How fast plates are moving

Volcanic activity and earthquakes occur at divergent boundaries, but they are not as violent as those at convergent boundaries. Where plates diverge below the ocean, magma molten rock rises from the mantle to fill the space between the plates and solidifies, forming underwater mountain ranges called mid-ocean ridges. On land, rift valleys form where plates diverge. A good example of this is the East African rift valley.

At transform boundaries, plates are sliding past each other horizontally in different directions. Transform boundaries can produce great earthquakes, but volcanoes are rare.

The San Andreas fault, which separates the North American plate from the Pacific plate and is responsible for many of California's earthquakes, is located on a transform boundary. As the plates move, their rough edges can get stuck on each other. This stops movement at the boundary while the rest of the plates keep moving. Stress builds up, and when it becomes too much, the plates suddenly slip past one another, and the rocky, brittle lithosphere cracks. These cracks are called faults.

It is the energy released by the sudden movement on these faults that causes most earthquakes. Plate boundaries are made up of many faults. How plates move relative to each other determines, in part, the type of faults at their boundaries. There are three basic types of faults: reverse or thrust , normal, and strike-slip.

Earthquakes are often described based on the type of fault they occur on. However, earthquakes are not typically so simple. It is common for fault movements to include both up-and-down and side-by-side movement together.

In addition, not all earthquakes occur at plate boundaries. Faults located far from plate boundaries also generate earthquakes, but less frequently, and they are difficult to explain. Seismic stations contain instruments that detect, measure, record, and transmit information about the shaking caused by an earthquake the seismic waves. Scientists rely on networks of seismic stations to determine the location and size of an earthquake.

Magnitude is the most common way to describe earthquake size. Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates.

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Meet the people trying to help. Animals Whales eat three times more than previously thought. Environment Planet Possible India bets its energy future on solar—in ways both small and big. That heat is ebbing away as Earth ages, and this was expected to slow plate motion. A study last year by Martin Van Kranendonk at the University of New South Wales in Sydney, Australia, and colleagues measured elements concentrated by tectonic action in rocks from around the world, and concluded that plate motion has been slowing for 1.

Now Kent Condie , a geochemist at the New Mexico Institute of Mining and Technology in Socorro and his colleagues have used a different approach and concluded that tectonic activity is increasing.

They looked at how often new mountain belts form when tectonic plates collide with one another. They then combined these measurements with magnetic data from volcanic rocks to work out at which latitude the rocks formed and how quickly the continents had moved. Most earthquakes are caused by large-scale movements of the Earth's lithospheric plates. Experts recognize seven to twelve major plates and a number of smaller ones. The plates take their names from continents the North American plate : from oceans the Pacific plate : and from geographic areas the Arabian plate.

The plates are in very slow but constant motion, so that seen from above, the Earth's surface might look like a slowly moving spherical jigsaw puzzle. The plates move at rates of 2 to 15 cm or several inches in a year, about as fast as our fingernails grow. On a human scale, this is a rate of movement that only the most sophisticated instruments can detect.