Question: What was the initial magnitude of the earthquake that formed Lake Isom?

full_context: Document 1: List of earthquakes in 1931: This is a list of earthquakes in 1931. Only magnitude 6.0 or greater earthquakes appear on the list. Lower magnitude events are included if they have caused deaths, injury or damage. Events which occurred in remote areas will be excluded from the list as they wouldn't have generated significant media interest. All dates are listed according to UTC time. In a stark contrast to 1930, many large and destructive earthquakes occurred during 1931. The largest and deadliest event was the magnitude 7.9 earthquake which caused major devastation to China in August. New Zealand saw its worst natural disaster in February. Iran and Nicaragua had many deaths from earthquakes in the first half of the year. Other interesting events happened in Texas and the United Kingdom with the largest quakes for these areas hitting this year.
Document 2: 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. 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.
Document 3: Kenlake State Resort Park: Kenlake State Resort Park is a park located on the western shore of Kentucky Lake. The park's main entrance and most of its facilities are located in Marshall County; the park also extends into Calloway County. The mailing address of the park is Hardin, Kentucky; however, it is located much closer to the unincorporated community of Aurora, Kentucky. The nearest town of substantial size is Murray. The park encompasses 1795 acre of land, 160300 acre of water, and features climate-controlled indoor tennis courts. It was Kentucky's first state resort park. Along with Lake Barkley State Resort Park and Kentucky Dam Village State Resort Park, Kenlake State Resort Park is part of the Land Between the Lakes National Recreation Area, originally organized by the Great Depression–era Tennessee Valley Authority (TVA).
Document 4: 2011 Oklahoma earthquake: The 2011 Oklahoma earthquake was a 5.7 magnitude intraplate earthquake which occurred near Prague, Oklahoma on November 5 at 10:53 p.m. CDT (03:53 UTC November 6) in the U.S. state of Oklahoma. The epicenter of the earthquake was in the vicinity of several active wastewater injection wells. According to the United States Geological Survey (USGS), it was the most powerful earthquake ever recorded in Oklahoma; this record was surpassed by the 2016 Oklahoma earthquake. The previous record was a 5.5 magnitude earthquake that struck near the town of El Reno in 1952. The quake's epicenter was approximately 44 mi east-northeast of Oklahoma City, near the town of Sparks and was felt in the neighboring states of Texas, Arkansas, Kansas and Missouri and even as far away as Tennessee and Wisconsin. The quake followed several minor quakes earlier in the day, including a 4.7 magnitude foreshock. The quake had a maximum perceived intensity of VIII ("Severe") on the Mercalli intensity scale in the area closest to the epicenter. Numerous aftershocks were detected after the main quake, with a few registering at 4.0 magnitude.
Document 5: Lake Isom: 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.
Document 6: Lake Red Rock (Des Moines River): Originally the city of Red Rock, Lake Red Rock, also referred to as Red Rock Reservoir is a reservoir formed by Red Rock Dam on the Des Moines River, about 55 miles southeast of the city of Des Moines, Iowa, United States. The dam was completed in 1969 as a flood control project by the United States Army Corps of Engineers, creating the largest lake in Iowa. The lake is essentially confined to Marion County. The damface is a few miles west and south of Pella, and similarly, a few miles northeast of Knoxville.
Document 7: Reelfoot Lake: Reelfoot Lake is a shallow natural lake located in the northwest portion of U.S. state of Tennessee, in Lake and Obion counties. Much of it is really more of a swamp, with bayou-like ditches (some natural, some man-made) connecting more open bodies of water called basins, the largest of which is called Blue Basin. Reelfoot Lake is noted for its bald cypress trees and its nesting pairs of bald eagles. It is the site of Reelfoot Lake State Park. Lake Isom, a similar, smaller lake to the immediate south, is a National Wildlife Refuge area.
Document 8: New Madrid Seismic Zone: The New Madrid Seismic Zone (pronounced ), sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes (earthquakes within a tectonic plate) in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.
Document 9: Norris Dam State Park: Norris Dam State Park is a state park in Anderson County and Campbell County, Tennessee, in the southeastern United States. The park is situated along the shores of Norris Lake, an impoundment of the Clinch River created by the completion of Norris Dam in 1936. The park consists of 4038 acre managed by the Tennessee Department of Environment and Conservation. The park also administers the Lenoir Museum Complex, which interprets the area's aboriginal, pioneer, and early 20th-century history.
Document 10: 1909 Wabash River earthquake: The 1909 Wabash River earthquake occurred at 04:45 local time on September 27 with a maximum Mercalli intensity of VII ("Very strong"). It measured 5.1 on a seismic scale that is based on an isoseismal map or the event's felt area. With moderate damage in the Wabash River Valley, it is currently the strongest earthquake recorded in the U.S. state of Indiana. The earthquake occurred somewhere along a fault within the Wabash Valley Seismic Zone.
