Shear‐wave splitting measurements from multishot VSP data

1988 ◽  
Author(s):  
L. Nicoietis ◽  
C. Client ◽  
R. Lefeuvre
Keyword(s):  
Shear Wave ◽  
Shear Wave Splitting ◽  
Wave Splitting ◽  
Vsp Data

Estimating interval shear-wave splitting from multicomponent virtual shear check shots

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. A39-A43 ◽  
Author(s):  
Andrey Bakulin ◽  
Albena Mateeva
Keyword(s):  
Shear Wave ◽  
Shear Wave Splitting ◽  
Azimuthal Anisotropy ◽  
Data Set ◽  
Vertical Seismic Profiling ◽  
Wave Splitting ◽  
Vsp Data ◽  
Classic Approach ◽  
A New Technique

Measuring shear-wave splitting from vertical seismic profiling (VSP) data can benefit fracture and stress characterization as well as seismic processing and interpretation. The classic approach to measuring azimuthal anisotropy at depth involves layer stripping. Its inherent weakness is the need to measure and undo overburden effects before arriving at an anisotropy estimate at depth. That task is challenging when the overburden is complex and varies quickly with depth. Moreover, VSP receivers are rarely present all the way from the surface to the target. That necessitates the use of simplistic assumptions about the uninstrumented part of the overburden that limit the quality of the result. We propose a new technique for measuring shear-wave splitting at depth that does not require any knowledge of the overburden. It is based on a multicomponent version of the virtual source method in which each two-component (2-C) VSP receiver is turned into a 2-C shear source and recorded at deeper geophones. The resulting virtual data set is affected only by the properties of the medium between the receivers. A simple Alford rotation transforms the data set into fast and slow shear virtual check shots from which shear-wave splitting can be measured easily and accurately under arbitrarily complex overburden.

Interpreting data matrix asymmetry in near‐offset, shear‐wave VSP data

Geophysics ◽  
1994 ◽  
Vol 59 (2) ◽  
pp. 176-191 ◽  
Author(s):  
Colin MacBeth ◽  
Xinwu Zeng ◽  
Gareth S. Yardley ◽  
Stuart Crampin
Keyword(s):  
Shear Wave ◽  
Shear Wave Splitting ◽  
Synthetic Seismograms ◽  
Data Matrix ◽  
Depth Range ◽  
Wave Polarization ◽  
Polarization Azimuth ◽  
Polarization Change ◽  
Wave Splitting ◽  
Vsp Data

Poor experimental control in shear‐wave VSPs may contribute to unreliable estimates of shear‐wave splitting and possible misinterpretation of the medium anisotropy. To avoid this, the acquisition and processing of multicomponent shear‐wave data needs special care and attention. Measurement of asymmetry in the recorded data matrix using singular‐value decomposition (SVD) provides a useful way of examining possible acquisition inaccuracies and may help guide data conditioning and interpretation to ensure more reliable estimates of shear‐wave polarization azimuth. Three examples demonstrate how variations in shear‐wave polarization and acquisition inaccuracies affect the SVD results in different ways. In the first example, analysis of synthetic seismograms with known depth changes in the polarization azimuth show how these may be detected. In the second example, a known source re‐orientation and polarity reversal is detected by applying SVD to near‐offset, shear‐wave VSP data, recorded in the Romashkino field, Tatar Republic. Additional information on a polarization change in the overburden is also obtained by comparing the SVD results with those for full‐wave synthetic seismograms. The polarization azimuth changes from N160°E in the overburden to N117°E within the VSP depth range. Most of the shear‐wave splitting is built up over the VSP depth range. The final example is a near‐offset, shear‐wave VSP data set from Lost Hills, California. Here, most of the shear‐wave splitting is in the shallow layers before the VSP depth range. SVD revealed a known correction for horizontal reorientation of the sources, but also exhibited results with a distinct oscillatory behavior. Stripping the overburden effects reduces but does not eliminate these oscillations. There appears to be a polarization change from N45°E in the overburden to N125°E in the VSP section. The details in these examples would be difficult to detect by visual inspection of the seismograms or polarization diagrams. Results from these preliminary analyses are encouraging and suggest that it may be possible to routinely use this, or a similar technique, to resolve changes in the subsurface anisotropy from multicomponent experiments where acquisition has not been carefully controlled.

Analysis of shear wave splitting anisotropy in the Tres Virgenes Volcanic Complex, Baja California Sur, Mexico

Geothermics ◽  
2021 ◽  
Vol 94 ◽  
pp. 102115
Author(s):  
F. Chacón-Hernández ◽  
F.R. Zúñiga ◽  
J.O. Campos-Enríquez ◽  
J. Lermo-Samaniego ◽  
N. Jiménez-Méndez
Keyword(s):  
Shear Wave ◽  
Baja California ◽  
Shear Wave Splitting ◽  
Volcanic Complex ◽  
Baja California Sur ◽  
Wave Splitting
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