Strong motion data observed directly above a rupture zone of the Michoacan, Mexico, earthquake in 1985 provide, for the first time, clear evidence for crack-like rupture process in a major earthquake. The observed simple ramp-function type displacements cannot be explained by dislocation models such as a stepfunction dislocation, but require a crack-like slip function which grossly satisfies stress conditions on the fault (i.e., stress drops to some finite level after a passage of rupture front). This conclusion is required because the records contain sufficient near-field terms to distinguish between the two models. ¿ American Geophysical Union 1988