Text S2. Inverted Vs model using the Chen
et al. (2016) starting
model
The output Vs model using the Chen et al. (2016) starting model is
presented in Figure S2, as a comparison to the result using the Herrmann
(2013) model. Velocities in the lower crust (3.5 km/s to 5.1 km/s) vary
over a larger range than those determined using the Herrmann (2013)
starting model, and the difference in the upper limit is more
significant than the difference in the lower limit. These results are
close to the results obtained by Chen et al. (2016) for the crustal
velocity values. Velocities in the uppermost mantle (50-150 km depths)
vary between 4.29 km/s and 4.96 km/s, which is close to the result
obtained using the Herrmann (2013) model. The above comparison shows
that in the resolved Vs model, velocities in the lower crust are more
sensitive to the starting model than velocities in the mantle.
The distributions of high- and low-velocity anomalies are consistent
with the result obtained with the Herrmann (2013) model, although the
magnitudes of low-velocity anomalies appear more significant in this
model than the results obtained with the Herrmann (2013) model. On the
24 km and 36 km slices, low-velocity anomalies characterize the Ozark
uplift (labeled J), the central Illinois Basin (labeled K), and the
Rough Creek Graben (labeled L). Since the magnitudes of these
low-velocity anomalies are too prominent, they are considered an
artifact introduced by the starting model.