A 20 x 12 grid of spring-slider cells is loaded at rate vL. A cell slips when stress exceeds mu_s and drops to mu_k; part of the released stress is passed to its four neighbours, so ruptures can cascade.
stress += k vL dt
slip when stress > mu_s -> stress = mu_k
M0 = mu A D (mu = 3e10 Pa, D = 0.1 x total slip)
Mw = (log10 M0 - 9.1) / 1.5
Gutenberg-Richter: log10 N = a - b Mw