STEREOGRAM OF CONVULSION SERIES

High banks caved and collapsed into the river sand bars and points of islands gave way whole islands disappeared. Huge waves on the Mississippi River overwhelmed many boats and washed others high onto the shore. Deep seated landslides occurred along the steeper bluffs and hillslides large areas of land were uplifted permanently and still larger areas sank and were covered with water that erupted through fissures or craterlets. The earthquakes caused the ground to rise and fall - bending the trees until their branches intertwined and opening deep cracks in the ground. Shaking Caused Sand Blows, River Bank Failures, Landslides, and Sunken Land However, shaking strong enough to alarm the general population (intensity greater than or equal to V) occurred over an area of 2.5 million square kilometers. The extent of the area that experienced damaging earth motion, which produced Modified Mercalli Intensity greater than or equal to VII, is estimated to be 600,000 square kilometers. The first earthquake of Decemcaused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. Nuttli also noted that about eighteen hundred earthquakes of about M3.0 to 4.0 during the same period. In total, Otto Nuttli reported more than 200 moderate to large aftershocks in the New Madrid region between December 16, 1811, and March 15, 1812: ten of these were greater than about 6.0 about one hundred were between M5.0 and 5.9 and eighty-nine were in the magnitude 4 range. This would make a total of seven earthquakes of magnitude M6.0-7.5 occurring in the period Decemthrough February 7, 1812. These three events are believed to range between M6.0 and 6.5 in size and to be located in Arkansas and Missouri. At least three other large aftershocks are inferred from historical accounts on December 16 and 17. The first and largest aftershock occurred on Decemat about 7:15 am. The earthquake ground shaking was not limited to these principal main shocks, as there is evidence for a fairly robust aftershock sequence. The second principal shock, M7.3, occurred in Missouri on January 23, 1812, and the third, M7.5, on February 7, 1812, along the Reelfoot fault in Missouri and Tennessee. The first principal earthquake, M7.5, occurred at about 2:15 am (local time) in northeast Arkansas on December 16, 1811. A Robust Aftershock Sequence for each Main Shock The magnitudes of the three principal earthquakes of 1811-1812 described below are the preferred values taken from research involved with producing the 2014 USGS National Seismic Hazard Map.

STEREOGRAM OF CONVULSION SERIES

Because there were no seismographs in North America at that time, and very few people in the New Madrid region, the estimated magnitudes of this series of earthquakes vary considerably and depend on modern researchers' interpretations of journals, newspaper reports, and other accounts of the ground shaking and damage. The area of strong shaking associated with these shocks is two to three times as large as that of the 1964 Alaska earthquake and 10 times as large as that of the 1906 San Francisco earthquake. They were by far the largest east of the Rocky Mountains in the U.S. On the basis of the large area of damage (600,000 square kilometers), the widespread area of perceptibility (5,000,000 square kilometers), and the complex physiographic changes that occurred, the New Madrid earthquakes of 1811-1812 rank as some of the largest in the United States since its settlement by Europeans. Louis, Missouri and Natchez, Mississippi. This sequence of three very large earthquakes is usually referred to as the New Madrid earthquakes, after the Missouri town that was the largest settlement on the Mississippi River between St. A Sequence of Three Main Shocks in 1811-1812

Stereogram of convulsion