Auxiliary Material for
Sub-slab anisotropy beneath the Sumatra and circum-Pacific subduction zones from
source-side shear wave splitting observations
Colton Lynner and Maureen D. Long
(Yale University Department of Geology and Geophysics, New Haven, CT)
[Geochemistry, Geophysics, Geosystems]
Introduction
Data tables containing the splitting patterns and parameters of the seismic stations
examined in the source-side shear wave splitting studies of the Izu-Bonin-JapanKurile, Ryukyu, Central America, Alaska-Aleutians, and Sumatra subduction zones,
the source-side splitting measurements (both fast direction,, and delay time, t)
made in each region along with corresponding 2 error estimates, an example of the
receiver-side station correction technique, plots of null splits recorded in each
region as well as a plot of fast measured splitting parameters versus various
subduction parameters are provided. The SK(K)S shear wave splitting pattern, the
receiver-side correction (if a station is suitable for use with the source-side splitting
technique), and the correction for stations with misaligned horizontal components
(should a correction be necessary) provided for every station examined in this study
can be found in table “SupplementalTable1.xlsx”.
1. SupplementalTable1.xlsx. Information on whether a station is appropriate for use
with the source-side splitting technique and their associated receiver-side
corrections.
1.1 Column Station, name of seismic station
1.2 Column Network, seismic network to which a station belongs
1.3 Column Lat, latitude of seismic station location
1.4 Column Long, longitude of seismic station location
1.5 Column Splitting Type, brief characterization of observed SK(K)S splitting, only
those with Simple Splitting or Null characterizations can be used with the sourceside splitting technique
1.6 Column Correction, anisotropy beneath a seismic station, both fast direction
(phi) and delay time, reported phi/dt.
1.7 Column Misalignment, misalignment of seismic stations should there be a
misalignment, degrees
2. SupplementalTable2.xlsx. Source-side shear wave splitting measurements made
in this study separated by shallow (<250 km) and deep (<250 km) event depths.
2.1 Column Station, seismic station name where a measurement was made
2.2 Column Subduction Zone, subduction zone where an event originated
2.3 Column Lat, latitude of an event
2.4 Column Long, longitude of an event
2.5 Column Depth, depth of an event
2.6 Column Baz, backazimuth of an event relative to the station, degrees
2.7 Column Relative Azimuth, azimuth of the downgoing ray relative to a trench
normal orientation in the up-dip direction, degrees
2.8 Column Dist, epicentral distance between an event and station, degrees
2.9 Column Phi-, lower bound of the 2 error estimate of measured fast direction,
degrees
2.10 Column Phi, measured fast direction, degrees
2.11 Column Phi+, upper bound of the 2 error estimate of measured fast direction,
degrees
2.12 Column dt-, lower bound of the 2 error estimate of measured delay time,
seconds
2.13 Column dt, measured delay time, seconds
2.14 Column dt+, upper bound of the 2 error estimate of measured delay time,
seconds
3. FigureS1.pdf, Example of the receiver-side correction procedure for a Japan
region event recorded at seismic station SKAG (receiver-side splitting parameters:
1.0 sec delay time, -23 fast direction). (Left panels) Horizontal components for the
initial (before receiver-side anisotropy correction, top), rotated (to the observed
station fast direction, middle), and station anisotropy corrected (bottom)
waveforms. (Right panels) Particle motion of the initial (before station correction,
top) and station corrected (middle) waveforms as well as the source-side splitting
parameter error surface (after removal of receiver-side anisotropy, bottom) for the
measured event.
4. FigureS2.pdf, Null splitting results from the Japan-Ryukyu region. Circles are
plotted at the event location. The bars correspond to the two possible orientations,
either the polarization of the fast or the slow directions of anisotropy, of the null
split ray calculated from the initial polarization of the incoming S wave. Nulls are
plotted in relation to their orientation in the sub-slab mantle, not in reference to the
seismic station at which they were recorded.
5. FigureS3.pdf, Null splitting results from the Alaska-Aleutians region. Circles are
plotted at the event location. The bars correspond to the two possible orientations,
either the polarization of the fast or the slow directions of anisotropy, of the null
split ray calculated from the initial polarization of the incoming S wave. Nulls are
plotted in relation to their orientation in the sub-slab mantle, not in reference to the
seismic station at which they were recorded.
6. FigureS4.pdf, Null splitting results from Central America. Circles are
plotted at the event location. The bars correspond to the two possible orientations,
either the polarization of the fast or the slow directions of anisotropy, of
the null split ray calculated from the initial polarization of the incoming S wave.
Nulls are plotted in relation to their orientation in the sub-slab mantle, not in
reference to the seismic station at which they were recorded.
7. FigureS5.pdf, Null splitting results of the source-side splitting study beneath
Sumatra. Circles are plotted at the event location. The bars correspond to the two
possible orientations, either the polarization of the fast or the slow directions of
anisotropy, of the null split ray calculated from the initial polarization of the
incoming S wave. Nulls are plotted in relation to their orientation in the sub-slab
mantle.
8. FigureS6.pdf, Plots of various parameters that may influence patterns of sub-slab
anisotropy against relative observed fast directions. Blue symbols correspond to the
deviation between measured fast directions and the local trench strike, while red
symbols represent the measured fast directions relative to the local motion of the
subducting slab. Shown are plots of relative fast direction versus event depth (A),
the velocity of the subducting plate [DeMets et al., 2010] (B), the incidence angle of
the downgoing ray (C), takeoff angle (the angle between slab dip and the incidence
of the downgoing ray) (D), slab dip (at a depth of 125 km) [Lallemand et al., 2005]
(E), the azimuth of the downgoing ray relative to a trench normal orientation in the
up-dip direction (F), and the length of the trench (labels are provided for each
trench) (G).