Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1295-1309 ◽  
Author(s):  
Ranajit Ghose ◽  
Vincent Nijhof ◽  
Jan Brouwer ◽  
Yoshikazu Matsubara ◽  
Yasuhiro Kaida ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Waves ◽  
Soft Soil ◽  
Geophysical Methods ◽  
Seismic Source ◽  
P Wave ◽  
Nondestructive Technique ◽  
Buried Objects ◽  
Reflection Seismic

In shallow engineering‐geophysical applications, there is a lack of controlled, nondestructive, high‐resolution mapping tools, particularly for the target depth that ground‐penetrating radar cannot reach but which is too shallow for other conventional geophysical methods. For soft soil, this corresponds to a depth of 2 to 30 m. We have developed a portable, high‐frequency P-wave vibrator system that is capable of bridging this gap. As far as the important contribution of the seismic source is concerned, penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator. The feasibility of this system has been tested in shallow (10–50 m) to very shallow (0–10 m) applications. Seven field data sets representing varying geology, site conditions, and exploration targets are presented to illustrate the applicability. The first three examples show the potential of this portable vibrator source in shallow applications. Under favorable situations, a maximum resolution of about 20 cm for events located at 15–30 m depth could be achieved. Because high‐frequency seismic waves suffer from severe attenuation in the dry, unsaturated weathered zone, the penetration is relatively limited when the water table is deeper than 4–5 m. The fourth to seventh field examples illustrate very shallow applications at noisy, asphalt‐paved urban sites that are often encountered in civil, geotechnical, and environmental engineering projects. The prospecting targets were thin soil layers or small buried objects. On asphalt, the vibrator can produce high‐frequency energy easily. The fourth example shows high‐resolution delineation of very shallow soil structures. The last three examples present successful location of buried bodies—often small and closely spaced—in soft soil at depths of 0.5 to 5 m. We observe well‐defined reflection events of frequency exceeding 200 Hz. These results suggest that high‐frequency seismic reflection imaging using the portable vibrator system can indeed serve as a powerful, nondestructive technique for shallow to very shallow underground prospecting.

Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany

2021 ◽  
Author(s):  
Ulrich Polom ◽  
Rebekka Mecking ◽  
Phillip Leineweber ◽  
Andreas Omlin
Keyword(s):  
High Resolution ◽  
Water Resources ◽  
Industrial Development ◽  
Geophysical Methods ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Depth Range ◽  
Reflection Seismic ◽  
Wide Range ◽  
Cap Rock

<p>In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.</p><p>Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.</p>

The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 78-89 ◽  
Author(s):  
Donat Demanet ◽  
François Renardy ◽  
Kris Vanneste ◽  
Denis Jongmans ◽  
Thierry Camelbeeck ◽  
...  
Keyword(s):  
High Resolution ◽  
Physical Properties ◽  
Fault Zone ◽  
Geophysical Methods ◽  
Depth Range ◽  
Electrical Tomography ◽  
Reflection Seismic ◽  
Refraction Seismic ◽  
Geophysical Surveys ◽  
Geophysical Techniques

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change in the water table depth across the fault. Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters. In a second step, more detailed methods (electrical tomography and GPR) more precisely imaged the fault zone and revealed some structures that were observed in the trenches. Finally, one high‐resolution reflection seismic profile imaged the displacement of the fault at depths as large as 120 m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques. Like all geophysical surveys, the quality of the data is strongly dependent on the geologic environment and on the contrast of the physical properties between the juxtaposed formations. The combined use of various geophysical techniques is thus recommended for fault mapping, particularly for a preliminary investigation when the geological context is poorly defined.

scholarly journals Subsurface characterization of a quick-clay vulnerable area using near-surface geophysics and hydrological modelling

Solid Earth ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 1685-1705
Author(s):  
Silvia Salas-Romero ◽  
Alireza Malehmir ◽  
Ian Snowball ◽  
Benoît Dessirier
Keyword(s):  
Large Scale ◽  
Geophysical Methods ◽  
Hydrological Modelling ◽  
P Wave ◽  
Coarse Grained ◽  
Near Surface ◽  
Reflection Seismic ◽  
Geotechnical Investigations ◽  
Quick Clay ◽  
Near Surface Geophysics

