Auxiliary Material: Convergence test of presented dynamic rupture simulations
To show that the simulations are convergent, we carry out the convergence test for difference element sizes. There are 5 GLL nodes in each spectral element, so the average grid interval is a quarter of the element size. The test simulations have the same frictional parameters and fault zone velocity contrasts, except that the element size varies. We show in the figure "fs01.eps" the RMS of rupture time difference relative to the finest simulation with element size of 0.0625 Lc for both 2 Lc and 4 Lc wide fault zones. We find that the wider the fault zone is, the larger the RMS error is. But the 4 Lc simulations converge faster, and the RMS error for element size of 0.1 Lc is negligible for both 2 Lc and 4 Lc cases.