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Supporting information for
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Investigating multiple fault rupture at the Salar del Carmen segment of the Atacama Fault System
(northern Chile): Fault scarp morphology and knickpoint analysis
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Authors
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1.
Oktawian Ewiak (corresponding author)
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Department of Geodynamics
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GeoForschungsZentrum Potsdam
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Telegrafenberg
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D-14473 Potsdam
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oewiak@gfz-potsdam.de
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2.
Pia Victor
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Department of Geodynamics
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GeoForschungsZentrum Potsdam
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Telegrafenberg
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D-14473 Potsdam
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pvictor@gfz-potsdam.de
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3.
Onno Oncken
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Department of Geodynamics
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GeoForschungsZentrum Potsdam
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Telegrafenberg
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D-14473 Potsdam
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oncken@gfz-potsdam.de
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Journal:
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Tectonics (2015)
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Supporting information outline
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1. Introduction
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2. Sensitivity tests
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3. Calculation of synthetic SRL
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4. File descriptors and supplementary figure captions
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1. Introduction
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The supplementary material to this article contains two short text passages describing a) the
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sensitivity tests carried out to examine the effects of varying parameters on the routine for
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calculation of gradient along profile, and to estimate an age threshold up to which our approach
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reliably detects breaks in slope in the analyzed profiles, and b) the calculation of synthetic rupture
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lengths from previously derived paleomagnitudes. These descriptions are provided in the
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paragraphs below.
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2. Sensitivity tests
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To examine the effects of varying parameters on the routine for calculation of gradient along
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profile, and to estimate an age threshold up to which our approach reliably detects breaks in slope
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in the analyzed profiles, we conducted a series of tests. For this purpose, we created synthetic
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profiles with a length of 100 m. We varied the initial scarp height, the background slope angle α
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and the initial maximum scarp slope angle θ using the Matlab code Scarp Diffusion Lab (SDL)
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[Hilley and Arrowsmith, 2003]. Subsequently, we modeled the degradation at different time steps
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using the forward modeling function in SDL. Modeling of scarp degradation is strongly
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dependent on the diffusion constant κ. We have chosen two end member diffusion constants
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(κ1 = 0.46 m²/ka, κ2 = 0.046 m²/ka) proposed as reasonable values for the hyperarid climate
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environment of the N-Chilean Atacama desert by González and Carrizo [2003]. After forward
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modeling of scarp degradation we exported the synthetic data and analyzed it using our sliding
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window approach.
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We have tested two initial maximum scarp slopes θ1 = 80° and θ2 = 60° with a background slope
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α = 0° and initial scarp heights of 1 m and 3 m. Degradation was modeled for time steps of 500 a,
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1 ka, 10 ka, 20 ka, 40 ka, 60 ka, 80 ka, and 100 ka using diffusion constants κ1 and κ2.
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Subsequently, we calculated gradient along the synthetic profiles using window sizes between 3
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and 25. The initial scarp height had no effect on the obtained results. Variation of window size
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also had no significant impact on the detection of slope breaks, but still proved useful to decrease
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noise in real data. Troughs in gradient data were recognizable over the whole range of modeled
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ages (Figures S4 – S5), but profiles with model ages over 40 ka (κ1) only introduced minor
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changes to the output as erosion acts strongest on steep surfaces. Using the lower diffusion
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constant κ2 (κ2 = κ1 * 0.1) resulted in steeper troughs for higher ages (Figures S6 – S7). This
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implies that erosion has a significant impact on our approach for detection of slope breaks. The
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initial scarp slope angle θ influences the width of the troughs in gradient data. For very low initial
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dip angles, e.g., 10°, the resulting gradient data would show broad valleys instead of steep
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troughs due to the stability of gradient over distance. However, for realistic initial values
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(θ1 = 80°, θ2 = 60°) gradient data shows prominent troughs (Figures S4 – S7).
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In a subsequent test, we used profiles with an initial maximum scarp slope of 60°, but changed
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the background slope α to 4°. All other parameters were kept the same. The gradient data shows
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prominent troughs up to 60 ka for degradation based on constant κ1 for all window sizes
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(Figure S8). Using κ2, gradient data displays prominent troughs for the entire range of tested ages
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up to 100 ka (Figure S9). Thus, for an normal fault with a realistic dip angle of ~60°, our sliding
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window approach is capable of reliably detecting slope breaks in fault scarp data over the entire
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range of time steps.
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Variation of window sizes was mainly used to improve the signal to noise ratio. Smoothing
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increased with window size. We note that the output slope angle was observed to decrease with
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increasing window size as the differentiation is carried out for an increasing amount of data
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points. The most accurate measurement of slope angle is accomplished by using the smallest
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window size. However, to derive the number of events recorded in profile data, we focused on
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detecting breaks in gradient rather than measuring absolute slope angles.
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3. Calculation of synthetic SRL
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Synthetic SRL were calculated from paleomagnitudes (Figure S10; Table 1, equation (6)), which
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were previously derived from (a) the LDI at the fault scarp and (b) displacement at knickpoints
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(KnpD) to compare them with the mapped SRL in the study areas. SRL based on LDI range from
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19.0 km to 34.2 km in the CJS, and from 12.9 km to 28.1 km in the LNS. SRL based on KnpD
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range from 8.7 km to 23.8 km for the CJS, and from 7.7 km to 19.8 km for the LNS. The
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synthetic SRL based on paleomagnitudes calculated from LDI and KnpD are in reasonable
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agreement with the mapped total length of the CJS (19 km). In case of the LNS, all synthetic SRL
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are larger than the mapped segment. Thus, for large earthquakes with Mw ~ 7, we assume an
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involvement of adjacent segments.
