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Collision Zones and Convergent Margins

 

Continental crust is formed, deformed and destroyed at convergent plate margins and collision zones. Subduction of plates at convergent margins is one of the most fundamental geological processes happening on Earth that contributes, in a long run, to continental growth and magmatic accretion in island arcs and, in places, to continental erosion. Subduction zones are complex, dynamic systems in which the thermal, hydraulic, and mechanical properties of the converging plates rapidly evolve in time and space. It is believed that most of the downwelling in Earth's large scale mantle convection system takes place at subduction zones. There, one of the most life-threatening geological phenomena occurs: huge earthquakes on subduction megathrusts, including the 2004 Sumatra-Andaman earthquake (Mw 9.0, with the associated devastating tsunami), the 1960 Southern Chile earthquake (M 9.5), the 1964 Alaska earthquake (M 9.2), and the 1923 Kanto earthquake (M 7.9) that destroyed Tokyo, the capital of Japan. Accompanying geohazards include tsunamis, landslides, powerful volcanic eruptions, and other threats to human life, infrastructure and economics, and to ecosystems. Given that 60% of Earth's population lives within the frontal 50 km of the coast, there is a strong need for scientific and economic efforts, to shed light on the processes responsible for such ocean margin geohazards as well as their mitigation. Scientific drilling has a high potential to such studies and must be an integral and indispensable part of this effort.

(by Jan H. Behrmann & Yang Yingsui, 2005)