Poster of the New Madrid Earthquake Scenario of 16 May 2011 - Magnitude 7.7

Tectonic Summary

The New Madrid seismic zone of southeast Missouri and adjacent States is the most seismically active in North America east of the Rockies. During the winter of 1811-1812, three very large earthquakes devastated the area and were felt throughout most of the Nation. Hundreds of aftershocks, some severely damaging by themselves, continued for years. Prehistoric earthquakes similar in size to those of 1811-1812 occurred in the middle 1400's and around 900 A.D. Strongly damaging earthquakes struck the southwestern end of the seismic zone near Marked Tree, Arkansas in 1843 (magnitude 6.0), and the northeastern end near Charleston, Missouri in 1895 (magnitude 6.6). Since 1900, moderately damaging earthquakes have struck the seismic zone every few decades. Earthquakes in the central and eastern U.S. are typically felt over a much broader region than in the western U.S. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage out to 40 km (25 mi).

Earthquakes everywhere occur on faults within bedrock, usually several miles deep. The earthquakes of the New Madrid seismic zone occur within a large network of faults called the Reelfoot rift. The rift formed about 500 million years ago, when this region was stretched in the northwest-southeast direction. Along a northeast-southwest zone at least 70 km (40 mi) wide and 500 km (300 mi) long, the rocks in the rift were slowly dropped down about 1-2 km (1 mi) along some of the faults. Now the region is undergoing east- west shortening, and the ancient faults of the Reelfoot rift are being reactivated to generate earthquakes. Today the Reelfoot rift and the New Madrid seismic zone are 2,000 km (1,200 mi) from the nearest plate boundary, which is in the Caribbean Sea.

The network of faults in the seismic zone is buried beneath hundreds to thousands of feet of sand and mud and rock. Four of the largest faults are recognized as alignments of abundant small earthquakes, and movements along two of these faults dammed rivers and created lakes during the earthquakes of 1811-1812. A few more deeply buried faults were detected during oil and gas exploration, and a few small faults are known from geologic mapping. However, many earthquakes occur away from the few known faults, so there must be additional, unknown faults that can generate earthquakes in the seismic zone. Accordingly, the best overall guide to seismic hazard in the New Madrid seismic zone is the earthquakes themselves.

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Earthquake Scenario

This scenario is for planning purposes only. It is not intended to be representative of what may or may not happen in a real earthquake, which is impossible to predict.

At 09:00AM on Monday May 16, 2011, magnitude 7.7 earthquake strikes along the New Madrid Seismic Zone (NMSZ) in Northeastern Arkansas. The most damaging shaking occurs in Northeastern Arkansas, Western Tennessee, the Bootheel of Missouri, Western Kentucky, and Southern Illinois. Less severe but still damaging shaking occurs in an area stretching from St. Louis, Missouri southward to Grenada, Mississippi and from Little Rock, Arkansas east to Nashville, Tennessee. This is the largest earthquake to hit the region since 1811. Ground shaking from the main shock lasts for approximately 1-2 minutes in some areas. Aftershocks of varying intensity are felt throughout the region for several days after the main shock, and cause further damage to structures already weakened by previous shaking. Tremors are felt as far away as the east coast of the United States, and damage is seen in at least eight states.

As a result, there are an estimated 100 fatalities and more than 2,500 people with injuries requiring hospitalization. Thousands are missing and thousands of earthquake victims homes and possessions are destroyed or damaged. Partial levee collapses and high water conditions due to heavy spring rains result in flooding along the Mississippi River. Most of the region is experiencing shortages of essential supplies. Damaged bridges and roadways and damage to shipping vessels cause oil and hazardous material (HAZMAT) contamination in cities, towns, waterways, and farmland in the affected area. Across the affected states widespread damage occurs to drinking water distribution and wastewater collection systems as well as treatment facilities, the national power grid, oil and natural gas pipelines, and roadways. Large structural fires break out because of damage to gas pipelines.

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