Numerous earthquakes occur every year throughout the State of Arkansas, but most go unnoticed.
The other scale often used to indicate earthquake size is the Modified Mercalli Intensity scale. In general earthquakes smaller than magnitude 2.5 will not be felt in most situations, they are simply too small and will certainly do no damage. The amount of time that passes between the arrival of the Primary wave and the Secondary wave allows seismologists to determine the distance from the seismic station to the earthquake epicenter. The quakes are shown on the Center for Earthquake Research and Information central North American earthquake map.
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. When a fault moves, energy is released and transfers through the earth causing the shaking that is experienced during an earthquake.
When a seismic station records a P wave arrival, the longer it takes for the S wave to arrive, the farther away the earthquake epicenter.

Most Kansans have never felt a tremor, but more than 100 earthquakes rumbled through the state betwen 1977 and 1989. Earthquakes have been historically documented in Arkansas, as far back as 1699, by missionaries traveling down the Mississippi River near Helena (Phillips County), Arkansas.
About 5% of earthquakes are intraplate earthquakes and occur in the center of a tectonic plate. It is a subjective scale relying on the observations of people trained to relate the earthquake effects to a numeric scale from I-X+ (Roman numerals are used to distinguish this as an empirical scale). This circular acquaints the reader with the theory of plate tectonics, recording and measuring methods, and earthquake activity in Kansas. Although, it is uncommon for major earthquakes to occur far away from active tectonic boundaries, earthquakes associated with the New Madrid seismic zone (NMSZ), an active earthquake zone extending from Cairo, Illinois, into Marked Tree (Poinsett County), Arkansas, have been some of the largest earthquakes to ever strike North America. Most people (but not all) in an area experiencing Intensity III effects will just feel the earthquake shock. Therefore, if a magnitude 3 earthquake shows a record trace displacement of 1mm, then a magnitude 4 earthquake will show a trace displacement of 10mm.

An earthquake of magnitude 7 will cause near total devastation in the epicentral area and cause structural damage and collapse of poorly-built structures over a much larger area (remember, this earthquake is 30 times more powerful than a magnitude 6 event).
A magnitude 2 earthquake is then equal to 1,800 kilograms of explosive energy (approximately 56 times 33). The great earthquakes, those over magnitude 8, will destroy most of the infrastructure in a very large area, several 10s of miles in diameter, and can cause structural damage and collapse of poorly-built structures as much as 100 miles away. A magnitude 7 earthquake releases 56,000,000,000 kilograms of explosive energy compared to a magnitude 8 earthquake which releases 33 times more energy.

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