Circularly polarized shear waves used for VSP measurements

Geophysics ◽  
1992 ◽  
Vol 57 (4) ◽  
pp. 643-646
Author(s):  
Hans A. K. Edelmann
Keyword(s):  
Shear Wave ◽  
Velocity Ratio ◽  
Shear Waves ◽  
Signal Amplitude ◽  
P Wave ◽  
Polarization Analysis ◽  
S Wave ◽  
P Waves ◽  
Additional Processing ◽  
Wave Recording

If shear waves are to be recorded, all other types of waves (including P waves) have to be regarded as noise. All data processing applied later is limited in its success, not so much by the character of the signal, but by the character of the noise superimposed on the signal. Therefore an optimum method for simultaneous P‐ and S‐wave recording does not exist per se. All efforts made in the field that help to enhance the relatively weak S‐wave signal enhance the possibility of a more detailed interpretation such as polarization analysis. In the course of shear‐wave investigations over a period of more than ten years, simultaneous P‐ and SV‐wave recording has yielded fairly good results for velocity ratio determination, but has never produced satisfying results for polarization analysis because of the interfering P‐wave events. When generating pure SH‐waves, however, P‐wave arrival amplitudes in a shot record can, under favorable conditions, be kept well below the SH‐wave amplitude (−40 dB). Through additional processing, a ratio of P‐ to SH‐signal amplitude of −60 dB can be reached. The improvement achieved by making separate shear‐wave recordings, obviously, must be weighed against the additional costs caused by these recordings.

High-frequency borehole seismograms recorded in the San Jacinto Fault zone, Southern California. Part 1. Polarizations

1991 ◽  
Vol 81 (4) ◽  
pp. 1057-1080 ◽  
Author(s):  
Richard C. Aster ◽  
Peter M. Shearer
Keyword(s):  
Shear Wave ◽  
Fault Zone ◽  
Particle Motion ◽  
Southern California ◽  
Shear Waves ◽  
P Wave ◽  
S Wave ◽  
Near Surface ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone

Abstract Two borehole seismometer arrays (KNW-BH and PFO-BH) have been established in the Southern California Batholith region of the San Jacinto Fault zone by the U.S. Geological Survey. The sites are within 0.4 km of Anza network surface stations and have three-component seismometers deployed at 300 m depth, at 150 m depth, and at the surface. Downhole horizontal seismometers can be oriented to an accuracy of about 5° using regional and near-regional initial P-wave particle motions. Shear waves recorded downhole at the KNW-BH indicate that the strong alignment of initial S-wave particle motions previously observed at the (surface) KNW Anza site (KNW-AZ) is not generated in the near-surface weathered layer. The KNW-BH surface instrument, which sits atop a highly weathered zone, displays a significantly different (≈ 20°) initial S-wave polarization direction from that observed downhole and at KNW-AZ, which is bolted to an outcrop. Although downhole initial shear-wave particle motion directions are consistent with a shear-wave splitting hypothesis, observations of orthogonally polarized slow shear waves are generally elusive, even in seismograms recorded at 300 m. A cross-correlation measure of the apparent relative velocities of Sfast and Sslow horizontally polarized S waves suggests shallow shear-wave anisotropy, consistent with the observed initial S-wave particle motion direction, of 2.3 ± 1.7 per cent between 300 and 150 m and 7.5 ± 3.5 per cent between 150 and 0 m.

scholarly journals Passive processing of active nodal seismic data: Estimation of V<sub>P</sub> / V<sub>S</sub>-ratios to characterize structure and hydrology of an alpine valley infill

2019 ◽  
Author(s):  
Michael Behm ◽  
Feng Cheng ◽  
Anna Patterson ◽  
Gerilyn Soreghan
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Velocity Ratio ◽  
Velocity Model ◽  
P Wave ◽  
Similar Data ◽  
S Wave ◽  
Alpine Valley ◽  
Active Source

