Actually, there's not a simple relationship between magnitude and intensity. Surface wave amplitude depends on a lot more than the size of the earthquake. (e.g. rupture depth, surficial geology, etc)
Moment magnitude is broadly calibrated to be similar to the old Richter scale, which was based (more or less) on log10 of the surface wave amplitude. However, the surface wave relationship only holds for mid-size earthquakes in southern California. It's different for larger earthquakes and different regions.
Either way, it is fair to say that the peak ground acceleration was not 30 times greater, and was significantly less (probably close to 10x, but could be a lot less or slightly more). It's not a simple relationship, at any rate.
