Crust and upper-mantle seismic anisotropy variations from the coast to inland in central and Southern Mexico (2): correlations with tectonic tremor

Abstract

Seismic anisotropy in the flat slab region of Mexico is compared with tectonic tremor (TT) activity. The anisotropy is observed in three separate horizontal layers using a novel technique with receiver functions. Those layers are identified as the continental crust and the subducted flat oceanic slab and a thin (∼10 km thick) remnant mantle wedge between those two layers. The TT is located in two zones: (1) the Sweet Spot where most of the tremor is observed (∼160–180 km from the coast) and (2) the Transient Zone (∼80–110 km from the coast). Anisotropy within each layer is observed to be different within each of the tremor zones than just outside them. The changes are explained as due to hydration within those zones. Water releasing phase changes have previously been modelled to occur within those two zones in the subducted slab (Manea & Manea). Water rising through each of the layers should generate the observed differences in anisotropy in those zones as the fast polarization direction and split times can differ between dry and hydrated material. This observation also correlates with the many observations of high pore fluid pressure associated with TT.