Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale fundamental-
mode Rayleigh-wave group-velocity tomography
Item Type Article
Authors Tang, Zheng;Mai, Paul Martin;Chang, Sung-Joon;Zahran, Hani Citation Tang Z, Mai PM, Chang S-J, Zahran H (2018) Evidence for crustal
low shear-wave speed in western Saudi Arabia from multi-scale fundamental-mode Rayleigh-wave group-velocity tomography.
Earth and Planetary Science Letters 495: 24–37. Available: http://
dx.doi.org/10.1016/j.epsl.2018.05.011.
Eprint version Post-print
DOI 10.1016/j.epsl.2018.05.011
Publisher Elsevier BV
Journal Earth and Planetary Science Letters
Rights NOTICE: this is the author’s version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document.
Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Earth and Planetary Science Letters, [495, 1 August 2018] DOI:
10.1016/j.epsl.2018.05.011. © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://
creativecommons.org/licenses/by-nc-nd/4.0/
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Link to Item http://hdl.handle.net/10754/627909
1 Supporting Information
1
“Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale 2
fundamental-mode Rayleigh-wave group-velocity tomography”
3 4
Zheng Tang1, P. Martin Mai1, Sung-Joon Chang2, and Hani Zahran3 5
1King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia 6
2Kangwon National University (KNU), Chuncheon, South Korea 7
3Saudi Geological Survey (SGS), Jeddah, Saudi Arabia 8
9
We have attached an electronic supplement (a compressed file) that includes the Rayleigh-wave 10
group-velocity tomography results (i.e., maps of group-velocities at each period between 8 and 11
40 s, in ASCII format) and the shear-wave velocity inversion results (i.e., maps of S-velocities 12
for different depths within the study region, in ASCII format).
13
14
Figure S1. Ray-density maps shown as the number of ray-paths crossing each 0.8° x 0.8° cell at 15
periods of 8 – 40 s.
16
20˚E 30˚E 40˚E 50˚E 60˚E
10˚N 20˚N 30˚N 40˚N
a.
T = 8 s
20˚E 30˚E 40˚E 50˚E 60˚E
b.
T = 10 s
20˚E 30˚E 40˚E 50˚E 60˚E
10˚N 20˚N 30˚N 40˚N
c.
T = 15 s
10˚N 20˚N 30˚N 40˚N
d.
T = 20 s
20˚E 30˚E 40˚E 50˚E 60˚E
e.
T = 25 s
20˚E 30˚E 40˚E 50˚E 60˚E
10˚N 20˚N 30˚N 40˚N
f.
T = 30 s
20˚E 30˚E 40˚E 50˚E 60˚E
10˚N 10˚N
20˚N 20˚N
30˚N 30˚N
40˚N 40˚N
g.
T = 40 s
0 50 100 150 200
Ray Density
3 17
Figure S2. Histograms of the 20-s Rayleigh-wave group-velocity measurements for the four ray- 18
path clusters (Fig. 2): (a) cluster 1 contains the rays from northwestern directions (Fig. 2; red 19
ray-paths); (b) cluster 2 includes the rays from north-northeastern directions (green ray-paths);
20
(c) cluster 3 consists of the rays primarily from the east (cyan-colored); (d) cluster 4 comprises 21
the rays from earthquakes in the south-southeast (Red Sea, Gulf of Aden and Arabian Sea; violet 22
ray-paths). Blue lines indicate the mean and the 3-𝛔 limits for each group, respectively. Note that 23
the distribution of measured group-velocities is nearly normal distribution for all four clusters.
24
25
Figure S3. Trade-off curves (a) between root-mean-square (RMS) misfit and model roughness 26
(1/s), and (b) between RMS misfit and model variance (km/s)2 for 10 s and 30 s period. The 27
curves help identifying the optimal balance between RMS and model roughness, and between 28
RMS and model variance. Here, we choose smoothness parameter η = 4 and damping value ε = 29
1.
30
5 31
Figure S4. Checkerboard tests for Rayleigh-wave group-velocity tomography at periods of 8 – 40 32
s. A 2.5° x 2.5° initial checkerboard pattern with imposed ±0.8 km/s group-velocity anomalies is 33
applied. The images show the degradation in resolution at the periphery of the modeled domain 34
as well as the period-dependence of resolution, owing to the ray density (Fig. S1).
35
36
Figure S5. Same as Figure S4, but with a 2.5° x 2.5° initial checkerboard pattern with imposed 37
anomalies of ±0.4 km/s.
38
7 39
Figure S6. Checkerboard tests for Rayleigh-wave group-velocity tomography at periods of 8 – 40 40
s for the Cenozoic lava fields in the Arabian Shield, applying a 1.5° x 1.5° checkerboard pattern 41
with anomalies of ±0.4 km/s.
