scholarly journals Geochemistry and related studies of Clyde Estuary sediments

2017 ◽  
Vol 108 (2-3) ◽  
pp. 269-288 ◽  
Author(s):  
David G. Jones ◽  
Christopher H. Vane ◽  
Solveigh Lass-Evans ◽  
Simon Chenery ◽  
Bob Lister ◽  
...  
Keyword(s):  
Seismic Data ◽  
Surface Sediments ◽  
Sidescan Sonar ◽  
Near Surface ◽  
Glacial Sediments ◽  
Shallow Seismic ◽  
Limited Success ◽  
Shallow Layer ◽  
Quaternary History ◽  
Different Sources

ABSTRACTGeochemical and related studies have been made of near-surface sediments from the River Clyde estuary and adjoining areas, extending from Glasgow to the N, and W as far as the Holy Loch on the W coast of Scotland, UK. Multibeam echosounder, sidescan sonar and shallow seismic data, taken with core information, indicate that a shallow layer of modern sediment, often less than a metre thick, rests on earlier glacial and post-glacial sediments. The offshore Quaternary history can be aligned with onshore sequences, with the recognition of buried drumlins, settlement of muds from quieter water, probably behind an ice dam, and later tidal delta deposits. The geochemistry of contaminants within the cores also indicates shallow contaminated sediments, often resting on pristine pre-industrial deposits at depths less than 1m. The distribution of different contaminants with depth in the sediment, such as Pb (and Pb isotopes), organics and radionuclides, allow chronologies of contamination from different sources to be suggested. Dating was also attempted using microfossils, radiocarbon and 210Pb, but with limited success. Some of the spatial distribution of contaminants in the surface sediments can be related to grain-size variations. Contaminants are highest, both in absolute terms and in enrichment relative to the natural background, in the urban and inner estuary and in the Holy Loch, reflecting the concentration of industrial activity.

scholarly journals Effects of soil‐moisture content on shallow‐seismic data

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1357-1362 ◽  
Author(s):  
Robert D. Jefferson ◽  
Don W. Steeples ◽  
Ross A. Black ◽  
Tim Carr
Keyword(s):  
Soil Moisture ◽  
Moisture Content ◽  
Seismic Data ◽  
Soil Moisture Content ◽  
Soil Conditions ◽  
Near Surface ◽  
Surface Moisture ◽  
Shallow Seismic ◽  
Unconsolidated Material ◽  
Moisture Conditions

Repeated shallow‐seismic experiments were conducted at a site on days with different near‐surface moisture conditions in unconsolidated material. Experimental field parameters remained constant to ensure comparability of results. Variations in the seismic data are attributed to the changes in soil‐moisture content of the unconsolidated material. Higher amplitudes of reflections and refractions were obtained under wetter near‐surface conditions. An increase in amplitude of 21 dB in the 100–300 Hz frequency range was observed when the moisture content increased from 18% to 36% in the upper 0.15 m (0.5 ft) of the subsurface. In the time‐domain records, highly saturated soil conditions caused large‐amplitude ringy wavelets that interfered with and degraded the appearance of some of the reflection information in the raw field data. This may indicate that an intermediate near‐surface moisture content is most conducive to the recording of high‐quality shallow‐seismic reflection data at this site. This study illustrates the drastic changes that can occur in shallow‐seismic data due to variations in near‐surface moisture conditions. These conditions may need to be considered to optimize the acquisition timing and parameters prior to collection of data.

Effects of near‐surface waveguides on shallow seismic data

1995 ◽  
Author(s):  
Johan O. A. Robertsson ◽  
Andre' Pugin ◽  
Klaus Holliger ◽  
Alan G. Green
Keyword(s):  
Seismic Data ◽  
Near Surface ◽  
Shallow Seismic

scholarly journals Field comparison of shallow seismic sources near Chino, California

Geophysics ◽  
1992 ◽  
Vol 57 (5) ◽  
pp. 693-709 ◽  
Author(s):  
Richard D. Miller ◽  
Susan E. Pullan ◽  
Don W. Steeples ◽  
James A. Hunter
Keyword(s):  
Water Table ◽  
Seismic Source ◽  
Test Site ◽  
Single Site ◽  
Seismic Sources ◽  
Near Surface ◽  
Shallow Seismic ◽  
Site Characteristics ◽  
Weight Drop ◽  
Different Sources

