See animation of "normal" fault at USGS
True or False?
Earthquakes the magnitude 6.3, like that which devastated Christchurch, New Zealand on February 21, 2011, are rare.
According to Dr. Roger Musson, a seismologist at the British Geological Survey, occurrence of earthquakes of magnitude 6.3 are quite common--about every three days! However, most earthquake epicenters are in locations where little damage or loss of human life can occur. The most recent earthquake in Japan was in another league entirely, of a magnitude of 8.9 on the Richter scale. The March 11, 2011 Honshu earthquake is the sixth largest recorded since the year 1900.
Most earthquakes result from a sudden release of seismic energy caused when two parts of the earth's crust, or tectonic plates, slip over or past one another. The greatest risk of earthquake exists along fault lines between major tectonic plates, such as California's San Andreas fault. However, even we midwesterners can look forward to some seismic activity, thanks to rifts in the earth's crust beneath the Mississippi River valley. The largest rift, the Reelfoot, is located in Missouri's New Madrid Seismic zone, about 450 miles southwest of Chicago. In 1811 and 1812, the New Madrid zone produced some of the biggest earthquakes in U.S. history. Estimated to have a magnitude between 7.5 and 7.7, the earthquakes reportedly caused the Mississippi river to reverse course, and tremors were felt as far away as Canada.
New Madrid Seismic Zone. USGS
For more information on earthquakes past and present, the U.S. Geological Survey Earthquakes site provides extensive documentation, mapping and useful animations explaining concepts. The National Oceanic and Atmospheric Administration has up-to-date information on tsunamis, including some incredible animations of past and projected paths of earthquake-induced tsunamis. For further reading on the New Madrid earthquakes, University of Memphis' Center for Earthquake Research and Information provides some fascinating first-person accounts.