We really have no historical record of the New Madrid fault beyond the last 200 years. Both faults are a system of faults from a failed rift that could have split North America up the Mississippi Valley, similar to what is happening in Africa from the triple point near Djibouti and south through the Rift Valleys that created Lake Tanganyika, Lake Malawi, etc. (and will eventually create another island/subcontinent or two like India and Madagascar). Since the New Madrid and Wabash faults aren't very active comparatively and buried under miles of Mississippi Delta sediment, they are very hard to study.