Abstract. The advent of cable-free nodal arrays for conventional seismic reflection and refraction experiments is changing the acquisition style for active source surveys. Instead of triggering short recording windows for each shot, the nodes are continuously recording over the entire acquisition period from the first to the last shot. The main benefit is a significant increase in geometrical and logistical flexibility. As a by-product, a significant amount of continuous data might also be collected. These data can be analysed with passive seismic methods and therefore offer the possibility to complement subsurface characterization at marginal additional cost. We present data and results from a 2.4 km long active source profile which has been recently acquired in Western Colorado (US) to characterize the structure and sedimentary infill of an over-deepened alpine valley. We show how the leftover passive data from the active source acquisition can be processed towards a shear wave velocity model with seismic interferometry. The shear wave velocity model supports the structural interpretation of the active P-wave data, and the P-to-S-wave velocity ratio provides new insights into the nature and hydrological properties of the sedimentary infill. We discuss the benefits and limitations of our workflow and conclude with recommendations for acquisition and processing of similar data sets.

scholarly journals Advantages of Shear Wave Seismic in Morrow Sandstone Detection

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Paritosh Singh ◽  
Thomas Davis
Keyword(s):  
Shear Wave ◽  
Pure Shear ◽  
High Amplitude ◽  
Compressional Wave ◽  
Side Lobe ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
P Waves ◽  
Wave Data

The Upper Morrow sandstones in the western Anadarko Basin have been prolific oil producers for more than five decades. Detection of Morrow sandstones is a major problem in the exploration of new fields and the characterization of existing fields because they are often very thin and laterally discontinuous. Until recently compressional wave data have been the primary resource for mapping the lateral extent of Morrow sandstones. The success with compressional wave datasets is limited because the acoustic impedance contrast between the reservoir sandstones and the encasing shales is small. Here, we have performed full waveform modeling study to understand the Morrow sandstone signatures on compressional wave (P-wave), converted-wave (PS-wave) and pure shear wave (S-wave) gathers. The contrast in rigidity between the Morrow sandstone and surrounding shale causes a strong seismic expression on the S-wave data. Morrow sandstone shows a distinct high amplitude event in pure S-wave modeled gathers as compared to the weaker P- and PS-wave events. Modeling also helps in understanding the adverse effect of interbed multiples (due to shallow high velocity anhydrite layers) and side lobe interference effects at the Morrow level. Modeling tied with the field data demonstrates that S-waves are more robust than P-waves in detecting the Morrow sandstone reservoirs.

scholarly journals Passive processing of active nodal seismic data: estimation of <i>V</i><sub>P</sub>∕<i>V</i><sub>S</sub> ratios to characterize structure and hydrology of an alpine valley infill

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1337-1354 ◽  
Author(s):  
Michael Behm ◽  
Feng Cheng ◽  
Anna Patterson ◽  
Gerilyn S. Soreghan
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Velocity Ratio ◽  
Velocity Model ◽  
P Wave ◽  
S Wave ◽  
Alpine Valley ◽  
Active Source ◽  
Passive Seismic

Abstract. The advent of cable-free nodal arrays for conventional seismic reflection and refraction experiments is changing the acquisition style for active-source surveys. Instead of triggering short recording windows for each shot, the nodes are continuously recording over the entire acquisition period from the first to the last shot. The main benefit is a significant increase in geometrical and logistical flexibility. As a by-product, a significant amount of continuous data might also be collected. These data can be analyzed with passive seismic methods and therefore offer the possibility to complement subsurface characterization at marginal additional cost. We present data and results from a 2.4 km long active-source profile, which have recently been acquired in western Colorado (US) to characterize the structure and sedimentary infill of an over-deepened alpine valley. We show how the “leftover” passive data from the active-source acquisition can be processed towards a shear wave velocity model with seismic interferometry. The shear wave velocity model supports the structural interpretation of the active P-wave data, and the P-to-S-wave velocity ratio provides new insights into the nature and hydrological properties of the sedimentary infill. We discuss the benefits and limitations of our workflow and conclude with recommendations for the acquisition and processing of similar datasets.

scholarly journals Propriedades Sísmicas Anisotrópicas Derivadas da Orientação Cristalográfica Preferencial de Muscovita-Quartzo Milonitos

2007 ◽  
Vol 34 (2) ◽  
pp. 03
Author(s):  
LUIZ MORALES ◽  
LUÍS FERNANDES
Keyword(s):  
Shear Wave ◽  
Shear Waves ◽  
Seismic Wave Propagation ◽  
Preferred Orientation ◽  
Velocity Shear ◽  
P Wave ◽  
Low Velocity ◽  
P Waves ◽  
Seismic Properties ◽  
Wave Velocities

