High‐resolution seismic reflections in a potash mine

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 741-748 ◽  
Author(s):  
D. J. Gendzwill ◽  
Randy Brehm
Keyword(s):  
High Resolution ◽  
Sampling Rate ◽  
Seismic Source ◽  
Dominant Frequency ◽  
Unexpected Result ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Shear Wave Speed ◽  
Seismic Reflections ◽  
Potash Mine

High‐resolution seismic reflections underground in a deep potash mine in Canada have been collected using a hammer for a seismic source, 50 Hz geophones, and a digital, stacking seismograph with 0.1 ms sampling rate. Data were obtained with 12‐fold redundancy in both downward and upward directions from the mine openings. Reflections with dominant frequency up to 1100 Hz were observed between 20 and 80 ms time. Both single geophones and arrays of geophones were tested. For the roof profiles, geophones were bolted to the rock with specially designed base plates. Computer processing used deconvolution filters to remove spurious high‐frequency resonance of the geophones. Constant velocity for salt was used for all static corrections and normal moveout corrections. An unexpected result was the appearance of near‐vertical reflected waves that traveled both ways at the shear‐wave speed. These are thought to have been caused by near‐surface fractures or near‐surface anisotropy of the rock. Synthetic seismograms calculated from logs of a nearby well agree with the seismic reflection data. Normal stratification of the flat‐bedded sedimentary rocks and a small structure were mapped by the seismic data, confirming the vertical extent of geological anomalies observed at the mine level.

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.

High‐resolution images of shallow aquifers—A challenge in near‐surface seismology

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 177-187 ◽  
Author(s):  
Roberto G. Francese ◽  
Zoltan Hajnal ◽  
Arnfinn Prugger
Keyword(s):  
High Resolution ◽  
Processing Parameters ◽  
Borehole Data ◽  
Coherent Noise ◽  
Seismic Section ◽  
Near Surface ◽  
Management Area ◽  
Data Acquisition Program ◽  
Sandy Aquifers ◽  
Potash Mine

A near‐surface multifold high‐resolution seismic reflection experiment was conducted in the vicinity of the waste management area of a potash mine in western Canada. A buried channel was identified in the data, and the stratigraphy of the Quaternary infill of this structure was mapped. The spatial extent of several prominent gravel‐sandy aquifers, which represent the hydrogeologic framework of the region, was outlined by the survey. The seismic signatures also established the hydraulic independence of three major aquifers along the survey line. The complex heterogeneous lithology of the surface cover limited effective elastic‐wave generation to surface sources. This geologic framework also caused propagation of strong diverse coherent‐noise patterns which severely degraded reflected signal. The suppression of those overhelming interfering events required the design of noise‐specific filters and their sequential multistep implementations. Results of forward modeling of background geologic information were crucial factors in the design of the data acquisition program and preliminary choices of the processing parameters, and (along with borehole data) were the primary guidance in the geologic interpretation of the final seismic section. Fundamental procedures were developed for mapping of glacial tills in the Western Canadian Basin, techniques that can be applied in other regions with similar near‐surface glacial stratigraphy. The experiment revealed that even closely spaced borehole information could never duplicate the detail of the subsurface images of the seismic data.

Detecting Karst Voids Based on Dominant Frequencies of Seismic Profiles

2021 ◽  
Author(s):  
Ying Rao ◽  
Yongxin Guo ◽  
Duo Xu
Keyword(s):  
High Resolution ◽  
Frequency Spectrum ◽  
High Speed ◽  
Dominant Frequency ◽  
Frequency Function ◽  
Resolution Time ◽  
High Speed Rail ◽  
Karst Terrain ◽  
Near Surface ◽  
Time Frequency

AbstractThe presence of near-surface karst voids is an extremely difficult issue in the construction of a high-speed rail (HSR) foundation. Seismic constant-offset profile (COP) method is one of the shallow geophysics technologies which may be used for the detection of karst voids. Although a COP image does not directly reveal the characters related to the anomalies in a karst terrain, the dominant frequency of the COP image in a karst terrain is significantly lower than the dominant frequency over the background without karstification or voids. This dominant-frequency anomaly is due to the strong attenuation effect when seismic waves propagate through any karst voids. Thus, we propose using the dominant-frequency anomalies of the COP image to directly detect near-surface karst voids in a karst terrain. First, we generate a high-resolution time–frequency spectrum for each COP trace, using the modified Wigner-Ville distribution (WVD) algorithm which combines WVD with a multichannel maximum entropy method. Second, we estimate a high-precision dominant-frequency function which varies along the reflection time, based on the corresponding high-resolution time–frequency spectrum. Finally, we detect the geological anomalies by analyzing low-frequency distributions in the dominant-frequency image for all traces. We demonstrate this procedure with a case study for the detection of karst voids within the high-speed rail foundation in a karst terrain, and verify the interpretation of hidden voids, cavities, clays and peats directly with drilling cores.

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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