Diagram of subduction interface
a) Sketch of the subduction interface and transitions in structural style and seismic behavior with depth. The subduction interface has been suggested to transition down-dip near the depth of slow slip and tremor from a discrete frictional megathrust fault to a more distributed frictional-viscous shear zone, which is the basis for the model setup shown in panel [b]). b) Model setup with high viscosity inclusions (clasts) that represent strong mafic lenses embedded in a softer matrix. Credit: Behr et al., 2021, Figure 1ab
Source: AGU Advances

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. [2021] 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. [2021]. Transient Slow Slip Characteristics of Frictional-Viscous Subduction Megathrust Shear Zones. AGU Advances, 2, e2021AV000416. https://doi.org/10.1029/2021AV000416

—Tom Parsons, Editor, AGU Advances

Text © 2021. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.