[SCG57-P03] Frictional properties of greenstone: Effects of the seamount subduction on faulting at the subduction zone
Keywords:seamount, frictional strength, greenstone
We conducted friction experiments on gouges of a greenstone from the Akiyoshi terrane in Yamaguchi, where a huge seamount with Carboniferous to Permian limestone accreted during the Permian time (e.g., Sano, 2006). Thin layer of greenstone underlying the limestone is distributed over 10 km along a fault. Experiments were performed at slip velocities of 0.0013 to 1.3 m/s, normal stresses of 0.7 to 4.0 MPa, and wet but drained conditions, using a rotary-shear apparatus installed at AIST.
At a slip velocity of 1.3 m/s, typical slip-weakening behavior was observed; friction coefficient µ rapidly increased at the onset of sliding and then progressively decreased to ~0.1 with displacement. Steady-state friction coefficient µss at this velocity clearly decreases with increasing normal stress. µss is high up to ~0.7 at low velocities, and decreases to ~0.1 at a seismic slip velocity of 1.3 m/s. The sample deformed at this high velocity shows a clear localized shear zone, whereas the sample deformed at a low velocity does not. µss of the Akiyoshi greenstone is higher than µss of typical subduction zone materials especially at low velocities; µss of sediments at the Tohoku subduction zone is <0.2 (Sawai et al., 2014) and µss of those at the Nankai Trough is <0.4 (Tsutsumi et al., 2011). Hence a seamount possibly acts as a barrier for rupture propagation due to its high frictional strength.