The onset of geodesy and seismic monitoring has produced a richer picture of slip in subduction zones that includes not only megathrust earthquakes, but also variations of slow slip events of different sizes and durations. Slow slip events can rival large earthquakes in terms of cumulative moment. Many of these slow slip events occur in the transition zone between the shallow brittle and deeper ductile regimes. Behr et al.  model this transition as a narrow zone of strong clasts embedded within a ductile matrix, as has been observed in outcrops of exhumed subduction zones (as shown in the figure above). The authors simulate slip while systematically varying strength contrasts and relative proportions of weak and strong material. They find three slip modes that result from these variations: aseismic slip with no earthquakes, slow-slip, and regular earthquakes, which mirror observations from subduction zones as well as what is observed geologically in exhumed subduction zones.
Citation: Behr, W., Gerya, T., Cannizzari, C. & Blass, R. . Transient Slow Slip Characteristics of Frictional-Viscous Subduction Megathrust Shear Zones. AGU Advances, 2, e2021AV000416. https://doi.org/10.1029/2021AV000416
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