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 m s−1 and resistivity from approximately 80 to 100 Ωm) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow–outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.

scholarly journals The development and initial field trials of a new high frequency seismic vibrator

1989 ◽  
Vol 20 (2) ◽  
pp. 163
Author(s):  
D.B. Stewart ◽  
M.R. Seman
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Broad Band ◽  
Seismic Source ◽  
Field Trials ◽  
Electronic Control ◽  
Initial Field ◽  
Frequency Wave ◽  
The Cost ◽  
Zero Phase

The cost of shot hole drilling is often more expensive than using vibratory energy sources in high resolution seismic surveying. However, such costs are often accepted since conventional vibrators cannot always provide the extreme imaging capacity required in high resolution work. Conventional seismic vibrators sweep in a range from 5 Hz to 250 Hz ? the range of which is limited by the vibrator. The impulse train of the high resolution wacker used by the MiniSOSIE1 system is also band limited, causing a reduction in imaging resolution. The ideal solution is to sweep a broad range of frequencies from the lower seismic range to as high as 500 Hz. This could offer a cost effective solution to the acquisition of broad band high resolution data. In high resolution seismic profiling, explosives are commonly used as the source. Small charges below the weathered layer produce the highest frequency content (Ziolkowski and Lerwill, 1979). Unfortunately, the cost of drilling shot holes is a major component of the survey costs. For oil exploration in Australia/New Zealand, dynamite surveys average 43% more than Vibroseis2 surveys in dollars per kilometre (Montgomery, 1987), despite more hardware being required for Vibroseis recording.The MiniSOSIE system is also used for some high resolution surveys, because it is relatively cheap. However, this does not achieve equivalent results to small explosives. It will give worse results as the soil becomes softer, as the rebound from an impact takes longer, and hence the wavelet is broader.An alternative to these sources is the hydraulic powered vibrator, which has sometimes been used for high resolution coal work in Europe. With vibrators, the spectrum is controllable within certain limits. The Vibroseis system can also produce zero phase wavelets, if used properly with its controllable frequency wave-train sweep; and with repeatable multiple sweeps this results in enhancement of signal to noise ratio together with the promise of the highest frequency returns. Zero phase wavelets have slightly better resolution than the same bandwidth minimum phase wavelets as produced by impulsive sources. The breadth (t) of a zero phase Klauder wavelet with a boxcar spectrum can be predicted from the sweep start (fS) and end (fE) frequencies by the approximation: [see full text for equation]. By sweeping 50 to 500 Hz, a wavelet 1.8 ms wide should result, which is the resolution required to locate faults with a throw of less than two metres. In practice, a wider wavelet may be obtained, due to absorption of the high frequency energy. The Vibrator Seismic Source (VSS) is presented here in its first application of this new hydraulic powered vibratory source, which operates under different mechanical and electronic control than used heretofore by conventional vibratory sources. The VSS has been developed continuously since 1980 when an initial grant was received from NERDDC. During the intervening years till 1987, two more grants were received (Stewart, 1988). A recent further NERDDC grant was received in 1988 jointly by ACIRL, Curtin University and University College ADFA for areal coal seam mapping by three-dimensional seismic reflection surveying, with an emphasis on high resolution imaging of faults. The novelty of the VSS lies in the use of a single flow path for hydraulic oil through the flow stage of a Servo Popper Valve (SPV) (Stewart, 1986). This powers the vibrator by application of the oil to only one side of a piston in the linear actuator which produces the forced output of the vibrator on the surface of the earth. Conventional vibrators use a spool valve to alternately reverse the flow of oil into opposite chambers of a double acting cylinder. Hence the VSS has a fluid power advantage over conventional vibrators and this is evident by better performance at the higher frequencies. The VSS can sweep typically from 50 Hz to 500 Hz, and was initially field tested as a high resolution energy source. Innovations in both mechanical and electronic control systems are presented and results of the initial field trials of the VSS are compared to explosive seismic source results. 1Trade Mark of CGG 2Trade Mark of Conoco

