Journal of Geophysical Research – Solid Earth
Supporting Information for
Crustal Imprints of Precambrian Orogenesis in Western Laurentia
Yunfeng Chena, Yu Jeffrey Gua,* , Ramin M. H. Dokhta, Mauricio D. Sacchia
aDepartment
of Physics, University of Alberta, Edmonton, AB, Canada, T6G2E1
Contents of this file
Figures S1 to S2
Introduction
Aside from two earlier tests (see manuscript section 4.4) that evaluate the sensitivity of the
receiver functions (RFs) to the low velocity structure, we conducted a third synthetic test to
investigate the resolvability of the HVZ and, most importantly, to inquire if an artificial LVZ will
occur in response to an input high velocity structure. We involved two types of HVZ to our
simulation. The first model contains an 8 km thick high velocity layer with a constant velocity of
~3.7 km/sec in the upper crust (blue line in Figure S1(b)). We then generate the synthetic RFs
(noise added), which are subsequently inverted for the shear velocity structure. The output
model (red line in Figure S1(b)) properly recovers the HVZ. The deviations of the model
(inversion artifacts) by ~0.2 km/sec are only present at shallower depth above the HVZ, whereas
the gradational crust below HVZ is well resolved without generating an artificial LVZ.
A model with a constant low velocity layer (Figure S1(d)) was also tested, which allows a
direct comparison of the resolving power of RF pertaining to the existing HVZ and LVZ. In the
presence of LVZ, the inversion produces significant artificial HVZ, which is ~0.35 km/sec faster
than the input model, atop the LVZ. The strength of LVZ is also slightly overestimated by ~0.1
km/sec (see the output model (red) in Figure S1(d)).
In second test, the HVZ is placed at middle crustal depth by adding 10% positive velocity
perturbation to an otherwise gradational crust (Figure S2(b)). The inversion procedures and
parameters are the same as those of test one. In this test, the output model (red line in Figure
S2(b)) shows a good recovery of the HVZ. For comparison, a model with velocity 10% lower than
the gradational crust (Figure S2(d)) is constructed. The inversion properly estimates the size of
the LVZ but, again, introduced an artificial high velocity lid above the LVZ (see Figure S4(d)).
Summarizing the results from the aforementioned synthetic tests, we conclude that 1) RF
has different resolving powers regarding various structures, 2) the HVZ can be more easily
imaged than the LVZ, which can be partially attributed to the more severe wave-front healing
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effect caused by the low velocity anomalies and 3) the presence of a HVZ should not cause an
artificial LVZ in the recovered model.
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Figure S1. Synthetic tests evaluating the inversion artifacts. (a) The upper and lower
panels show the waveform fitting results of the high and low frequency RFs, respectively. The
blue and red lines represent the respective observed and inverted RFs. (b) The input model with
HVZ of constant velocity (blue). The optimal model recovered from the inversion is shown in
red. (c) The waveform fitting results for the synthetic test with a LVZ of constant velocity. (d)
The input (blue) and recovered models (red).
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Figure S2. Synthetic tests evaluating the inversion artifacts. (a) The upper and lower panels
show the waveform fitting results of the high and low frequency RFs, respectively. The blue and
red lines represent the respective observed and inverted RFs. (b) The model with a high velocity
upper crust that is 10% faster than the gradational crust. The optimal recovered model is shown
in red. (c) The waveform fitting results for the model with a low velocity layer that is 10% slower
than the gradational crust. (d) The input (blue) and recovered models (red).
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