Document 11: Fontana Lake: Fontana Lake is a reservoir impounded by Fontana Dam on the Little Tennessee River located in Graham and Swain counties in North Carolina. The lake forms part of the southern border of Great Smoky Mountains National Park and the northern border of part of the Nantahala National Forest. Depending on water levels, the lake is about 17 mi long. The eastern end is the Tuckasegee River near Bryson City. It has an average depth of 135 ft and reaches a maximum depth of 440 ft , making it the deepest lake in North Carolina. The lake has many inlets into coves and many islands formed from former mountain peaks, especially near the eastern end. As with most dam-impounded lakes, the steep banks are exposed when water levels are low. Many towns were submerged shortly after the creation of Fontana Lake, such as Proctor and Judson.
Document 12: 2010 Indiana earthquake: The 2010 Indiana earthquake registered 3.8 on the moment magnitude scale and struck near Greentown and Kokomo on December 30, 2010 at 12:55:21 UTC at a depth of 3 mi. The quake occurred approximately 50 miles north of Indiana's capital, Indianapolis. It joins only three other earthquakes that have affected the northern Indiana area since 1999. The “extremely rare and unprecedented” earthquake had the largest magnitude of a northern Indiana earthquake in 175 years. Despite being considered a rare occurrence, the affected region of northern Indiana lies near many fault lines including the Wabash Valley Seismic Zone and the New Madrid Seismic Zone. Both zones are hotspots for tectonic activity, with the Wabash Valley Fault Zone reaching earthquake depths up to 18 km (11.4 mi.) deep. It was incorrectly recorded by nearby stations as a 4.2 magnitude before being downgraded to 3.8. No significant damage was reported from the incident, but the quake was felt by thousands, spanning across multiple cities and states. Towns as far away as Kalamazoo, Michigan and states as far as Wisconsin and Kentucky reported the earthquake.
Document 13: Lake Wayne: Lake Wayne formed in the Lake Erie and Lake St. Clair basins around 12,500 years before present (YBP) when Lake Arkona dropped in eleveation. About 20 ft below the Lake Warren beaches it was early described as a lower Lake Warren level. Based on work in Wayne County, near the village of Wayne evidence was found that Lake Wayne succeeded Lake Whittlesey and preceded Lake Warren. From the Saginaw Basin the lake did not discharge water through Grand River but eastward along the edge of the ice sheet to Syracuse, New York, thence into the Mohawk valley. This shift in outlets warranted a separate from Lake Warren. The Wayne beach lies but a short distance inside the limits of the Warren beach. Its character is not greatly different when taken throughout its length in Michigan, Ohio, Pennsylvania and New York. At the type locality in Wayne County, Michigan, it is a sandy ridge, but farther north, and to the east through Ohio it is gravel. The results of the isostatic rebound area similar to the Lake Warren beaches.
Document 14: 2003 Alabama earthquake: The 2003 Alabama earthquake took place on April 29 at 3:59 A.M. Central Daylight Time (local time when the event occurred) eight miles (13 km) east-northeast of Fort Payne, Alabama. The number of people who felt this quake was exceptionally high as the earthquake could be felt in 11 states across the East Coast and as far north as southern Indiana. The earthquake was strongly felt throughout metropolitan Atlanta. The Georgia Building Authority was called out to inspect the historic Georgia State Capitol in downtown Atlanta and other state-owned buildings, but found no problems. However, this is not out of the ordinary as earthquakes east of the Rocky Mountains can be felt several times the area felt on West Coast earthquakes. The earthquake was given a magnitude 4.6 on the moment magnitude scale by the USGS (other sources reported as high a magnitude as 4.9) and reports of the duration of the shaking range from 10 seconds to as long as 45 seconds. It is tied with a 1973 earthquake near Knoxville, Tennessee as the strongest earthquake ever to occur in the Eastern Tennessee Seismic Zone, which is the second most active seismic zone east of the Rocky Mountains, with the New Madrid Seismic Zone the most active.
Document 15: Clear Lake (Iowa): Clear Lake is the name of a natural spring fed body of water located in Cerro Gordo County, Iowa near Clear Lake, Iowa. It is approximately 3684 acre in size. It is a popular fishing destination, with walleye, bullhead, yellow bass and channel catfish. People from Des Moines and Minneapolis–Saint Paul have had homes on the shores of the lake since the 1870s. The average depth is 10 ft and the maximum depth is 30 ft , in the dredged area of the west end. The lake has 13.6 mi of shoreline. As of 2004, the lake has seen major efforts undergone to restore its natural clarity, including filtration systems, dredging, and education of local farmers to reduce toxic pesticides from entering the lake. Clear Lake has been named the "Best Iowa Lake Town" by "The Des Moines Register" and "A Top Vacation Spot" by "Midwest Living" magazine.
ground_truth: 7.5–7.9