A simple method for determining the S80 water gun depth

Geophysics ◽  
1986 ◽  
Vol 51 (2) ◽  
pp. 424-426 ◽  
Author(s):  
M. H. Safar
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Source ◽  
Frequency Signal ◽  
High Frequency Signal ◽  
Simple Method ◽  
Marine Oil ◽  
Principal Reason ◽  
Air Gun ◽  
High Level

The water gun, which is becoming a popular seismic source, has proven to be an important development in marine oil prospecting. The principal reason is that, unlike the air gun, the pressure signature radiated by the water gun consists of a single bubble pulse and contains a high level of high‐frequency signal. These important features make the water gun a suitable seismic source for high‐resolution surveys. Water guns currently used are the S80, which has been used by Horizon since 1977, and the P400, introduced in 1983. The S80 and P400 water guns were developed by Sodera.™

High‐resolution crosswell imaging of a west Texas carbonate reservoir: Part 1—Project summary and interpretation

Geophysics ◽  
1995 ◽  
Vol 60 (3) ◽  
pp. 667-681 ◽  
Author(s):  
Jerry M. Harris ◽  
Richard C. Nolen‐Hoeksema ◽  
Robert T. Langan ◽  
Mark Van Schaack ◽  
Spyros K. Lazaratos ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Large Scale ◽  
Carbonate Reservoir ◽  
P Wave ◽  
Small Scale ◽  
Observation Well ◽  
Traveltime Tomography ◽  
Seismic Profiling ◽  
West Texas

A carbon dioxide flood pilot is being conducted in a section of Chevron’s McElroy field in Crane County, west Texas. Prior to [Formula: see text] injection, two high‐frequency crosswell seismic profiles were recorded to investigate the use of seismic profiling for high‐resolution reservoir delineation and [Formula: see text] monitoring. These preinjection profiles provide the baseline for time‐lapse monitoring. Profile #1 was recorded between an injector well and an offset observation well at a nominal well‐to‐well distance of 184 ft (56 m). Profile #2 was recorded between a producing well and the observation well at a nominal distance of 600 ft (183 m). The combination of traveltime tomography and stacked CDP reflection amplitudes demonstrates how high‐frequency crosswell seismic data can be used to image both large and small scale heterogeneity between wells: Transmission traveltime tomography is used to image the large scale velocity variations; CDP reflection imaging is then used to image smaller scale impedance heterogeneities. The resolution capability of crosswell data is clearly illustrated by an image of the Grayburg‐San Andres angular unconformity, seen in both the P‐wave and S‐wave velocity tomograms and the reflection images. In addition to the imaging study, cores from an observation well were analyzed to support interpretation of the crosswell images and assess the feasibility of monitoring changes in [Formula: see text] saturation. The results of this integrated study demonstrate (1) the use of crosswell seismic profiling to produce a high‐resolution reservoir delineation and (2) the possibility for successful monitoring of [Formula: see text] in carbonate reservoirs. The crosswell data were acquired with a piezoelectric source and a multilevel hydrophone array. Both profiles, nearly 80 000 seismic traces, were recorded in approximately 80 hours using a new acquisition technique of shooting on‐the‐fly. This paper presents the overall project summary and interpretation of the results from the near‐offset profile.

