The theory of plate tectonics

How and why tectonic plates move

The Theory of Plate Tectonics explains how and why crustal plates move around the Earth. It also explains why the Pacific Ocean has so many volcanoes, large earthquakes and tsunamis. It gives us a basic understanding of how our planet is changing. It explains how mountains form, why crustal plates move and where great earthquakes are likely to occur.

Icy crevasse on Iceland, Photo by Sarah Masters

Visitor to Iceland walks on an icy crevasse, Sarah Masters

Plate Tectonic boundaries

Seismologists discovered earthquake zones around large blocks of the Earth's crust. Researchers found a divergent boundary formed when crustal plates separated.  Divergent boundaries form the global mid-ocean ridge system which is the  longest mountain chain on Earth.

Subduction zones

Subduction zones are areas on the surface of the Earth where two tectonic plates come together.  Scientists discovered a convergent boundary formed between  the  crustal plates as they converged forming a subduction zone. Scientists also discovered ocean trenches separated the two plates on the ocean floor at convergent boundaries in subduction zones.

Our Earthquakes textbook contains sixteen chapter. Each chapter includes a lesson, quiz and activities about how and where earthquakes occur.  Chapters include information about earthquake faults, seismic waves, Mercalli scale, and tsunamis.             Myrna

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the Pacific Plate and Nazca Plate

The Pacific Plate contains the largest ocean on Earth. Crustal plates are converging on the Pacific Plate creating subduction zones where great earthquakes occur. The Nazca Plate and Pacific Plate are converging. 

The largest earthquake in the 20th occurred with the two plate converged off the coast of Chile. The earthquake's epicenter of the magnitude 9.5 earthquake occurred in the subduction zone where the two plates broke along the fault line.

Mid-Atlantic Ocean Ridge

The Mid-Atlantic Ridge is a mid-ocean ridge that runs down the middle of the Atlantic Ocean. Plate movements along the ridge produce small earthquakes that produce P waves and S waves as basalt lava pours out of fissures on the ocean floor.  Iceland sits on the Mid-Atlantic Ridge over a hot spot. The picture above shows a rift valley that formed above sea level on Iceland. One of the few places on Earth people can view activity on the Mid-Atlantic Ridges.  Most of the Mid-Atlantic Ridges is deep on the ocean floor crustal plates are moving apart. The North America Plate and the Eurasian Plate are moving apart in the North Atlantic Ocean.  The African Pla

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