Removal of the detector‐ground coupling effect in the vertical seismic profiling environment

Geophysics ◽  
1988 ◽  
Vol 53 (3) ◽  
pp. 359-364 ◽  
Author(s):  
Paul C. Wuenschel
Keyword(s):  
Ground Motion ◽  
Frequency Band ◽  
Coupling Effect ◽  
Body Wave ◽  
The Body ◽  
Controlled Experiment ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Recorded Signal

In a “controlled” experiment with the Gulf VSP tool, the detector‐ground coupling was measured and removed from the recorded signal using the Washburn‐Wiley algorithm. Repeat measurements were made at a common detector depth with two coupling configurations, the first to permit the true ground motion to be recorded and the second to ensure that a coupling resonance existed within the seismic frequency band. The algorithm removed the distortion of the body‐wave portion of the seismogram caused by the coupling resonance for the second configuration and recovered true ground motion. However, lowering the coupling resonance into the seismic band also caused the tool to become sensitive to tube waves. This observation is helpful in evaluating current VSP tools; it implies that any VSP tool that is sensitive to tube waves has a coupling resonance within the seismic frequency band, and that the signal recorded with such a tool does not measure true ground motion. This test also showed that a detector used to monitor source signature variations must have a bandwidth comparable to the VSP signal.

An examination of tube wave noise in vertical seismic profiling data

Geophysics ◽  
1981 ◽  
Vol 46 (6) ◽  
pp. 892-903 ◽  
Author(s):  
B. A. Hardage
Keyword(s):  
Body Wave ◽  
Effective Means ◽  
Power Spectra ◽  
Effective Field ◽  
The Body ◽  
Seismic Profiles ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Vsp Data ◽  
Tube Wave

Tube waves act as noise that camouflages upgoing and downgoing body wave events which are the fundamental seismic data measured in vertical seismic profiling (VSP). In two onshore vertical seismic profiles, the principal source of tube waves is shown to be surface ground roll that sweeps across the well head. Secondary tube wave sources revealed in these VSP data are the downhole geophone tool itself and the bottom of the borehole. Body wave signals are also shown to create tube waves when they arrive at significant impedance contrasts in the borehole such as changes in casing diameter. Computer simulated vertical geophone arrays are used to reduce these tube waves, but such arrays attenuate and filter body wave events unless static time shifts are made so that the body wave signal occurs at the same two‐way time at each geophone station. Consequently, actual downhole vertical geophone arrays are not an effective means by which tube waves can be eliminated. Power spectra comparisons of tube wave and compressional body wave events demonstrate that band‐pass filters designed to eliminate tube waves also suppress body wave signals. A simple but effective field technique for reducing tube waves is shown to be proper source offset. Using velocity filters to retrieve upgoing compressional events from VSP data heavily contaminated with tube wave noise yields in one example an agreement with surface measured reflections that is superior to that obtained from synthetic seismograms calculated from log data recorded in the same well.

scholarly journals An extraction method of dispersion curve from vertical seismic profiling data

2020 ◽  
Author(s):  
Zhi Hu ◽  
Jinghuai Gao ◽  
Yanbin He ◽  
Guowei Zhang
Keyword(s):  
Dispersion Curve ◽  
Group Velocity ◽  
Body Wave ◽  
Seismic Signal ◽  
Time Frequency ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Wave Data ◽  
Vsp Data ◽  
The Relationship

Abstract The dispersion curve describes the relationship between velocities and frequencies. The group velocity is a kind of dispersion, which presents the velocities of the energy with different frequencies. Although many studies have shown methods for estimating group velocity from a surface wave, the estimation of group velocity from body-wave data is still hard. In this paper, we propose a method to calculate the group velocity from vertical seismic profiling (VSP) data that is a kind of body-wave data. The generalised S-transform (GST) is used to map the seismic signal to the time-frequency (TF) domain and then the group delay (GD) can be extracted from the TF domain. The GD shows the travelling time of different frequency components. The group velocity can be calculated by the GD and the distance between receivers. Unfortunately, the GD is hard to measure accurately because of the noise. Inaccurate GD introduces errors in estimating the velocity. To reduce the errors, we make use of the multiple traces and the iterative least-squares fitting to extract the relationship line between GD and depths. The slope of the line is the reciprocal of the group velocity. Two numerical examples prove the effectiveness of the method. We also derive the formula of group velocity in diffusive-viscous media. In the field data example, the dispersion intensity at different depths and the geological layers can be well matched. These examples illustrate the proposed method is an alternative method for dispersion estimation from VSP.