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4. File descriptors and supplementary figure captions
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Filename: tect20238-sup-0003-pS01.tif
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File descriptor: Aerial view of CJS
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Figure S1: Aerial view of the area depicted in Figure 2a. Aerial photographs were acquired with
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the Modular Airborne Camera System, developed by the DLR (German Aerospace Center;
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Lehmann et al., 2011; Bucher et al., 2012).
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Filename: tect20238-sup-0004-pS02.tif
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File descriptor: Aerial view of LNS
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Figure S2: Aerial view of the area depicted in Figure 3a. Aerial photographs were acquired with
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the Modular Airborne Camera System, developed by the DLR (German Aerospace Center;
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Lehmann et al., 2011; Bucher et al., 2012).
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Filename: tect20238-sup-0005-pS03.tif
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File descriptor: Profiles of selected channels
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Figure S3: Longitudinal and cross-sectional profiles of selected channels. a) Longitudinal profiles
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(A, B, C) of three selected main channels in the La Negra segment. The vertical line marks the
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intersection with the surface rupture. The profiles do not contain any knickpoints related to the
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analyzed surface rupture. b) Cross-sectional profiles of the channels in panel a). Cross-sections
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have been extracted at the surface rupture. Channel widths have been measured across the most
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deeply incised sections of the channels. c) Longitudinal profiles (D, E, F) of three gullies from
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the Cumbre Jequier segment. Knickpoints related to the analyzed surface rupture are marked with
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circles. d) Cross-sectional profiles of the gullies in panel c). Cross-sections have been extracted at
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the surface rupture. Channel widths have been measured across the most deeply incised sections
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of the channels.
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Filename: tect20238-sup-0006-pS04.tif
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File descriptor: Synthetic profiles
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Figure S4: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ1 = 80°, data point spacing d = 0.1 m, background slope angle α = 0°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ1 = 0.46 m²/ka. a) Synthetic profile data. b) Calculated gradient data, window
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size = 3. Inset shows zoom between -10 and +10 m. c) Calculated gradient data, window
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size = 25. Inset shows zoom between -10 and +10 m.
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Filename: tect20238-sup-0007-pS05.tif
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File descriptor: Synthetic profiles
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Figure S5: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ2 = 60°, data point spacing d = 0.1 m, background slope angle α = 0°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ1 = 0.46 m²/ka. a) Synthetic profile data. Inset shows zoom between -20 and
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+10 m. b) Calculated gradient data, window size = 3. Inset shows zoom between -10 and +10 m.
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c) Calculated gradient data, window size = 25. Inset shows zoom between -10 and +10 m.
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Filename: tect20238-sup-0008-pS06.tif
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File descriptor: Synthetic profiles
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Figure S6: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ1 = 80°, data point spacing d = 0.1 m, background slope angle α = 0°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ2 = 0.046 m²/ka. a) Synthetic profile data. b) Calculated gradient data,
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window size = 3. Inset shows zoom between -10 and +10 m. c) Calculated gradient data, window
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size = 25. Inset shows zoom between -10 and +10 m.
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Filename: tect20238-sup-0009-pS07.tif
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File descriptor: Synthetic profiles
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Figure S7: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ2 = 60°, data point spacing d = 0.1 m, background slope angle α = 0°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ2 = 0.046 m²/ka. a) Synthetic profile data. Inset shows zoom between -20 and
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10 m. b) Calculated gradient data, window size = 3. Inset shows zoom between -10 and +10 m.
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c) Calculated gradient data, window size = 25. Inset shows zoom between -10 and +10 m.
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Filename: tect20238-sup-0010-pS08.tif
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File descriptor: Synthetic profiles
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Figure S8: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ2 = 60°, data point spacing d = 0.1 m, background slope angle α = 4°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ1 = 0.46 m²/ka. a) Synthetic profile data. Inset shows zoom between -20 and
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5 m. b) Calculated gradient data, window size = 3. Inset shows zoom between -20 and +20 m.
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c) Calculated gradient data, window size = 25. Inset shows zoom between -20 and +20 m.
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Filename: tect20238-sup-0011-pS09.tif
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File descriptor: Synthetic profiles
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Figure S9: Synthetic profiles generated with SDL [Hilley and Arrowsmith, 2003]. Initial scarp
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slope angle θ2 = 60°, data point spacing d = 0.1 m, background slope angle α = 4°. Consecutive
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time steps from 0 a to 100 ka are marked with different colors. Diffusion constant for degradation
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forward modeling κ2 = 0.046 m²/ka. a) Synthetic profile data. Inset shows zoom between -20 and
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5 m. b) Calculated gradient data, window size = 3. Inset shows zoom between -15 and +15 m.
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c) Calculated gradient data, window size = 25. Inset shows zoom between -15 and +15 m.
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Filename: tect20238-sup-0012-pS10.tif
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File descriptor: Synthetic SRL from moment magnitude (Mw)
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Figure S10: Synthetic SRL calculated from moment magnitude (Mw) using the regression
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function (Table 1, equation (6)) by Wells and Coppersmith [1994]. Magnitudes used for
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calculation of SRL have been previously determined based on measured displacement (LDI, and
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KnpD). The hatched boxes mark the range of magnitudes and the resulting synthetic SRL.
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