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Nisqually Earthquake Damage on SR 302 -
South of Belfair, Washington (Photo by WSDOT)
Understanding Rupture Mechanics
Plate motion and rupture mechanics can be demonstrated diagramatically. Adjacent crustal plates or pieces of plates with little or no stress build-up may characterize an inactive fault, one with continuous creep or one in which energy has only recently been released in an earthquake.

Over time, ranging from decades to millennia, stress builds along the fault until it reaches a breaking point. Sudden slippage occurs as the stress is released, creating the ground motion of an earthquake.

Can the science of plate tectonics and rupture mechanics help in earthquake prediction? We have seen that earthquakes occur at the following three kinds of plate boundaries: ocean ridges where the plates are pulled apart, margins where the plates scrape past one another, and margins where one plate is thrust under the other. Thus, we can predict the general regions on the Earth's surface where we can expect large earthquakes in the future. We know that each year about 140 earthquakes of magnitude 6 or greater will occur within this area which is 10 percent of the Earth's surface.

But on a worldwide basis we cannot say with much accuracy when these events will occur. The reason is that the processes in plate tectonics have been going on for millions of years. Only by monitoring the stress and strain in small areas can we hope to predict when renewed activity in that part of the plate tectonics arena is likely to take place.

Move on to the "Types of Faults" page