Seismic wave propagation in organized matter usually results in azimuthal variations of longitudinal waves (Pwaves), as well as the effect of birefringence in transversal waves (S-waves), which results in two orthogonal shear waves with contrasting velocities. In this paper we present the results of the anisotropic seismic properties of five samples of muscovitequartz mylonites collected in different parts of a fold in the Saas Fee region, Western Internal Alps. The P-wave velocities in these rocks varies from 5.73 to 6.32 km/s, whereas the high-velocity shear wave (S1) varies from 3.82 to 4.22 km/s and the low velocity (S2) from 3.73 to 4.09 km/s. The anisotropy in these rocks is relatively high and reaches values from 9.5% for P-waves, and almost 11% for shear wave splitting. Both anisotropy and propagation directions seem to be related to from the strong preferred orientation of quartz and muscovite but also depend of muscovite modal content within the different specimens. Development of preferred orientation of minerals destroys and disperses the single crystal seismic properties, which causes a decrease of wave velocities and a dispersion of propagation directions, of both compressional and shear waves. Since the preferred orientation of quartz and muscovite can be directly related to the main macroscopic structures in these rocks (foliation, lineation, and pole of foliation) and the anisotropic seismic properties are related to the preferred orientation, it is possible to determine the propagation directions in terms of these structures. Due to the relatively high muscovite content, many of the maximum propagation velocities are parallel/subparallel to the foliation and some parallel to the lineation of the reference frame. On the other hand, directions of minimum propagation cannot be directly related to the foliation pole. The presence of folds in the mid-to lower crust can exert changes in the propagation directions due to the foliation variation around such structures, mainly in the P-waves.

Direct shear-wave seismic survey in Sanhu area, Qaidam Basin, west China

2022 ◽  
Vol 41 (1) ◽  
pp. 47-53
Author(s):  
Zhiwen Deng ◽  
Rui Zhang ◽  
Liang Gou ◽  
Shaohua Zhang ◽  
Yuanyuan Yue ◽  
...  
Keyword(s):  
Shear Wave ◽  
Reservoir Characterization ◽  
Qaidam Basin ◽  
P Wave ◽  
Data Sets ◽  
Direct Shear ◽  
Subsurface Structure ◽  
S Wave ◽  
West China ◽  
Wave Data

The formation containing shallow gas clouds poses a major challenge for conventional P-wave seismic surveys in the Sanhu area, Qaidam Basin, west China, as it dramatically attenuates seismic P-waves, resulting in high uncertainty in the subsurface structure and complexity in reservoir characterization. To address this issue, we proposed a workflow of direct shear-wave seismic (S-S) surveys. This is because the shear wave is not significantly affected by the pore fluid. Our workflow includes acquisition, processing, and interpretation in calibration with conventional P-wave seismic data to obtain improved subsurface structure images and reservoir characterization. To procure a good S-wave seismic image, several key techniques were applied: (1) a newly developed S-wave vibrator, one of the most powerful such vibrators in the world, was used to send a strong S-wave into the subsurface; (2) the acquired 9C S-S data sets initially were rotated into SH-SH and SV-SV components and subsequently were rotated into fast and slow S-wave components; and (3) a surface-wave inversion technique was applied to obtain the near-surface shear-wave velocity, used for static correction. As expected, the S-wave data were not affected by the gas clouds. This allowed us to map the subsurface structures with stronger confidence than with the P-wave data. Such S-wave data materialize into similar frequency spectra as P-wave data with a better signal-to-noise ratio. Seismic attributes were also applied to the S-wave data sets. This resulted in clearly visible geologic features that were invisible in the P-wave data.

Numerical simulation of azimuthal acoustic logging in a borehole penetrating a rock formation boundary

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D283-D291 ◽  
Author(s):  
Peng Liu ◽  
Wenxiao Qiao ◽  
Xiaohua Che ◽  
Xiaodong Ju ◽  
Junqiang Lu ◽  
...  
Keyword(s):  
Domain Model ◽  
P Wave ◽  
S Wave ◽  
Angle Variation ◽  
P Waves ◽  
Acoustic Logging ◽  
S Waves ◽  
Rock Formation ◽  
Logging Tool ◽  
Difference Time

