On: “Field measurements of azimuthal anistropy: First 60 meters, San Francisco Bay area, CA, and estimation of the horizontal stresses' ratio from Vs1/Vs2” by Heloise Bloxsom Lynn (June 1991 GEOPHYSICS, p. 822–832)

Geophysics ◽  
1992 ◽  
Vol 57 (4) ◽  
pp. 653-655
Author(s):  
D. F. Winterstein
Keyword(s):  
San Francisco ◽  
San Francisco Bay ◽  
San Francisco Bay Area ◽  
Field Measurements ◽  
Azimuthal Anisotropy ◽  
S Wave ◽  
Near Surface ◽  
Inappropriate Use ◽  
Bay Area ◽  
Surface Materials

What I would like to discuss has little to do with the content of Heloise Lynn’s paper, which beautifully illustrates S‐wave birefringence in near‐surface materials. My concern is with the terminology. Inappropriate use of the term azimuthal anisotropy has become so prevalent in both oral and written presentations that someone needs to point out clearly and in detail why such usage is ill‐advised. My comments, thus, while triggered by the usage of this paper, are for an audience that includes many besides the paper’s author.

Field measurements of azimuthal anisotropy: First 60 meters, San Francisco Bay area, CA, and estimation of the horizontal stresses’ ratio from Vs1/Vs2

Geophysics ◽  
1991 ◽  
Vol 56 (6) ◽  
pp. 822-832 ◽  
Author(s):  
Heloise Bloxsom Lynn
Keyword(s):  
San Francisco ◽  
Field Experiments ◽  
San Francisco Bay Area ◽  
Field Measurements ◽  
Azimuthal Anisotropy ◽  
Fabric Anisotropy ◽  
Near Surface ◽  
Fault Systems ◽  
Bay Area ◽  
San Andreas

[Formula: see text], Q) of near‐surface strata. The azimuthal anisotropy revealed in these field experiments is the result of a combination of circumstances: unequal horizontal stresses (the data were collected near the center of the San Andreas and associated fault systems), fabric anisotropy introduced by the depositional agent, and stress‐aligned fluid‐filled microcracks, cracks, or pore spaces.

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