Figures 1a and 1b show information relating to Japan and the Tohoku earthquake, 2011. Describe the tectonic setting shown in Figure 1a and relate the intensity of the Tohoku earthquake shown in Figure 1b to that setting.
Describe the characteristics, and explain the formation, of deep sea trenches and island arcs. Deep sea trenches | Island arcs | * When two oceanic plates or an oceanic and continental converge, usually the more dense crust is subducted under the less dense and lighter crust * The downwarping process of the plate forms a very deep part of the ocean known as a trench, examples include the Marianas Trench or Peru-Chile trench * Marianas Trench - the fast-moving Pacific Plate converges against the slower moving Philippine Plate * Peru-Chile trench - the Nazca plate is subducting under the South American plate * Characteristics: * Very deep, the Peru-Chile trench is over 8km deep and the Marianas trench is over 10km deep * Found along the seaward edge of destructive margins * The descending plate provides a source of stress as the two plates interact, leading to frequent earthquakes. | * When two oceanic plates converge and the more dense crust is subducted under the less dense and lighter crust * The magma that forms the Island Arcs are produced by the partial melting of the descending plate in the Benioff zone under the crust * This results in the formation of volcanoes which over millions of years pile up lava on the ocean floor * Until a submarine volcano rises above sea level to form an island volcano. * Examples include the Mariana Island and the Aleutian Islands * Characteristics: * Only happen offshore and at two seaward oceanic converging plates (destructive margin) * typically strung out in curved chains * The descending plate provides a source of stress as the two plates interact, leading to frequent