Data from a shallow seismic‐source comparison test conducted in an area with a water‐table depth in excess of 30 m and near‐surface velocities less than 330 m/s were acquired from 13 different sources at a single site near Chino, California. The sources included sledgehammer, explosives, weight drop, projectile impacts, and various buffalo guns. A possible reflecting event can be interpreted at about 70 ms. At this particular test site, the lowly sledgehammer is among the best sources to provide data to see the possible reflection. Our previous work and that of our colleagues suggests that any source could dominate the comparison categories addressed here, given the appropriate set of site characteristics.

Improving imaging and repeatability on land using virtual source redatuming with shallow buried receivers

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. Q15-Q26 ◽  
Author(s):  
Dmitry Alexandrov ◽  
Andrey Bakulin ◽  
Roy Burnstad ◽  
Boris Kashtan
Keyword(s):  
Seismic Data ◽  
Near Field ◽  
Time Lapse ◽  
Elastic Model ◽  
Virtual Source ◽  
Field Zone ◽  
Near Surface ◽  
Actual Field ◽  
Different Sources

Time-lapse surface seismic monitoring typically suffers from different sources of nonrepeatability related to acquisition imperfections as well as due to complexity of the subsurface. Placing sources and receivers below the surface can improve seismic data repeatability. However, it is not always possible to bury a large number of sources, and therefore the next best option is monitoring with surface sources and buried sensors. We have discovered that redatuming of surface sources to the shallow buried receivers produced a reliable image of target reflectors despite the fact that receivers were placed in the near-field zone of the source. We redatumed data with the virtual source method using crosscorrelation of the measured wavefields. We found that redatuming also reduced nonrepeatability of seismic data associated with changes in acquisition geometry, variable source coupling, and daily/seasonal variations in the near surface. We developed these results with a synthetic case study using a realistic 1D elastic model with a free surface and acquisition geometry from an actual field experiment conducted in Saudi Arabia.

scholarly journals Time-lapse imaging of CO2 migration within near-surface sediments during a controlled sub-seabed release experiment

2021 ◽  
Vol 109 ◽  
pp. 103363
Author(s):  
Ben Roche ◽  
Jonathan M. Bull ◽  
Hector Marin-Moreno ◽  
Timothy G. Leighton ◽  
Ismael H. Falcon-Suarez ◽  
...  
Keyword(s):  
Surface Sediments ◽  
Time Lapse ◽  
Near Surface ◽  
Release Experiment ◽  
Time Lapse Imaging

Regularization and datuming of seismic data by weighted, damped least squares

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. U67-U76 ◽  
Author(s):  
Robert J. Ferguson
Keyword(s):  
Least Squares ◽  
Seismic Data ◽  
Synthetic Data ◽  
Real Data ◽  
Structural Data ◽  
Irregular Sampling ◽  
Data Set ◽  
Near Surface ◽  
Damped Least Squares ◽  
Wavefield Extrapolation

The possibility of improving regularization/datuming of seismic data is investigated by treating wavefield extrapolation as an inversion problem. Weighted, damped least squares is then used to produce the regularized/datumed wavefield. Regularization/datuming is extremely costly because of computing the Hessian, so an efficient approximation is introduced. Approximation is achieved by computing a limited number of diagonals in the operators involved. Real and synthetic data examples demonstrate the utility of this approach. For synthetic data, regularization/datuming is demonstrated for large extrapolation distances using a highly irregular recording array. Without approximation, regularization/datuming returns a regularized wavefield with reduced operator artifacts when compared to a nonregularizing method such as generalized phase shift plus interpolation (PSPI). Approximate regularization/datuming returns a regularized wavefield for approximately two orders of magnitude less in cost; but it is dip limited, though in a controllable way, compared to the full method. The Foothills structural data set, a freely available data set from the Rocky Mountains of Canada, demonstrates application to real data. The data have highly irregular sampling along the shot coordinate, and they suffer from significant near-surface effects. Approximate regularization/datuming returns common receiver data that are superior in appearance compared to conventional datuming.

Sign in / Sign up

Export Citation Format

Share Document