In this study, I show that rapid (~100 km/h) dip-parallel tremor migration at seismic-aseismic transition depths (15–55 km) of a convergent margin can result from pressure-wave propagation in an anisotropic viscoplastic shear zone. The anisotropy is characterized by slip-parallel conduits in the dip direction composed of high-permeability brittle mafic rocks embedded in low-permeability ductile felsic materials. At the onset of a slow-slip event, the initial compaction of a mafic conduit causes permeability reduction that in turn can lead to partial or complete blockage of flow path. Due to the water-hammer effect, the sudden blockage of flow paths can trigger a propagating pressure wave with an elevated pore-fluid pressure, which is capable of initiating a progressive shear failure expressed as migrating tectonic tremors along the conduit. For a mafic conduit with a pre-slip static permeability of ~10–13 m2 and a syn-slip dynamic permeability of 10–15 m2, the water-hammer model generates a pressure jump of up to 50 kPa, sufficient to initiate tremors along subduction zones and shear-zone deformation during the same slow-slip event.
Research Article|October 23, 2018