- Copyright © 1970, by the Seismological Society of America
The November 9, 1968 earthquake in south-central Illinois occurred in the New Madrid zone, a seismic zone associated with northeast-trending geological structure. Landforms in the epicentral area consist of nearly flat, glacial lake plains surrounding low, loess-covered hills. An extensive post office canvass and a field inspection of the epicentral area indicate that the strongest shaking (MM VII) took place in the Wabash and Ohio Valleys and adjacent lowlands of south-central Illinois. Characteristic damage included broken chimneys, fallen plaster, and occasional instances of collapsed parapets and overthrown tombstones. Observed rotations of tombstones and other objects in the epicentral area suggest a quadrant distribution of clockwise and counter-clockwise rotations.