Table S1. Explanation of diffusion modelling parameters and symbols.
Symbol	Explanation	Units	
a	Half vertical surface offset   	m	
β1	Average lower fan slope        	-	
β2	Average upper fan slope        	-	
t	time     	ka	
u	relative elevation             	m	
x	fault perpendicular distance   	m	
α	tangent of the angle of repose	-	
κ	mass diffusivity               	m2	
Figure S1:  Calculated diffusion ages (κt) for 46 scarp profiles shown in Supplemental Figures 4-10, using the finite-slope solution assuming linear-diffusion and an assumed initial slope of 35°. The mean κt value of 27 m2 is denoted by the horizontal red line, with the 1 sigma (68%) standard deviation shown by the light grey band (+/- 18m2). The dark grey band represents the standard error of the mean for this sample population (+/- 2.8 m2). The 68% confidence on the mean κt value is denoted by the dark grey bar (21-27 m2), the standard error in the mean being 2.6 m2. Histograms of vertical surface offsets and κt values are shown by the blue bars around the edge.

Figure S2:  Idealised geometry of a strike-perpendicular elevation profile of a fault scarp with a vertical surface offset 2a at distance x=0 in an alluvial fan surface with a pre-existing far-field average lower slope β1 and upper slope β2, and an assumed initial angle of repose for the fault scarp of α.

Figure S3. Locations of DGPS profile sites S1 to S9  along the Egiin Davaa rupture. All the profiles from each site are presented, in order, in Supplemental Figures 4 to 12. Sites 8 and 9 with four profiles each are on a separate rupture and are not included in the analysis presented in Figure S1.

Figure S4. Fault scarp DGPS profiles for site 1 (99.42°E, 46.95°N) are shown by the thin grey lines (red in pdf version). The two linear fits to the fan slope below (1) and above (2) the scarp are shown by dashed black lines and the slope angles are numbered in the corners. The fault vertical offset is denoted by the black line and number. The modelled diffusion profile is indicated by the thick grey line (blue in pdf version) and the value for the diffusion age (m2) is also given. There is no vertical exaggeration in the display of profiles. The maximum scarp slope at site 1, averaged from all profiles, is 16 +/- 5°. The location of the site is shown in Figure S1.

Figure S5. Fault scarp DGPS profiles for site 2 (99.45°E, 46.96°N). The maximum scarp slope at site 2, averaged from all profiles, is 18 +/- 6°. Rest of caption as for Figure S4.

Figure S6. Fault scarp DGPS profiles for site 3 (99.46°E, 46.98°N). The maximum scarp slope at site 3, averaged from all profiles, is 11 +/- 1°. Rest of caption as for Figure S4.

Figure S7. Fault scarp DGPS profiles for site 4 (99.52°E, 47.00°N). The maximum scarp slope at site 4, averaged from all profiles, is 21 +/- 7°. Rest of caption as for Figure S4.

Figure S8. Fault scarp DGPS profiles for site 5 (99.65°E, 47.03°N). The maximum scarp slope at site 5, averaged from all profiles, is 15 +/- 1°. Rest of caption as for Figure S4.

Figure S9. Fault scarp DGPS profiles for site 6 (99.74°E, 47.12°N). The maximum scarp slope at site 6, averaged from all profiles, is 26 +/- 6°. Rest of caption as for Figure S4.

Figure S10. Fault scarp DGPS profiles for site 7 (99.76°E, 47.12°N). The maximum scarp slope at site 7, averaged from all profiles, is 29 +/- 5°. Rest of caption as for Figure S4.

Figure S11. Fault scarp DGPS profiles for site 8 (99.69°E, 46.82°N). Site 8 with four profiles is on a separate rupture and is not included in the analysis presented in Supplementary Figure 1. Rest of caption as for Figure S4.

Figure S12. Fault scarp DGPS profiles for site 9 (99.71°E, 46.83°N). Site 9 with four profiles is on a separate rupture and is not included in the analysis presented in Supplementary Figure 1. Rest of caption as for Figure S2.