We have developed a new 3D acoustic logging tool (3DAC). To examine the azimuthal resolution of 3DAC, we have evaluated a 3D finite-difference time-domain model to simulate a case in which the borehole penetrated a rock formation boundary when the tool worked at the azimuthal-transmitting-azimuthal-receiving mode. The results indicated that there were two types of P-waves with different slowness in waveforms: the P-wave of the harder rock (P1) and the P-wave of the softer rock (P2). The P1-wave can be observed in each azimuthal receiver, but the P2-wave appears only in the azimuthal receivers toward the softer rock. When these two types of rock are both fast formations, two types of S-waves also exist, and they have better azimuthal sensitivity compared with P-waves. The S-wave of the harder rock (S1) appears only in receivers toward the harder rock, and the S-wave of the softer rock (S2) appears only in receivers toward the softer rock. A model was simulated in which the boundary between shale and sand penetrated the borehole but not the borehole axis. The P-wave of shale and the S-wave of sand are azimuthally sensitive to the azimuth angle variation of two formations. In addition, waveforms obtained from 3DAC working at the monopole-transmitting-azimuthal-receiving mode indicate that the corresponding P-waves and S-waves are azimuthally sensitive, too. Finally, we have developed a field example of 3DAC to support our simulation results: The azimuthal variation of the P-wave slowness was observed and can thus be used to reflect the azimuthal heterogeneity of formations.

scholarly journals Density-Depth Profile Determined by Seismic-Refraction Studies: Ice Stream B. West Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 198 ◽  
Author(s):  
S. Anandakrishnan
Keyword(s):  
Shear Wave ◽  
Seismic Velocity ◽  
Austral Summer ◽  
P Wave ◽  
S Wave ◽  
Data Logger ◽  
High Resolution Data ◽  
Ice Stream ◽  
Wave Profiles ◽  
Depth Curve

Detailed seismic short-refraction profiling was conducted on Ice Stream Β (UpB) during the 1983–84 austral summer. A new high-resolution data logger, developed at the University of Wisconsin, recorded both compressional- and shear-wave arrivals. We report here on P-wave and S-wave profiles recorded along a line parallel to the axis of the ice stream. Source-receiver separations up to 720 m yielded seismic velocity-depth curves to below the firn-ice transition zone (slightly greater than 30 m at UpB). For the compressional-wave profile, geophones were separated by 2.5 m, which yielded a velocity-depth curve with a granularity of ∼1 m. The corresponding density-depth curve agrees well with direct density measurements obtained from a core extracted nearby (Alley and Bentley 1988, this volume). Discontinuities in the velocity gradient do not appear at the “critical densities” as they did at Byrd Station, Antarctica, and elsewhere (Kohnen and Bentley 1973 , Robertson and Bentley 1975). Two shear-wave profiles were recorded, both with geophone spacings of 5 m, one with longitudinal polarization (SV) and the other with transverse polarization (SH). There is a marked difference in velocity between the SH and SV waves, particularly in the shallow firn. We suggest that a strong vertical shape-and-bonding fabric in the shallow firn, as observed in cores collected at UpB, would account for this disparity.

On the Green function of the Lord–Shulman thermoelasticity equations

2019 ◽  
Vol 220 (1) ◽  
pp. 393-403 ◽  
Author(s):  
Zhi-Wei Wang ◽  
Li-Yun Fu ◽  
Jia Wei ◽  
Wanting Hou ◽  
Jing Ba ◽  
...  
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Parabolic Type ◽  
Second Order ◽  
P Wave ◽  
Thermal Mode ◽  
S Wave ◽  
Order Tensor ◽  
P Waves ◽  
Thermal Conductivities

SUMMARY Thermoelasticity extends the classical elastic theory by coupling the fields of particle displacement and temperature. The classical theory of thermoelasticity, based on a parabolic-type heat-conduction equation, is characteristic of an unphysical behaviour of thermoelastic waves with discontinuities and infinite velocities as a function of frequency. A better physical system of equations incorporates a relaxation term into the heat equation; the equations predict three propagation modes, namely, a fast P wave (E wave), a slow thermal P wave (T wave), and a shear wave (S wave). We formulate a second-order tensor Green's function based on the Fourier transform of the thermodynamic equations. It is the displacement–temperature solution to a point (elastic or heat) source. The snapshots, obtained with the derived second-order tensor Green's function, show that the elastic and thermal P modes are dispersive and lossy, which is confirmed by a plane-wave analysis. These modes have similar characteristics of the fast and slow P waves of poroelasticity. Particularly, the thermal mode is diffusive at low thermal conductivities and becomes wave-like for high thermal conductivities.

Sign in / Sign up

Export Citation Format

Share Document