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Frictional and Lithological Controls on Shallow Slow Slip at the Northern Hikurangi Margin
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  • Srisharan Shreedharan,
  • Matt J. Ikari,
  • Clay Wood,
  • Demian M Saffer,
  • Laura Wallace,
  • Chris Marone
Srisharan Shreedharan
The University of Texas at Austin

Corresponding Author:srisharan.nitk@gmail.com

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Matt J. Ikari
University of Bremen
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Clay Wood
Penn State University
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Demian M Saffer
University of Texas at Austin
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Laura Wallace
GNS Science
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Chris Marone
Pennsylvania State University
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Slow slip events (SSEs) have been identified at subduction zones globally as an important link in the continuum between elastodynamic ruptures and stable creep. The northern Hikurangi margin is home to shallow SSEs which propagate to within 2 km of the seafloor and possibly to the trench, providing insights into the physical conditions conducive to SSE behavior. We report on a suite of friction experiments performed on protolith material entering the SSE source region at the Hikurangi margin, collected during the International Ocean Discovery Program Expedition 375. We performed velocity stepping and slide-hold-slide experiments over a range of fault slip rates, from plate rate (5 cm/yr) to ~1 mm/s and quantified the frictional velocity dependence and healing rates for a range of lithologies at different stresses. The friction velocity dependence (a-b) and critical slip distance Dc increase with fault slip rate in our experiments. We observe a transition from velocity weakening to strengthening at slip rates of ~0.3 µm/s. This velocity dependence of Dc could be due to a combination of dilatant strengthening and a widening of the active shear zone at higher slip rates. We document low healing rates in the clay-rich volcaniclastic conglomerates, which lie above the incoming plate basement at least locally, and relatively higher healing rates in the chalk lithology. Finally, our experimental constraints on healing rates in different input lithologies extrapolated to timescales of 1-10 years are consistent with the geodetically-inferred low stress drops and healing rates characteristic of the Hikurangi SSEs.
Feb 2022Published in Geochemistry, Geophysics, Geosystems volume 23 issue 2. 10.1029/2021GC010107