Precision of different varieties of magnitude

1972 ◽  
Vol 62 (3) ◽  
pp. 789-792
Author(s):  
B. F. Howell
Keyword(s):  
Surface Wave ◽  
Frequency Band ◽  
Wave Amplitude ◽  
Body Wave ◽  
The Body ◽  
Surface Wave Magnitude ◽  
Lower Standard ◽  
Standard Deviations ◽  
Body Wave Magnitude

Abstract The standard deviations of the body-wave magnitude, surface-wave magnitude and frequency-band magnitude of four shallow (H < 60 km) earthquakes are compared. For three out of four of these earthquakes, surface-wave magnitude exhibited lower standard deviations than either body-wave or frequency-band magnitude. In three out of the four cases, lower standard deviations were obtained by calculating surface-wave magnitude from the largest surface-wave amplitude than from time-correlated surface-wave phases.

The Mississippi Valley earthquakes of 1811 and 1812: Intesities, ground motion and magnitudes

1973 ◽  
Vol 63 (1) ◽  
pp. 227-248 ◽  
Author(s):  
Otto W. Nuttli
Keyword(s):  
North America ◽  
Ground Motion ◽  
Body Wave ◽  
Vertical Component ◽  
The Body ◽  
Eastern North America ◽  
Mississippi Valley ◽  
Isoseismal Map ◽  
Geological Conditions ◽  
Recent Earthquakes

abstract Contemporary newspaper accounts of the 1811-1812 Mississippi Valley earthquake sequence are used to construct a generalized isoseismal map of the first of three principal shocks of the sequence, that of December 16, 1811. The map is characterized by an unusually large felt area, with MM intensities of V as far away as the southeast Atlantic coastal area. By correlating the isoseismal map with that of recent earthquakes for which ground motion data are available, the body-wave magnitude of the December 16, 1811 earthquake is estimated to be 7.2. The other principal shocks, on January 23, 1812 and February 7, 1812, had estimated mb values of 7.1 and 7.4, respectively. The total energy released by the principal shocks and their larger-magnitude aftershocks is estimated to be equivalent to that of an mb = 7.5 (or Ms = 8.0) earthquake. The anomalously large areas of damage and of perceptibility of the principal shocks result from both the surficial geological conditions of the Mississippi Valley and the relatively low attenuation of surface-wave energy in eastern North America. Estimates of the vertical component of ground motion, for an earthquake of mb = 7.2 occurring in eastern North America, are given. These include values for particle velocity, displacement, and acceleration at frequencies of about 3, 1 and 0.3 Hz.

Fracture detection using P-wave and S-wave vertical seismic profiling at The Geysers

Geophysics ◽  
1988 ◽  
Vol 53 (1) ◽  
pp. 76-84 ◽  
Author(s):  
E. L. Majer ◽  
T. V. McEvilly ◽  
F. S. Eastwood ◽  
L. R. Myer
Keyword(s):  
Fractured Rock ◽  
Geothermal Field ◽  
P Wave ◽  
Velocity Variation ◽  
Fracture Detection ◽  
S Wave ◽  
Fracture Geometry ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
The Geysers

In a pilot vertical seismic profiling study, P-wave and cross‐polarized S-wave vibrators were used to investigate the potential utility of shear‐wave anisotropy measurements in characterizing a fractured rock mass. The caprock at The Geysers geothermal field was found to exhibit about an 11 percent velocity variation between SH-waves and SV-waves generated by rotating the S-wave vibrator orientation to two orthogonal polarizations for each survey level in the well. The effect is generally consistent with the equivalent anisotropy expected from the known fracture geometry.

Focal mechanism and source depth of earthquakes from body- and surface-wave data

1971 ◽  
Vol 61 (5) ◽  
pp. 1369-1379 ◽  
Author(s):  
Nezihi Canitez ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Source Parameters ◽  
Focal Depth ◽  
Spectral Ratio ◽  
The Body ◽  
Spectral Ratios ◽  
Motion Data ◽  
Wave Data ◽  
Surface Wave Data

abstract The determination of focal depth and other source parameters by the use of first-motion data and surface-wave spectra is investigated. It is shown that the spectral ratio of Love to Rayleigh waves (L/R) is sensitive to all source parameters. The azimuthal variation of the L/R spectral ratios can be used to check the fault-plane solution as well as for focal depth determinations. Medium response, attenuation, and source finiteness seriously affect the absolute spectra and introduce uncertainty into the focal depth determinations. These effects are nearly canceled out when L/R amplitude ratios are used. Thus, the preferred procedure for source mechanism studies of shallow earthquakes is to use jointly the body-wave data, absolute spectra of surface waves, and the Love/Rayleigh spectral ratios. With this procedure, focal depths can be determined to an accuracy of a few kilometers.

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