Shallow seismic investigation of a site with poor reflection quality

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1715-1726 ◽  
Author(s):  
Yih Jeng
Keyword(s):  
Seismic Energy ◽  
Dominant Frequency ◽  
P Wave ◽  
Sh Wave ◽  
P Waves ◽  
Frequency Bands ◽  
Energy Field ◽  
Reflection Data ◽  
Shallow Seismic ◽  
A Site

A shallow seismic reflection experiment was performed on a construction site to determine the feasibility of using reflection seismology to investigate the shallow structure in a weathered sand‐gravel interlayered zone that was known to be a poor transmission of high‐frequency seismic energy. Field‐recording parameters were designed to fit the limited space of the urban construction survey area. A 7 kg sledgehammer was used to generate P‐waves and SH‐waves. Single 100 Hz geophones were deployed at 1.0 m/0.5 m group intervals, and 200/100-Hz low‐cut filters were applied prior to A to D conversion to attenuate ground roll. For SH‐wave reflections, single 14 Hz geophones and a 70-Hz low‐cut filter on the seismograph were used. The dominant frequency bands ranged from 33 to 275 Hz and were centered around 110 Hz for P‐waves. Lower dominant frequency bands 20 to 160 Hz with a dominant frequency of around 85 Hz were observed on SH‐wave records. Four seismic lines, three P‐wave recordings and one SH‐wave recording, using different sets of recording parameters and an appropriate seismic‐wave generation method produced reflections from varying depth ranges and at different resolutions. The results show that the techniques employed in this experiment may resolve the structure of a site with poor reflection quality. An f-k dip filtering and deconvolution were necessary in processing the reflection data to eliminate various types of unwanted energy. The seismic interpretations in this study were verified by drilling and by a nearby excavation.

scholarly journals Field comparison of shallow P‐wave seismic sources near Houston, Texas

Geophysics ◽  
1994 ◽  
Vol 59 (11) ◽  
pp. 1713-1728 ◽  
Author(s):  
Richard D. Miller ◽  
Susan E. Pullan ◽  
Don W. Steeples ◽  
James A. Hunter
Keyword(s):  
Water Table ◽  
Seismic Source ◽  
Dominant Frequency ◽  
P Wave ◽  
Near Surface ◽  
Site Characteristics ◽  
Water Well ◽  
Local Water ◽  
A Site ◽  
Different Sources

A shallow P‐wave seismic source comparison was conducted at a site near Houston, Texas where the depth to the water table was approximately 7 m, and near‐surface materials consisted of clays, sands, and gravels. Data from twelve different sources during this November 1991 comparison are displayed and analyzed. Reflection events are interpretable at about 40 ms on some 220-Hz analog low‐cut filtered field files, and at 60 ms on most 110‐ and 220-Hz analog low‐cut filtered field files. Calculations and local water well information suggest the 40-ms event is from the top of the water table. Subsurface explosive sources seem to possess the highest dominant frequency, broadest bandwidth, and recorded amplitudes and, therefore, have the greatest resolution potential at this site. Our previous work and that of our colleagues suggests that, given a specific set of site characteristics, any source could dominate the comparison categories addressed here.

Mapping shallow faults at the Evrona playa site using high‐resolution reflection method

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1257-1264 ◽  
Author(s):  
Vladimir Shtivelman ◽  
Uri Frieslander ◽  
Ezra Zilberman ◽  
Rivka Amit
Keyword(s):  
High Resolution ◽  
Seismic Energy ◽  
Morphological Features ◽  
Geological Mapping ◽  
P Wave ◽  
Aerial Photographs ◽  
Seismic Survey ◽  
Good Correspondence ◽  
Reflection Data ◽  
Seismic Sections

A shallow high‐resolution seismic reflection survey was carried out at the Evrona playa site in the southern Arava valley, Israel. The aim of the survey was to detect and map faults in the shallow subsurface (upper 100–150 m) and establish the relationship of the morphological features revealed by aerial photographs and surface geological mapping with the faults detected in the subsurface. The survey included three seismic lines shot using the P-wave technique and one SH-wave line, which overlapped one of the P-wave lines. The seismic energy source on all the lines was a sledge hammer. The acquired reflection data were of good quality and did not require special processing efforts. The seismic sections along the lines show a sequence of reflected events within the 8–150 m range. At several locations, continuity of the events is interrupted by a system of faults. These faults form flower structures apparently related to strike‐slip motions typical of the region. Comparison of the faults mapped on the seismic sections with those expressed by surface morphological features generally show good correspondence. The results of the seismic survey provide important information for the study of paleoseismicity and seismic hazards in the investigated area.

