October 4, 2018 @ 4:00 pm - 5:00 pm CDT
Current Research in EEPS Seminar: An Yin – UCLA
Abstract Title: Water hammers tectonic tremors during slow earthquakes at plate
In this talk I show that rapid (~100 km/hour) dip-parallel (= slip-parallel) migration of tectonic tremors at seismic-aseismic transition depths (15-55 km) along a subduction shear zone can result from pressure-wave propagation in an anisotropic viscoplastic shear zone. The shear-zone anisotropy is characterized by widely spaced (>10s km) slip-parallel conduits composed of high-strength and high-permeability brittle mafic rocks embedded in low-strength and low-permeability ductile felsic materials. According to the results of recent experimental results, mafic and felsic rocks both experience compaction rather than dilation during semi-brittle deformation, which requires permeability reduction. Along a slow-slip shear zone, deformation induced rock compaction could lead to partial or complete blockage of a mafic fluid-flow conduit, leading to pressure wave propagation through the well-known water-hammer effect in hydraulics. The propagating wave with an elevated pore-fluid pressure should cause shear-zone weakening, which in turn triggers propagating shear-zone failure expressed as migrating tectonic tremors along the conduit. For a shear zone with its mafic conduits having a permeability of 10-15 m2 to 10-13 m2 and a pore-fluid viscosity of 10-5 Pa s to 10-4 Pa s, the water-hammer model proposed in this study is capable of generating a pressure jump of up to 50 kPa, sufficient to initiate tectonic tremors along subduction slow-slip shear zones. The model not only explains the observed fast along-dip tremor propagation and rapid tremor reversals, but also provides a mechanism for the observed back-and-forth tremor migration along the same paths during a slow-slip event.