme ◽  
Seismic Reflection Data ◽  
Northern Switzerland ◽  
Reflection Data ◽  
Shallow Seismic ◽  
P Domain

High‐resolution seismic reflection data recorded at many locations on the earth are plagued by the overwhelming effects of direct, refracted, guided, and surface waves. These different components of source‐generated noise may completely mask reflections at traveltimes <∼50–100 ms. Conventional processing methods that include the time‐consuming application of mute functions may lead to the misprocessing of source‐generated noise (especially guided waves) as reflected events and/or the unintentional removal of important shallow reflections. We introduce a combined linear and hyperbolic τ‐p processing scheme that results in the effective separation of reflections from source‐generated noise. After applying linear moveout terms that adjust the direct, refracted, and guided arrivals to appear horizontal to subhorizontal, the reduced traveltime shot gathers are transformed into the linear τ‐p domain. It is then straightforward to design a single τ‐p filter that eliminates most of the source‐generated noise throughout the entire data set. Following inverse linear τ‐p transformation and removal of the linear moveout terms, the filtered shot gathers contain reflections and residual elements of the source‐generated noise. Because summing along hyperbolas favors reflections, transforming the filtered shot gathers into the hyperbolic τ‐p domain leads to significant enhancements in the S/N ratio. A simple rescaling of data values in the hyperbolic τ‐p domain, which results in the loss of true amplitude information, increases further the relative strength of the reflected signals. Finally, inverse hyperbolic transformation yields shot gathers dominated by reflections. In tests of the combined τ‐p processing scheme on a synthetic shot gather and on a complete shallow seismic reflection data set recorded in northern Switzerland, significant improvements in the quality of reflections in the prestacked data and on a fully processed section are readily apparent. According to the results of these tests, the new scheme works well for reflections originating from flat and dipping horizons.

Shallow 3-D seismic reflection surveying: Data acquisition and preliminary processing strategies

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1434-1450 ◽  
Author(s):  
Frank Büker ◽  
Alan G. Green ◽  
Heinrich Horstmeyer
Keyword(s):  
Data Acquisition ◽  
Seismic Reflection ◽  
Full Range ◽  
Depth Range ◽  
Data Set ◽  
Processing Scheme ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Glacial Sediments ◽  
Reflection Data

A comprehensive strategy of 3-D seismic reflection data acquisition and processing has been used in a study of glacial sediments deposited within a Swiss mountain valley. Seismic data generated by a downhole shotgun source were recorded with single 30-Hz geophones distributed at 3 m × 3 m intervals across a 357 m × 432 m area. For most common‐midpoint (CMP) bins, traces covering a full range of azimuths and source‐receiver distances of ∼2 to ∼125 m were recorded. A common processing scheme was applied to the entire data set and to various subsets designed to simulate data volumes collected with lower density source and receiver patterns. Comparisons of seismic sections extracted from the processed 3-D subsets demonstrated that high‐fold (>40) and densely spaced (CMP bin sizes ⩽ 3 m × 3 m) data with relatively large numbers (>6) of traces recorded at short (<20 m) source‐receiver offsets were essential for obtaining clear images of the shallowest (<100 ms) reflecting horizons. Reflections rich in frequencies >100 Hz at traveltimes of ∼20 to ∼170 ms provided a vertical resolution of 3 to 6 m over a depth range of ∼15 to ∼150 m. The shallowest prominent reflection at 20 to 35 ms (∼15 to 27 m depth) originated from the boundary between a near‐surface sequence of clays/silts and an underlying unit of heterogeneous sands/gravels.

Large near‐surface velocity gradients on shallow seismic reflection data

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1348-1356 ◽  
Author(s):  
Richard D. Miller ◽  
Jianghai Xia
Keyword(s):  
Seismic Reflection ◽  
Surface Velocity ◽  
Coherent Noise ◽  
Lower Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Velocity Gradients ◽  
Large Velocity

Extreme velocity gradients occasionally present within near‐surface materials can inhibit optimal common midpoint (CMP) stacking of near‐surface reflection arrivals. For example, abrupt increases in velocity are observed routinely at the bedrock surface and at the boundary between the vadose and the saturated zone. When a rapid increase in near‐surface velocity is found, NMO correction artifacts manifested on CMP gathers as sample reversion, sample compression, or duplication of reflection wavelets can reduce S/N ratio on stacked data or can stack coherently. Elimination of these nonstretch‐related artifacts using conventional NMO-stretch muting requires near‐vertically incident reflection arrivals and allowable stretch ratios as small as 5% in some shallow environments. Radical allowable stretch mutes are not a feasible means to subdue these artifacts if high‐amplitude coherent noise on near‐offset traces inhibits identification and digital enhancement of shallow reflections. On most shallow seismic reflection data, long‐offset reflection arrivals (but less than wide angle) are critical to the generation of an interpretable stacked section. The difference in offset between the optimum window for shallow reflections within unsaturated sediments and reflections from the underlying saturated or consolidated‐material portion of the section inherently limits the effectiveness of conventional NMO corrections. Near‐surface average velocity increases of 200% in less than two wavelengths and at two‐way traveltimes less than 60 ms are not uncommon on shallow reflection data. Near‐surface reflections separated by large velocity gradients can rarely be accurately or optimally CMP processed using conventional approaches to NMO corrections. Large velocity‐gradient shallow reflection data require segregation of shallow lower velocity reflections from higher velocity reflections during processing to maximize the accuracy and resolution potential of the stacked section, as shown by examples herein.

An example of the effects of near-surface variability on shallow seismic reflection data

2015 ◽  
Author(s):  
Steven D. Sloan* ◽  
Matt Ralston ◽  
Robert H. Stevens ◽  
J. Tyler Schwenk
Keyword(s):  
Seismic Reflection ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Surface Variability

scholarly journals Mapping a bedrock surface under dry alluvium with shallow seismic reflections

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1528-1534 ◽  
Author(s):  
Richard D. Miller ◽  
Don W. Steeples ◽  
Michael Brannan
Keyword(s):  
Seismic Reflection ◽  
Dominant Frequency ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Analog To Digital ◽  
Evaporation Pond ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Analog To Digital Conversion ◽  
Alluvial Material

Shallow seismic‐reflection techniques were used to image the bedrock‐alluvial interface, near a chemical evaporation pond in the Texas Panhandle, allowing optimum placement of water‐quality monitor wells. The seismic data showed bedrock valleys as shallow as 4 m and accurate to within 1 m horizontally and vertically. The normal‐moveout velocity within the near‐surface alluvium varies from 225 m/s to 400 m/s. All monitor‐well borings near the evaporation pond penetrated unsaturated alluvial material. On most of the data, the wavelet reflected from the bedrock‐alluvium interface has a dominant frequency of around 170 Hz. Low‐cut filtering at 24 dB/octave below 220 Hz prior to analog‐to‐digital conversion enhanced the amplitude of the desired bedrock reflection relative to the amplitude of the unwanted ground roll. The final bedrock contour map derived from drilling and seismic‐reflection data possesses improved resolution and shows a bedrock valley not interpretable from drill data alone.

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