Rupture propagation along the fault strike obtained from the projection to the linear fault. The horizontal axis is time, the same axis as Fig. 3. The vertical axis is the distance along the linear fault. Positive and negative distances correspond to the northeast and the southwest from the reference near the epicenter, respectively. A slope on the plot is proportional to the rupture velocity. For reference, 2 km/s and 4 km/s are shown by thick lines.