42
43
Figure S7. AK135 velocity model (black) versus our starting model (violet). Note the differences 44
in the crustal levels (0 – 50 km). For the mantle levels (below 50 km), both initial 1-D structures 45
are identical.
46 2.5
3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
2.5 3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
a. 2.5
3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
2.5 3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
b.
−220
−200
−180
−160
−140
−120
−100
−80
−60
−40
−20 0
Depth (km)
2.5 3.0 3.5 4.0 4.5 5.0
Vs (km/s) a.
Lat 24.2°
Lon 40.0°
−220
−200
−180
−160
−140
−120
−100
−80
−60
−40
−20 0
Depth (km)
2.5 3.0 3.5 4.0 4.5 5.0
Vs (km/s)
9 47
Figure S8. 1-D shear-wave velocity inversions at nodes - (a) 24.2° N, 40.0° E in the Arabian 48
shield; (b) 28.2° N, 48.0° E in the Arabian platform. Both the inverted models using our starting 49
model (red lines) and the inverted results using the AK135 model (blue lines) are displayed. The 50
green lines show the models at station RHT01 (24.27° N, 39.81° E) and KFJS (28.19° N, 47.94°
51
E) from the joint inversion of Tang et al. (2016).
52
2.5 3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
2.5 3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
a. 2.5
3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
2.5 3.0 3.5 4.0
U (km/s)
0 20 40 60 80 100 120 140
Period (s)
b.
−220
−200
−180
−160
−140
−120
−100
−80
−60
−40
−20 0
Depth (km)
2.5 3.0 3.5 4.0 4.5 5.0
Vs (km/s) a.
Lat 24.2°
Lon 40.0°
−220
−200
−180
−160
−140
−120
−100
−80
−60
−40
−20 0
Depth (km)
2.5 3.0 3.5 4.0 4.5 5.0
Vs (km/s) b.
Lat 28.2°
Lon 48.0°
53
Figure S9. Horizontal slices of shear-velocity anomalies in the crust (0 – 45 km) using the 54
AK135 Earth models as starting model for inversion. Comparing with Fig. 6, we find minor 55
35˚E 40˚E 45˚E 50˚E
15˚N 20˚N 25˚N 30˚N 35˚N
a.
0−5 km 3.10 km/s
35˚E 40˚E 45˚E 50˚E
b.
5−10 km 3.20 km/s
35˚E 40˚E 45˚E 50˚E
15˚N 20˚N 25˚N 30˚N 35˚N
c.
10−15 km 3.45 km/s
15˚N 20˚N 25˚N 30˚N 35˚N
d.
15−20 km 3.50 km/s
e.
20−25 km 3.90 km/s
15˚N 20˚N 25˚N 30˚N 35˚N
f.
25−30 km 3.85 km/s
35˚E 40˚E 45˚E 50˚E 15˚N
20˚N 25˚N 30˚N 35˚N
g.
30−35 km 3.75 km/s
35˚E 40˚E 45˚E 50˚E
−12 −8 −4 0 4 8 12
dVs/Vs (%)
h.
35−40 km 4.35 km/s
35˚E 40˚E 45˚E 50˚E 15˚N 20˚N 25˚N 30˚N 35˚N
i.
40−45 km 4.35 km/s
11 58
Figure S10. Horizontal slices of shear-velocity anomalies at the crustal levels (0 - 45 km) below 59
the Cenozoic volcanic regions, based on the starting Earth model AK135. Like in Figure S7, the 60
spatial patterns of velocity anomalies remain unaltered, however, the reference shear-wave 61
velocities in each layer are changed.
62
38˚E 40˚E 42˚E
20˚N 22˚N 24˚N 26˚N 28˚N
A A’
B B’
C C’
a.
0−5 km 3.10 km/s
38˚E 40˚E 42˚E
b.
5−10 km 3.20 km/s
38˚E 40˚E 42˚E
20˚N 22˚N 24˚N 26˚N 28˚N
c.
10−15 km 3.45 km/s
20˚N 22˚N 24˚N 26˚N 28˚N
d.
15−20 km 3.50 km/s
e.
20−25 km 3.90 km/s
20˚N 22˚N 24˚N 26˚N 28˚N
f.
25−30 km 3.85 km/s
38˚E 40˚E 42˚E
20˚N 22˚N 24˚N 26˚N 28˚N
g.
30−35 km 3.75 km/s
38˚E 40˚E 42˚E
−10−8−6−4−2 0 2 4 6 8 10
dVs/Vs (%)
h.
35−40 km 4.35 km/s
38˚E 40˚E 42˚E
20˚N 22˚N 24˚N 26˚N 28˚N
i.
40−45 km 4.35 km/s
