Convergence between tectonic plates at subduction boundaries is mostly accommodated as slip along the subduction interface thrust fault. The portion of the fault where earthquakes nucleate is known as the seismogenic zone. In the seismogenic zone the fault is thought to be locked (due to friction) during the time between earthquakes, and most of the motion between the subducting and overriding plates occurs instantaneously in major megathrust earthquakes, which include the largest earthquakes recorded on the planet. However, in some cases subduction thrust slip occurs as steady aseismic creep (without a major earthquake), and it has been recently discovered that portions of many subduction thrusts slip episodically in slow slip events (SSEs) that take weeks to years to occur [see, e.g., Schwartz and Rokosky, 2007].
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