Global Distribution of Earthquakes Earth scientists have determined that the glo

Question

Global Distribution of Earthquakes Earth scientists have determined that the global distribu- tion of earthquakes is not random but follows a few rela- tively narrow belts that wind around Earth. Figure 9 illustrates the world distribution of earthquakes for a period of several years. Use the figure to answer ques- tions 17 and 18. 17. With what Earth feature is each of the following earthquake belts associated? Western and southern Pacific Ocean basin: Western South America: Mid-Atlantic Ocean basin:

Explanation / Answer

(i) Ocean - Ocean Subduction Zone

In Western and Southern Pacific ocean basin, Ocean - Ocean Subduction zones are present mostly where older and heavier Pacific Plate (oceanic plate) subducts forming Trenches and Island Arcs.

(ii) Ocean-Continent Subduction zone

In Western South America, The Nazca Oceanic Plate is subducting beneath the South American plate (continental plate). This type of subduction is Ocean-Continent Subduction in which the heavier oceanic plate subducts beneath the lighter continental plate to form Trenches and Volcanic arcs.

These subduction zones (i) and (ii) are the regions of large magnitude, shallow to deep level earthquakes.

(iii) Mid- Atlantic Ridge

Mid- Atlantic Ridge is a Mid Oceanic Ridge. Mid oceanic ridge is the site of new oceanic crust formation. Magma plumes from the mantle rises up to the Mid Oceanic Ridge and aids in creation of new oceanic crust. Due to the formation of oceanic crust a ridge push force develops which helps in the 'sea-floor spreading'. Earthquakes are of small magnitude and are mostly shallow level earthquakes which generates during magma extrusion.

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