Question: What was the initial magnitude of the earthquake that formed Lake Isom?
Related documents: [0]  [DOC] The 1811–12 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude 7.5–7.9 on December 16, 1811, followed by a moment magnitude 7.4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within the US state of Missouri. [END] 
[1]  [DOC] Lake Isom is a small natural lake located in Lake County, Tennessee immediately south of Reelfoot Lake. It is fed by Running Reelfoot Bayou, the outlet stream of Reelfoot Lake. Like Reelfoot, it was formed in the 1811–12 New Madrid earthquakes and it is very shallow and swampy. The entire lake and its environs, covering 1,846 acres (747 ha) comprise the Lake Isom National Wildlife Refuge and have been such since 1938. [END] 
Answer: 
7.5–7.9
7.5–7.9