scholarly journals Static corrections from shallow‐reflection surveys

Geophysics ◽  
1990 ◽  
Vol 55 (6) ◽  
pp. 769-775 ◽  
Author(s):  
D. W. Steeples ◽  
R. D. Miller ◽  
R. A. Black
Keyword(s):  
Layer Thickness ◽  
Seismic Reflection ◽  
P Wave ◽  
Thickness Variation ◽  
Near Surface ◽  
Weathered Zone ◽  
Reflection Data ◽  
Weathered Layer ◽  
Static Corrections ◽  
Thickness Variations

Shallow seismic reflection surveys can assist in determination of velocity and/or thickness variations in near‐surface layers. Static corrections to seismic reflection data compensate for velocity and thickness variations within the “weathered zone.” An uncompensated weathered‐layer thickness variation on the order of 1 m across the length of a geophone array can distort the spectrum of the signal and result in aberrations on final stacked data. P-wave velocities in areas where the weathered zone is composed of unconsolidated materials can be substantially less than the velocity of sound in air. Weathered‐layer thickness variation of 1 m in these low‐velocity materials could result in a static anomaly in excess of 3 ms. Shallow‐reflection data from the Texas panhandle illustrate a real geologic situation with sufficient variability in the near surface to significantly affect seismic signal reflected from depths commonly targeted by conventional reflection surveys. Synthetic data approximating a conventional reflection survey combined with a weathered‐layer model generated from shallow‐reflection data show the possible dramatic static effects of alluvium. Shallow high‐resolution reflection surveys can be used both to determine the severity of intra‐array statics and to assist in the design of a filter to remove much of the distortion such statics cause on deeper reflection data. The static effects of unconsolidated materials can be even more dramatic on S-wave reflection surveys than on comparable P-wave surveys.

Near‐surface seismic reflection profiling of the Matanuska Glacier, Alaska

Geophysics ◽  
2003 ◽  
Vol 68 (1) ◽  
pp. 147-156 ◽  
Author(s):  
Gregory S. Baker ◽  
Jeffrey C. Strasser ◽  
Edward B. Evenson ◽  
Daniel E. Lawson ◽  
Kendra Pyke ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Reflection ◽  
Longitudinal Axis ◽  
Horizontal Distribution ◽  
P Wave ◽  
Near Surface ◽  
Surface Reflection ◽  
Reflection Data ◽  
Basal Ice ◽  
Matanuska Glacier

Several common‐midpoint seismic reflection profiles collected on the Matanuska Glacier, Alaska, clearly demonstrate the feasibility of collecting high‐quality, high‐resolution near‐surface reflection data on a temperate glacier. The results indicate that high‐resolution seismic reflection can be used to accurately determine the thickness and horizontal distribution of debris‐rich ice at the base of the glacier. The basal ice thickens about 30% over a 300‐m distance as the glacier flows out of an overdeepening. The reflection events ranged from 80‐ to 140‐m depth along the longitudinal axis of the glacier. The dominant reflection is from the contact between clean, englacial ice and the underlying debris‐rich basal ice, but a strong characteristic reflection is also observed from the base of the debris‐rich ice (bottom of the glacier). The P‐wave propagation velocity at the surface and throughout the englacial ice is 3600 m/s, and the frequency content of the reflections is in excess of 800 Hz. Supporting drilling data indicate that depth estimates are correct to within ± 1 m.