scholarly journals Wet and gassy zones in a municipal landfill from P- and S-wave velocity fields

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. EN75-EN86 ◽  
Author(s):  
Laura Amalia Konstantaki ◽  
Ranajit Ghose ◽  
Deyan Draganov ◽  
Timo Heimovaara
Keyword(s):  
Wave Velocity ◽  
Gas Flow ◽  
Velocity Fields ◽  
P Wave ◽  
S Wave ◽  
P Waves ◽  
Municipal Landfill ◽  
Reflection Data ◽  
Tip Resistance ◽  
Surface Wave Data

The knowledge of the distribution of leachate and gas in a municipal landfill is of vital importance to the landfill operators performing improved landfill treatments and for environmental protection and efficient biogas extraction. We have explored the potential of using the velocity fields of seismic S- and P-waves to delineate the wet and gassy (relatively dry, gas/air-filled) zones inside a landfill. We have analyzed shallow S- and P-wave reflection data and seismic surface-wave data acquired at a very heterogeneous landfill site, where biogas was extracted. A joint interpretation of the independently estimated velocity fields from these various approaches has allowed us to localize anomalously low- and high-velocity zones in the landfill. From the complementary information provided by P- and S-wave velocity fields, we have inferred the leachate-bearing wet zones and the gassy zones inside the landfill. Independent measurements of gas flow and mechanical tip resistance to waste deformation validate our seismic interpretations.

Interpretation of a vertical seismic profile conducted in the Columbia Plateau basalts

Geophysics ◽  
1989 ◽  
Vol 54 (10) ◽  
pp. 1258-1266 ◽  
Author(s):  
J. Pujol ◽  
B. N. Fuller ◽  
S. B. Smithson
Keyword(s):  
Large Amplitude ◽  
Volcanic Rocks ◽  
Seismic Energy ◽  
Seismic Profile ◽  
P Wave ◽  
Low Velocity ◽  
P Waves ◽  
Seismic Reflection Data ◽  
S Waves ◽  
Columbia Plateau

Seismic reflection data are often of poor quality when recorded in areas where volcanic rocks are present at or near the surface. In order to investigate this phenomenon, a vertical seismic profiling (VSP) experiment was conducted in the Columbia Plateau basalts so that the behavior of seismic energy in subsurface volcanic rocks could be observed directly, thus giving insight into data acquisition in volcanic terrains. The lithologic section at the VSP site consists of low‐velocity (400 m/s to 900 m/s) alluvium in the uppermost 50 m, beneath which are layers of high‐velocity (about 5800 m/s), high‐density basalts interbedded with clay layers with much lower velocities (about 1700 m/s) and densities. These large velocity and density contrasts dramatically influence wave generation and propagation. In spite of the small source‐borehole offset (61 m), large‐amplitude S waves are generated by the downgoing P waves when they reach a shallow (250 m) clay‐basalt boundary. These S waves, in turn, generate strong reflected P waves when they interact with another clay layer at 500 m. On the other hand, strong primary P‐wave reflections are also present in the data but are affected by various interfering effects which reduce their amplitudes. The VSP data are also characterized by large‐amplitude reverberations caused by seismic energy trapped in the upper 250 m of the lithologic section. Reverberations are also observed in surface data recorded near the VSP site. We conclude from our analysis that volcanic rocks, at least in the Columbia Plateau, do not exhibit unusual energy transmission characteristics and that the observations can be explained in terms of the large contrast in the elastic properties of interbedded clay and basalt.

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.

Structural interpretation using refraction velocities from marine seismic surveys

Geophysics ◽  
1986 ◽  
Vol 51 (1) ◽  
pp. 12-19 ◽  
Author(s):  
James F. Mitchell ◽  
Richard J. Bolander
Keyword(s):  
Sedimentary Rock ◽  
Seismic Energy ◽  
Seismic Survey ◽  
Subsurface Structure ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Wide Range ◽  
Streamer Length ◽  
Set Up

Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.

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