Question: What was the initial magnitude of the earthquake that formed Lake Isom?
Sentence (from "1811–12 New Madrid earthquakes"): 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.
Relevant evidence: Yes