Near-surface glaciotectonic structures in the sediments of an overdeepened glacial valley revealed by a shallow 3D seismic survey

2021 ◽  
Author(s):  
David Tanner ◽  
Hermann Buness ◽  
Thomas Burschil
Keyword(s):  
Seismic Reflection ◽  
P Wave ◽  
Seismic Survey ◽  
Small Scale ◽  
Academic Press ◽  
Near Surface ◽  
Glacial Sediments ◽  
Area Source ◽  
Terminal Moraine ◽  
Rhine Valley

<p>Glaciotectonic structures commonly include thrusting and folding, often as multiphase deformation. Here we present the results of a small-scale 3-D P-wave seismic reflection survey of glacial sediments within an overdeepened glacial valley in which we recognise unusual folding structures in front of push-moraine. The study area is in the Tannwald Basin, in southern Germany, about 50 km north of Lake Constance, where the basin is part of the glacial overdeepened Rhine Valley. The basin was excavated out of Tertiary Molasse sediments during the Hosskirchian stage, and infilled by 200 m of Hosskirchian and Rissian glacioclastics (Dietmanns Fm.). After an unconformity in the Rissian, a ca. 7 m-thick till (matrix-supported diamicton) was deposited, followed by up to 30 m of Rissian/Würmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last Würmian glaciation overlies these deposits to the SW, not 200 m away.</p><p>We conducted a 3-D, 120 x 120 m², P-wave seismic reflection survey around a prospective borehole site in the study area. Source/receiver points and lines were spaced at 3 m and 9 m, respectively. A 10 s sweep of 20-200 Hz was excited by a small electrodynamic, wheelbarrow-borne vibrator twice at every of the 1004 realized shot positions. We recognised that the top layer of coarse gravel above the till is folded, but not in the conventional buckling sense, rather as cuspate-lobate folding. The fold axes are parallel to the terminal moraine front. The wavelength of the folding varies between 40 and 80 m, and the thickness of the folded layer is on average about 20 m. Cuspate-lobate folding is typical for deformation of layers of differing mechanical competence (after Ramsay and Huber 1987; µ<sub>1</sub>/µ<sub>2</sub> less than 10), so this tell us something about the relative competence (or stiffness) of the till layer compared to the coarse clastics above. We also detected small thrust faults that are also parallel to the push-moraine, but these have very little offset and most of the deformation was achieved by folding.</p><p>Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.</p>

The Interpretation of Seismic Reflection Data from the Western Platform Region of Taranaki Basin

1988 ◽  
Vol 6 (2) ◽  
pp. 136-150 ◽  
Author(s):  
Glenn P. Thrasher
Keyword(s):  
Travel Time ◽  
Seismic Reflection ◽  
Time Data ◽  
Lateral Velocity ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Travel Time Data ◽  
Velocity Variations ◽  
Thickness Variations ◽  
Reflection Characteristics

The western-most region of Taranaki Basin, the Western Platform, has a stratigraphy which permits subdivision into major seismic units. The reflectors separating these units are easily identifiable. Each of the units and reflectors has typical reflection characteristics which are often correlatable with the lithology of the unit. Lateral velocity variations, caused by lateral deposition and compaction variations in prograding sequences, area major problem in developing depth conversion models for this region. Analysis of travel time data from wells shows that velocity variations in both the Oligocene-Miocene and Pliocene-Pleistocene sequences are predictable from the thickness variations of the units (and hence from interval travel times). The imerval velocity variations of the Paleocene-Eocene transgressive sequence are dependent on the overburden history and lithology of the unit.

Automating the acquisition of 3D near‐surface seismic reflection data

2009 ◽  
Author(s):  
Steven D. Sloan ◽  
Don W. Steeples ◽  
Georgios P. Tsoflias ◽  
Mihan H. McKenna
Keyword(s):  
Seismic Reflection ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data

Tomographic determination of velocity and depth in laterally varying media

Geophysics ◽  
1985 ◽  
Vol 50 (6) ◽  
pp. 903-923 ◽  
Author(s):  
T. N. Bishop ◽  
K. P. Bube ◽  
R. T. Cutler ◽  
R. T. Langan ◽  
P. L. Love ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Seismic Velocity ◽  
Real Data ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Tomographic Method ◽  
Recorded Data ◽  
The Difference

Estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem. The method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography. Seismic tomography is formulated as an iterative Gauss‐Newton algorithm that produces a velocity‐depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data. The input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first‐guess velocity‐depth model. Usually this first‐guess model has velocities which are laterally constant and is usually based on nearby well information and/or an analysis of the stacked section. The final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root‐mean‐square. The indeterminancy of the inversion and the associated nonuniqueness of the output model are both analyzed theoretically and tested numerically. It is found that certain aspects of the velocity field are poorly determined or undetermined. This technique is applied to an example using real data where the presence of permafrost causes a near‐surface lateral change in velocity. The permafrost is successfully imaged in the model output from tomography. In addition, depth estimates at the intersection of two lines differ by a significantly smaller amount than the corresponding estimates derived from conventional processing.

scholarly journals Seismic interferometry using multidimensional deconvolution and crosscorrelation for crosswell seismic reflection data without borehole sources

Geophysics ◽  
2011 ◽  
Vol 76 (1) ◽  
pp. SA19-SA34 ◽  
Author(s):  
Shohei Minato ◽  
Toshifumi Matsuoka ◽  
Takeshi Tsuji ◽  
Deyan Draganov ◽  
Jürg Hunziker ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Field Data ◽  
Time Lapse ◽  
P Wave ◽  
Source Distribution ◽  
Seismic Interferometry ◽  
Imaging Method ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Receiver Arrays

Crosswell reflection method is a high-resolution seismic imaging method that uses recordings between boreholes. The need for downhole sources is a restrictive factor in its application, for example, to time-lapse surveys. An alternative is to use surface sources in combination with seismic interferometry. Seismic interferometry (SI) could retrieve the reflection response at one of the boreholes as if from a source inside the other borehole. We investigate the applicability of SI for the retrieval of the reflection response between two boreholes using numerically modeled field data. We compare two SI approaches — crosscorrelation (CC) and multidimensional deconvolution (MDD). SI by MDD is less sensitive to underillumination from the source distribution, but requires inversion of the recordings at one of the receiver arrays from all the available sources. We find that the inversion problem is ill-posed, and propose to stabilize it using singular-value decomposition. The results show that the reflections from deep boundaries are retrieved very well using both the CC and MDD methods. Furthermore, the MDD results exhibit more realistic amplitudes than those from the CC method for downgoing reflections from shallow boundaries. We find that the results retrieved from the application of both methods to field data agree well with crosswell seismic-reflection data using borehole sources and with the logged P-wave velocity.

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 Depth characterization of shallow aquifers with seismic reflection, Part I—The failure of NMO velocity analysis and quantitative error prediction

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 89-97 ◽  
Author(s):  
John H. Bradford
Keyword(s):  
Layer Thickness ◽  
Water Table ◽  
Seismic Reflection ◽  
Negative Impact ◽  
Compressional Wave ◽  
Unconsolidated Sediments ◽  
Velocity Analysis ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Saturated Layer

As seismic reflection data become more prevalent as input for quantitative environmental and engineering studies, there is a growing need to assess and improve the accuracy of reflection processing methodologies. It is common for compressional‐wave velocities to increase by a factor of four or more where shallow, unconsolidated sediments change from a dry or partially water‐saturated regime to full saturation. While this degree of velocity contrast is rare in conventional seismology, it is a common scenario in shallow environments and leads to significant problems when trying to record and interpret reflections within about the first 30 m below the water table. The problem is compounded in shallow reflection studies where problems primarily associated with surface‐related noise limit the range of offsets we can use to record reflected energy. For offset‐to‐depth ratios typically required to record reflections originating in this zone, the assumptions of NMO velocity analysis are violated, leading to very large errors in depth and layer thickness estimates if the Dix equation is assumed valid. For a broad range of velocity profiles, saturated layer thickness will be overestimated by a minimum of 10% if the boundary of interest is <30 m below the water table. The error increases rapidly as the boundary shallows and can be very large (>100%) if the saturated layer is <10 m thick. This degree of error has a significant and negative impact if quantitative interpretations of aquifer geometry are used in aquifer evaluation such as predictive groundwater flow modeling or total resource estimates.

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