Seismic radiation from a point source on the surface of a cylindrical cavity

Geophysics ◽  
1978 ◽  
Vol 43 (6) ◽  
pp. 1071-1082 ◽  
Author(s):  
Roy J. Greenfield
Keyword(s):  
Cylindrical Cavity ◽  
High Frequency ◽  
Seismic Source ◽  
P Wave ◽  
Point Force ◽  
Shielding Effect ◽  
S Wave ◽  
Source Data ◽  
Mine Roof ◽  
Direction Opposite

The presence of a void or cavity in the vicinity of a seismic source will modify the radiated signal from the classic solution for a point force in an infinite medium. To study this effect, solutions were obtained for the seismic fields from a point force applied to the surface of a cylindrical cavity in an elastic medium. The solutions were evaluated to give P‐ and S‐wave frequency domain radiation patterns. For P wavelengths less than about 3 times the cavity diameter, the cavity acts to decrease the P‐wave amplitude going outward in the direction opposite the source. Data taken in two coal mines show this shielding effect. High‐frequency energy was observed, with surface seismometers, for signals generated by hitting the mine roof, whereas the high‐frequency energy was much smaller on signals generated by hitting the floor. Time domain calculations show that the P‐wave signal is delayed by approximately the time it takes an S‐wave to propagate around the cylinder.

scholarly journals 3-D seismic travel-time tomography validation of a detailed subsurface model: a case study of the Záncara river basin (Cuenca, Spain)

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 177-192
Author(s):  
David Marti ◽  
Ignacio Marzan ◽  
Jana Sachsenhausen ◽  
Joaquina Alvarez-Marrón ◽  
Mario Ruiz ◽  
...  
Keyword(s):  
High Resolution ◽  
Travel Time ◽  
River Basin ◽  
Seismic Velocity ◽  
Underground Structure ◽  
High Capacity ◽  
Seismic Source ◽  
P Wave ◽  
Shallow Subsurface ◽  
Travel Time Tomography

Abstract. A high-resolution seismic tomography survey was acquired to obtain a full 3-D P-wave seismic velocity image in the Záncara river basin (eastern Spain). The study area consists of lutites and gypsum from a Neogene sedimentary sequence. A regular and dense grid of 676 shots and 1200 receivers was used to image a 500 m×500 m area of the shallow subsurface. A 240-channel system and a seismic source, consisting of an accelerated weight drop, were used in the acquisition. Half a million travel-time picks were inverted to provide the 3-D seismic velocity distribution up to 120 m depth. The project also targeted the geometry of the underground structure with emphasis on defining the lithological contacts but also the presence of cavities and fault or fractures. An extensive drilling campaign provided uniquely tight constraints on the lithology; these included core samples and wireline geophysical measurements. The analysis of the well log data enabled the accurate definition of the lithological boundaries and provided an estimate of the seismic velocity ranges associated with each lithology. The final joint interpreted image reveals a wedge-shaped structure consisting of four different lithological units. This study features the necessary key elements to test the travel time tomographic inversion approach for the high-resolution characterization of the shallow subsurface. In this methodological validation test, travel-time tomography demonstrated to be a powerful tool with a relatively high capacity for imaging in detail the lithological contrasts of evaporitic sequences located at very shallow depths, when integrated with additional geological and geophysical data.

Seismic source spectrum of microearthquakes

1992 ◽  
Vol 82 (6) ◽  
pp. 2391-2409
Author(s):  
Yoshihisa Iio
Keyword(s):  
Wave Velocity ◽  
High Frequency ◽  
Hard Rock ◽  
Ground Surface ◽  
Seismic Source ◽  
P Wave ◽  
Source Spectrum ◽  
Anelastic Attenuation ◽  
P Wave Velocity ◽  
Source Spectra

Abstract The seismic source spectra of microearthquakes having seismic moments between 1014 and 1018 dyne cm were investigated by using local recordings from an excellent hard-rock site. The P-wave velocity near the site was estimated as about 6 km/sec, even immediately below the ground surface. The effect of anelastic attenuation was thought to be very small, since predominant frequencies of greater than 100 Hz were detected in seismograms recorded at focal distances greater 10 km. Many seismograms with S-P times of less than 0.6 sec were observed. The first cycle of the P-wave velocity seismogram was used in this study. The waveforms after the first cycle are likely formed near the site, since their periods are exactly the same for earthquakes that have different source processes. In the high-frequency portion of the estimated displacement source spectra, the slopes of the fall-off have values much greater than 2. The source process of microearthquakes is assumed to be very slow and smooth.

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