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6.10: Earthquakes at Convergent Plate Boundaries

  • Page ID
    5410
  • What damage is done to people's lives by earthquakes?

    In a large earthquake hundreds or thousands of people may die. Many more may lose their homes and livelihoods. After a large quake, the world's attention turns to help the victims. But soon there is another disaster in the news, and the world's attention turns. People may be left homeless due to an earthquake for many years.

    Convergent Plate Boundaries

    Earthquakes at convergent plate boundaries mark the location of the subducting lithosphere. The motion of the lithosphere as it plunges through the mantle causes the quakes (Figure below). At greater depths, the plate heats up enough to deform plastically.

    A cross section of earthquake epicenters

    A cross section of earthquake epicenters. The depth outlines the subducting plate. There are shallow, intermediate, and deep earthquakes.

    Convergent plate boundaries produce earthquakes most of the way around the Pacific Ocean basin.

    Ocean-Ocean: Japan

    Earthquakes in Japan are caused by ocean-ocean convergence. In this part of the Pacific Ocean, oceanic crust subducts beneath oceanic crust. This creates as many as 1,500 earthquakes every year.

    In March 2011, the 9.0 magnitude Tōhoku earthquake struck off of northeastern Japan. Damage from the quake was severe. Even more severe was the damage from the tsunami generated by the quake (Figure below and Figure below). A tsunami is an enormous ocean wave or set of waves generated by an underwater earthquake. In all, 25,000 people were known dead or missing.

    The damage caused in Japan from an earthquake and tsunami

    The damage in Miyako, Iwate, Japan after a 9.0 magnitude earthquake and the massive tsunami it generated struck in March, 2011.

    Here is an interactive feature article about the earthquake: http://www.nytimes.com/interactive/2011/03/11/world/asia/maps-of-earthquake-and-tsunami-damage-in-japan.html.

    The damage caused in Japan from an earthquake and tsunami

    Destruction in Ofunato, Japan, from the 2011 Tōhoku Earthquake.

    Ocean-Continent: Cascades

    The Pacific Northwest of the United States is at risk from a potentially massive earthquake. The subduction of three small plates beneath North America produces active volcanoes, the Cascades. The region also experiences earthquakes. However, large earthquakes hit only every 300 to 600 years. The last was in 1700. That quake had an estimated magnitude of around 9. A quake of that magnitude today could produce an incredible amount of destruction and untold fatalities.

    Continent-Continent: Asia

    The collision of two continents also creates massive earthquakes. Many earthquakes happen in the region in and around the Himalayan Mountains. The 2005 Kashmir, India, earthquake is responsible for about 20,000 deaths, with many more people injured or made homeless (Figure below).

    Damage from the 2005 Kashmir earthquake

    Damage from the 2005 Kashmir earthquake.

    Summary

    • Earthquakes occur all along the subducting plate as it plunges into the mantle.
    • All three types of convergent plate boundaries produce massive earthquakes.
    • Subduction zones around the Pacific Rim are responsible for many of the world's earthquakes.

    Review

    1. Why does a subducting plate produce so many earthquakes?
    2. What depths of earthquakes does a subducting plate produce?
    3. What caused the most destruction from the 2011 Japan earthquake?
    4. In the chart above of depth vs. distance of the earthquakes, what is being outlined by the dots?
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