4.1 Strength of Anisotropy
“The strength of anisotropy is calculated by the “kern and Richter” formula which gives the magnitude anisotropy k= (Vmax –V min)/Vmean, where Vmax and Vmin are maximum and minimum velocity. For P wave in the olivine crystal Vmax and Vmax are 9.89 and 7.72km/s respectively, so strength of anisotropy is 25%. For S wave k= 22% for Vmax and Vmin are 5.53 and 4.42 km/s respectively” [Seth stein 2003]. This anisotropy is the intrinsic anisotropy of the material defined as the difference between the maximum and the minimum velocity of the medium. However the percentage anisotropy in terms of the splitting parameters is different from the intrinsic anisotropy.
Percent anisotropy = 200 (Vs1 – Vs2)/ (Vs1+ Vs2) where Vs1 and …show more content…
“Two deformation types are Important in upper mantle conditions: diffusion creep and dislocation creep. Diffusion creep is solid-state diffusion between grain boundaries or across a crystal lattice. Preferred mineral orientation is not developed and thus the deformed material is isotropic. Diffusion creep occurs at relatively low stress, small grain size, or both: the strain rate increases linearly with stress but decreases significantly with grain size. Dislocation creep is the motion of crystalline dislocations within grains; it causes preferred mineral orientation and therefore anisotropy. It occurs with high stress, large grains size, or both; the strain rate increases nonlinearly with stress and is insensitive to grain size” [Savage.M.K (1999)]. Other forms of deformation may yield different anisotropic properties. Uniaxial compression tends to orient the slip plane normal to the compression …show more content…
These average values contribute from 0.04 to 0.2 s to the splitting. However, some stations located above faults may record as much as 0.5 s splitting. At pressures greater than 200-300 MPa, corresponding to 10-15 km depth, much of the anisotropy measured in the laboratory disappears primarily due to closure of crack. [Savage.M.K (1999)] So any anisotropy below this depth can be due to other process such as preferred orientation of minerals by the ductile flow of lower crust. For teleseismic shear wave splitting, crustal rocks may contribute little to splitting because foliation planes within the crust are usually horizontal, and with vertical propagation of teleseismic phases the splitting is expected to be small. The presence of 10 km thick mica schist can cause a splitting up to 1 second [Arun Singh
“The strength of anisotropy is calculated by the “kern and Richter” formula which gives the magnitude anisotropy k= (Vmax –V min)/Vmean, where Vmax and Vmin are maximum and minimum velocity. For P wave in the olivine crystal Vmax and Vmax are 9.89 and 7.72km/s respectively, so strength of anisotropy is 25%. For S wave k= 22% for Vmax and Vmin are 5.53 and 4.42 km/s respectively” [Seth stein 2003]. This anisotropy is the intrinsic anisotropy of the material defined as the difference between the maximum and the minimum velocity of the medium. However the percentage anisotropy in terms of the splitting parameters is different from the intrinsic anisotropy.
Percent anisotropy = 200 (Vs1 – Vs2)/ (Vs1+ Vs2) where Vs1 and …show more content…
“Two deformation types are Important in upper mantle conditions: diffusion creep and dislocation creep. Diffusion creep is solid-state diffusion between grain boundaries or across a crystal lattice. Preferred mineral orientation is not developed and thus the deformed material is isotropic. Diffusion creep occurs at relatively low stress, small grain size, or both: the strain rate increases linearly with stress but decreases significantly with grain size. Dislocation creep is the motion of crystalline dislocations within grains; it causes preferred mineral orientation and therefore anisotropy. It occurs with high stress, large grains size, or both; the strain rate increases nonlinearly with stress and is insensitive to grain size” [Savage.M.K (1999)]. Other forms of deformation may yield different anisotropic properties. Uniaxial compression tends to orient the slip plane normal to the compression …show more content…
These average values contribute from 0.04 to 0.2 s to the splitting. However, some stations located above faults may record as much as 0.5 s splitting. At pressures greater than 200-300 MPa, corresponding to 10-15 km depth, much of the anisotropy measured in the laboratory disappears primarily due to closure of crack. [Savage.M.K (1999)] So any anisotropy below this depth can be due to other process such as preferred orientation of minerals by the ductile flow of lower crust. For teleseismic shear wave splitting, crustal rocks may contribute little to splitting because foliation planes within the crust are usually horizontal, and with vertical propagation of teleseismic phases the splitting is expected to be small. The presence of 10 km thick mica schist can cause a splitting up to 1 second [Arun Singh