Earthquake zones were discovered by scientists studying thousands of earthquakes worldwide after the seismograph was invented. They found that most earthquakes occur in earthquake bands that surround crustal plates.
The map below shows bands of earthquakes larger than 4.5. If you look at a map of the tectonic plates you will see that almost all the earthquakes are on the edges plates.
Earthquake zones where earthquakes occur USGS
Recording earthquakes with seismographs
Over the years millions of earthquakes have been recorded on seismographs. Using data from seismographs scientists were able to find the focus and epicenters of the earthquakes.
Scientists found that the patterns of the earthquakes were around large blocks of land that are today called tectonic plates or crustal plates. The discovery of these zones led to the Theory of Plate Tectonics.
Scientists using sonar after World War II found that a great mountain chain ran down the middle of the Atlantic Ocean. They called the mountain range the Mid-Atlantic Ridge.
Global mid-ocean ridges
Further studies of the ocean floors found that this ridge was just part of a global mid-ocean ridge system. It is approximately 84,000 km long. It is a nearly continuous mountain range that snakes across the Earth's surface like the seams on a baseball.
Low magnitude earthquakes
Mid-ocean ridges are found in all the oceans on Earth. They form at divergent boundaries where crustal plates are separating.The mid-ocean ridges are places where low magnitude earthquakes occur as new ocean floor forms on the Earth's surface.
Around the Pacific Ocean basin is a series of subduction zones. Subduction zones that surround the Pacific Ocean are zones where great earthquakes of 9.0 and higher occur.
Pacific Ocean basin
Approximately eighty percent of all recorded earthquakes originate around the Pacific Ocean basin and seventy-five percent of the active volcanoes are located in the area.
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