SH-SV Polarization Anisotropy: Isotropic Interpretation of Experimentally Measured Love and Rayleigh Wave Phase Velocities and Amplitude Attenuations

Session: Advances in Seismic Imaging of Earth’s Mantle and Core and Implications for Convective Processes [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

For perfectly elastic earth models composed of thick, low contrast layers, researchers are often unable to find a single isotropic model whose computed phase velocities fit the observed fundamental mode Love and Rayleigh waves. While it has been shown that a single isotropic model can possibly fit both the Love and Rayleigh phase-velocity data if thin, high contrast layers are allowed in those models; instead, many authors use body-wave, velocity anisotropy in the model. Here, we attempt to complete and extend the verification of these successful isotropic models, but with realistic, anelastic layers.

Using very simple structural models with three thin high contrast layers superposed: an “olivine” LVZ at 152 km of depth, a “lower-crustal” LVZ at the Moho depth and a “granitic” LVZ at the Conrad-discontinuity depth, we found so many solutions, that we were forced to add the Love and Rayleigh wave amplitude-attenuation data in order to restrict the huge volume of isotropic solutions. This yielded a successful model for the central U.S.: (1) a preferred (idealized) physical model for the “olivine” LVZ: a building-block model of the crystal aggregate with a 3-D laminate of basalt-melt film separating crystals over a 0.1 m vertical region centered at the 152 km depth, i.e. a horizontal, lubricated interface with an average melt fraction of 0.001 %; and, appropriately modified, (2) a like idealization for the "lower-crustal" LVZ centered at a depth of 38 km.

This completely isotropic mechanism: (1) successfully explains (removes) the apparent “discrepancy” between measured Love and Rayleigh wave phase velocities in the central U.S.; (2) contains a corrected form of the Gutenberg LVZ in the asthenosphere, with a mobile interface replacing the usual, thick, static LVZ layer; and also (3) contains a plausible basis for the continental portion of drift, or plate motion.

Presenting Author: Gyanendra Gurung

Authors