We have intensity information for the 1811-1812 earthquakes. Comparing the estimated intensity contours that include the effects of local geology to the December 16, 1811 intensity observations, we see that magnitude 7.7 estimates of intensity compare well at intensity five and six.
However, the magnitude 6.8 estimates of intensity compare poorly to the observations, particularly at intensity six. Thus it seems that the 1811-1812 earthquakes were middle to upper magnitude 7 events.