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Associated with the slab suction force is the idea of trench roll-back. As a slab of oceanic crust subducts into the mantle, the hinge of the plate (the point where the plate begins to subduct) tends to regress away from the trench. This occurs because there is effectively no force to hold the hinge in one location. [5]
Trench suction is included in this causal mechanism. Trench suction is induced by the flow of the asthenosphere in the mantle wedge area; trench suction increases with subduction velocity, a decrease of the mantle wedge thickness, or an increase in the mantle wedge viscosity. [13]
An individual trench can be thousands of kilometers long. [3] Most trenches are convex towards the subducting slab, which is attributed to the spherical geometry of the Earth. [21] The trench asymmetry reflects the different physical mechanisms that determine the inner and outer slope angle.
Slab pull is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate. In 1975 Forsyth and Uyeda used the inverse theory method to show that, of the many forces likely to be driving plate motion, slab pull was the strongest. [1]
Slab pull is therefore most widely thought to be the greatest force acting on the plates. In this understanding, plate motion is mostly driven by the weight of cold, dense plates sinking into the mantle at trenches. [8] Recent models indicate that trench suction plays an important role as well.
The backward motion of the subduction zone relative to the motion of the plate which is being subducted is called trench rollback (also known as hinge rollback or hinge retreat). As the subduction zone and its associated trench pull backward, the overriding plate is stretched, thinning the crust and forming a back-arc basin.
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Pressure at bottom of Mariana Trench, about 11 km below ocean surface (1100 bar) [75] 100 to 300 MPa 15,000 to 44,000 psi Pressure inside reactor for the synthesis of high-pressure polyethylene (HPPE) [76] 250 MPa 36,000 psi Record diesel engine common rail fuel system pressure [77] 400 MPa 58,000 psi