Numerous earthquakes occur every year throughout the state of Arkansas, but most go unnoticed. Earthquakes that are felt can be startling and serve as good reminders that Arkansas is located near one of the most hazardous earthquake zones in the country. Earthquakes have been documented in Arkansas as early as 1699 by missionaries traveling down the Mississippi River near Helena (Phillips County). Although it is uncommon for major earthquakes to occur a great distance from active tectonic boundaries, earthquakes associated with the New Madrid Seismic Zone (NMSZ) have been some of the largest earthquakes ever to strike North America. The NMSZ is an active earthquake zone extending from Cairo, Illinois, into Marked Tree (Poinsett County).
Earthquakes are caused by movement along geologic faults, or fractures in the earth’s crust. When a fault moves, energy is released and transferred through the earth, which causes the shaking experienced during an earthquake. Arkansas has hundreds, if not thousands, of faults. Most of these faults are considered inactive; however, faults associated with the New Madrid Seismic Zone are still active. They are deeply buried beneath many layers of unconsolidated sediment and sedimentary rock, making them almost impossible to identify on the earth’s surface. These faults exist within a failed rift zone, known as the Reelfoot Rift.
On December 16, 1811, residents living in northeastern Arkansas were jolted awake at 2:15 a.m. by a major earthquake. The shaking was felt as far away as New England and Canada. Scientists estimate that this event measured 7.0 to 8.0 in magnitude. This marked the first in a series of powerful earthquakes to shake the region over a three-month period.
Other notable New Madrid Seismic Zone earthquakes in Arkansas include an estimated magnitude 6.0 earthquake reported near the town of Marked Tree on January 4, 1843. This earthquake caused the land to subside, which formed new lakes, and it damaged chimneys and brick structures. A magnitude 5.0 earthquake was recorded on March 24, 1976, in Poinsett County. This earthquake was felt over an area of 174,000 square miles. Damage included power outages and downed telephone lines in Jonesboro (Craighead County), broken windows in Paragould (Greene County), cracked plaster in Marked Tree, and roof damage and fallen ceiling tile in Decatur (Benton County). Although significant damage has not been reported in recent years, the New Madrid Seismic Zone is potentially capable of generating powerful earthquakes.
Earthquakes can occur nearly anywhere in Arkansas. Earthquakes that occur outside of the New Madrid Seismic Zone are generally small and have caused little to no damage. One of the most memorable earthquakes outside the NMSZ occurred on New Year’s Day in 1969 near Ferndale (Pulaski County) and was felt over northern and central Arkansas. Residents of Little Rock (Pulaski County) reported cracked plaster and shifted furniture. This earthquake also caused trees, utility lines, and tall buildings to sway. Many people reported having difficulty standing. The earthquake was estimated to be 4.2 to 4.5 in magnitude.
When numerous earthquakes occur in a localized area over a short period of time, it is generally referred to as an earthquake swarm. Earthquake swarms have occurred in Arkansas near Arkadelphia (Clark County), El Dorado (Union County), Enola (Faulkner County), and Magnet Cove (Hot Spring County). Of these earthquake swarms, the most noteable is the Enola Swarm in central Arkansas. On January 12, 1982, an earthquake of magnitude 1.2 was recorded near Enola. Since then, more than 40,000 earthquakes have been recorded in the Enola area. Most of the recorded seismic events are microquakes, which are small earthquakes. Earthquakes in the Enola Swarm area have not exceeded a magnitude of 4.5. No structural damage has been reported. On May 4, 2001, a magnitude 4.4 earthquake occurred in the Enola area, followed by aftershocks, some of which measured greater than a magnitude 2.0. Approximately 2,500 earthquakes were recorded in the Enola area in 2001 by a portable seismic monitoring network. Another earthquake swarm began in late 2010 in the region of Guy (Faulkner County) and Greenbrier (Faulkner County); the most powerful of these to date was a 4.7 magnitude earthquake which occurred on the night of February 27, 2011.
Recently, evidence for large historical earthquakes has been found outside the New Madrid Seismic Zone in Drew, Phillips, and Ashley counties. Research is being conducted to better understand the source of past earthquake events in these areas.
For additional information:
Chui, Jer-Ming, Arch C. Johnson, Ann G. Metzeger, Linda Haar, and Jon Fletcher. “Analysis of Analog and Digital Records of the 1982 Arkansas Earthquake Swarm.” Bulletin of the Seismological Society of America 74 (October 1984): 1721–1742.
Jackson, Kern C. Earthquakes and Earthquake History of Arkansas. Arkansas Geological Commission Information Circular 26. Little Rock: Arkansas Geological Commission, 1979.
Johnston, A., et al. The Central Arkansas Earthquake Swarm. Special Report 8. Memphis: Tennessee Earthquake Information Center, 1982.
Majenu, Minella F. “The Structural Analysis of Enola and Greenbrier, Arkansas Earthquake Swarms: Cause and Effect?” MS thesis, University of Arkansas, 2015.
McFarland, J. D. “Faulkner County Earthquakes.” Little Rock: Arkansas Geological Commission, 2001.
Arkansas Geological Survey