Geographic Patterns of Faults and Earthquakes
The fracturing and movement of the Earth's surface have been linked to stresses created by movements of molten rock within the asthenosphere. Convection currents within this subsurface region tug at crustal plates, driving them into or past one another, or pulling them apart. Thus, the patterns of earthquakes and faults are closely associated with the boundaries of plates. These patterns can be seen in the daily occurrence of earthquakes shown in the Google Earth overlay below.
Figure 15.30 Worldwide M1+ Earthquakes, Past 7 Days
Real-time, worldwide earthquake list for the past 7 days (Courtesy USGS)
Figure 15.31 New Madrid Seismic Zone
Courtesy USGS (Source)
Though faulting and earthquakes are common along plate boundaries, they also occur in zones of weakness within the interior of a plate. The New Madrid Seismic Zone is the site of one of the largest earthquakes to strike North America (1811-1812). Though it had relatively little effect on human populations due to its location in a sparsely populated area at the time, it had a significant impact on the natural environment. The largest earthquakes caused the Mississippi River to flow backwards and low water falls were formed from the fracturing of the earth. 150,000 acres of forest ere destroyed and Reelfoot Lake, KY was formed. Now, several large population centers could be affected by the seismic zone. The seismic zone can be seen in Figure 15.31.
Watch "Hidden Fury"
(Provided by the USGS and the Open Video Project)
This video uses 3-D map animations to locate and characterize the New Madrid Earthquake Zone in the Mississippi River Valley. It relives newspaper article accounts of a series of great earthquakes that occurred between 1811 - 1812 and includes animation of how the Mississippi River Valley was created. Computer plots of the epicenters show how the fault is mapped.