al., 1984). More useful are the estimates of the likely amount of ground shaking that can be expected, contained in the National Seismic Hazard maps. Most large earthquakes around the world have induced liquefaction.Over the past decade, paleoseismic studies have begun to unravel the earthquake history of the New Madrid seismic zone. In this way, sand blows across the New Madrid region were found to have formed during earthquakes about 1450 A.D., 900 A.D., 300 A.D., and 2350 B.C.Photograph of sand blow deposit and related feeder dike exposed in excavation. Furthermore, sand blows attributed to the 1450 A.D., 900 A.D., and 2350 B.C. These observations support the interpretation that the prehistoric events were similar in location and magnitude to the 1811-1812 earthquakes and also suggests that they too were earthquake sequences. The New Madrid seismic zone is located in the northern part of what has been called the Mississippi embayment. Earthquake-induced liquefaction features are distinctive and form as the result of strong ground shaking.Liquefaction features include sand blows, dikes, and sills. Sand dike fills fissure that formed in soil. In eastern North America, where near-surface faulting is uncommon or difficult to identify, paleoseismology often employs liquefaction features to learn about prehistoric earthquakes. The Mississippi embayment is a broad trough filled with marine sedimentary rocks about 50-100 millions years old and river sediments less than 5 millions years old. 20 cool facts about the New Madrid Seismic Zone-Commemorating the bicentennial of the New Madrid earthquake sequence, December 1811-February 1812 [poster]; 2011; GIP; 134; Williams, R. A.; McCallister, N.S. If we use the data on historical seismicity combined with the new information on recurrence of large earthquakes, and make the same assumptions that go into the National Seismic Hazard maps, we would estimate a 25-40% chance of a magnitude 6.0 and greater earthquake in the next 50 years and about a 7-10% probability of a repeat of the 1811-1812 earthquakes in the same time period.However, it is VERY important to note that these estimates alone do not include information about WHERE the earthquakes might occur and therefore what shaking might affect any given location. Sand blows formed over an extremely large area about 10,400 square kilometers. Three earthquakes in this sequence had a magnitude (M) of 7.0 or greater. Our house cracked and quivered, so we were fearful it would fall to the ground. Effects of liquefaction extended about 200 km northeast of the New Madrid seismic zone in White County, Illinois, 240 km to the north-northwest near St. Louis, Missouri, and 250 km to the south near the mouth of the Arkansas River. Radiocarbon dating of plant remains is the most commonly used dating technique in paleoseismology. It is preferable to have radiocarbon dates from both overlying and underlying horizons to bracket the age of the sand blow.Log of trench wall at Dodd site near Steele, Missouri, where sand blow and two associated sand dikes are exposed. Other relatively young faults, which are not necessarily associated with recent earthquakes, or the main seismicity trend in the New Madrid region, are shown in this map. )Photograph of some diagnostic artifact types in New Madrid region: 1, Campbell Appliqué; 2, Bell Plain; 3, Nodena Elliptical point; 4, Nodena Banks variety point; 5, Parkin Punctate; 6, Madison point; 7, Varney Red Filmed; 8, Barnes Cord Marked; 9, daub with wattle impression. Not one in the family knew at the time that it was an earthquake. Studies focusing on earthquake-induced liquefaction features utilized archaeology and radiocarbon dating to estimate the ages of liquefaction features, and thus, the timing of the earthquakes that caused them. "After the earthquake [of 1811-1812] moderated in violence, the country exhibited a melancholy aspect of chasms, of sand covering the earth, of trees thrown down, or lying at an angle of forty-five degrees, or split in the middle. (Photo by Martitia Tuttle, NEHRP-funded research. However, there are ideas that are being researched.