Locations include the Great Rift Valley area of Africa, the Lake Baikal area of Russia, and Tibet. Some are related to the buildup of stress due to continental rifting or the transfer of stress from other regions, and some are not well understood. Click the image for terms of use.Įarthquakes are also relatively common at a few locations away from plate boundaries. Source: Lisa Christiansen, Caltech Tectonics Observatory (2008) view source. Wide bands of scattered earthquakes mark continent-continent convergent margins (e.g., between the Indian and Eurasian plates), or continental rift zones (e.g., in eastern Africa). Wider bands with earthquakes at a range of depths are subduction zones. Narrow bands with shallow earthquakes (marked in red) indicate transform boundaries or mid-ocean ridge divergent boundaries. Bands of earthquakes mark tectonic plates. Figure 12.16 Earthquakes greater than magnitude 5, from 2000 to 2008. Wide swaths of scattered earthquakes may also correspond to continental rift zones, such as in eastern Africa. Wide swaths of scattered earthquakes may correspond to continent-continent collision zones, such as between the Eurasian plate and the African, Arabian, and Indian plates to the south. Bands of earthquakes are wider along subduction zones because they take place throughout the subducting slab that extends beneath the opposing plate. Subduction zones have earthquakes at a range of depths, including some more than 700 km deep. Mid-ocean ridges and transform margins have shallow earthquakes (usually less than 30 km deep), in narrow bands close to plate margins. The depths of earthquakes, and the width of the band, depend on the type of plate boundary. This is basically how a tsunami is generated.Bands of earthquakes trace out plate boundaries (coloured dots, Figure 12.16). Now if you hold the book with its flat side on the surface of the water and move the book up and down in the water, you should generate some big waves as the vertical motion you've imposed on the water column is transferred to horizontal motion as the wave travels away from the source. If you dip the book into the bathwater spine-first and move the book back and forth longways, what do you observe? Not much, except you've ruined your book. Picture this: You have a bathtub full of water and a hard-backed book. If an earthquake happens far away from a body of water, it probably won't disturb the water too much. For an earthquake to generate a tsunami you need: Earthquakes and tsunami generationĮarthquakes happen when plates move with respect to each other because the friction and stress at the edges of plates prevent them from slipping smoothly at their boundaries. Geological Survey, the Smithsonian Institution, and the U.S. Vigil from This Dynamic Planet - a wall map produced jointly by the U.S. The Cascadia subduction zone in the US Pacific Northwest is a convergent boundary. At convergent boundaries, plates move toward each other.The Mid-Atlantic Ridge is a divergent boundary. At divergent boundaries, plates move away from each other.The San Andreas fault in California occurs at this type of plate boundary. At transform boundaries, two plates slide past each other.There are three distinct types of plate boundaries, shown illustrated by the drawing below both as separate block diagrams as well as situated within their appropriate geologic environment. This motion is driven by the flow of the mantle rock beneath the plates and by the forces plates exert at their boundaries where they touch each other. The Earth's lithosphere is broken up into a bunch of discrete pieces, called plates, that move around the surface of the planet. **Shameless plug alert**: For an in-depth look at the history of the theory of plate tectonics, take EARTH 520. In fact, my freshman advisor in college wrote the benchmark paper that outlined the mathematical model of plate tectonics, so in a sense, I'm only one "generation" removed from the pre-plate tectonics era. Plate tectonics is the Grand Unifying Theory of geosciences, but it's actually not that old. So, we'll start with the world's briefest review of plate tectonics. Earthquakes and volcanoes generate the great majority of tsunamis, and the theory of plate tectonics explains the cause of earthquakes and volcanoes. If we are going to attempt to assess the risk of a tsunami at some particular place on the planet, we must first understand how to make a tsunami.
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