Extended Data Fig. 7: Model showing the actual and apparent rupture speeds.

a, Schematics showing a dynamic rupture originating within the gouge layer at O and reaching the surface of observation at the location A at time \({t}_{0}\), while propagating at a rupture speed V_act. As the rupture front swipes through the free surface, where measurements are performed, it results in an apparent rupture speed V_app. b, c, Maps of slip-velocity histories for ruptures E, with black lines outlining the position of the rupture front. d, e, Contour lines of the rupture fronts (black lines), the same as in b, c, and the fit using the analytical model (blue lines) described in the text. f, g, The apparent rupture speed on the free surface, for events E in sequences 1 and 2, respectively, showing unphysical initially supersonic rupture speeds. Using the model in a, these unphysical apparent rupture speeds can be explained by the actual rupture speeds of 0.16 c_s and 0.36 c_s, respectively.