Figure 1. The phase diagram of mineralogy and thermal
gradient of top 1000 km of Earth’s mantle. The mantle transition zone is marked
by two phase changes at 410 and 660km discontinuities. The 410 km discontinuity
is caused by a phase change from olivine to wadsleyite. The 660 km discontinuity
is caused by a phase change from ringwoodite to perovskite and manesiowustite. (Bellini et al., 2013)
Figure 2. The
minerals in mantle transition zone are aligned by the subducting flow. The
mineral alignment can produce seismic anisotropy in the mantle transition zone.
Figure 3. The ray path of SS phase and SS precursors. (A)
The whole ray path of SS phase and SS precursor with epicentral distance 125
degree and 180 degree. (B) The ray path beneath the SS bounce points. The
polarization of SV wave and SH wave is shown as blue arrows and red arrows
respectively. This study will only use SH wave to look at the azimuthal
anisotropy.
Figure 4. The illustration of shear wave splitting in anisotropic
materials. Shear wave can be split into two orthogonally polarized waves (blue
and red) after traveling through anisotropic minerals. (Ed Garnero, http://garnero.asu.edu/research_images/images_anisotropy.html)
Figure 5. A map of earthquake event and station
locations. The red circles are earthquakes and blue triangles are stations.
Figure 6. The map of SS bounce point locations and azimuths.
The azimuths of bounce points are plotted as different colors. The black boxes
are the locations with enough bounce point density and azimuthal coverage.
Figure 7. The
S410S travel time (top) and S660S travel time (bottom) are plotted
against azimuth. The grey circles and error bars are the travel time
measurements and uncertainties from individual azimuthal bins. The red circles
and error bars are the average of individual measurements within every 30 degree.
Figure 8. The differential
travel time between S410S and S660S are plotted against azimuth. The grey
circles and error bars are the travel time measurements and uncertainties from
individual azimuthal bins. The red circles and error bars are the average of
individual measurements within every 30
degree.
