Teleseismic Imaging Reveals Fluid Pathways Governing Tectonic Tremor Genesis in the Central Mexico Flat-Slab Subduction Zone

Tectonic tremors in subduction zones are commonly attributed to shear slip along the plate interface, but their potential link to fluid processes in the overriding crust remains debated. Here, we apply a novel elastic reverse-time migration method to teleseismic waveforms recorded by a quasi-linear dense seismic array in central Mexico to image subsurface fluid pathways with unprecedented resolution. Our results reveal two vertically oriented discontinuities featured with negative amplitudes—interpreted as low-velocity fluid-filled fracture networks—that connect the subducting Cocos slab to tremor source regions in the overriding plate to facilitate fluid migration upwards from slab dehydration. These fracture zones are spatially correlated with both northern and southern tremor clusters of the well-known “sweet spot.” It is also observed that some tremors have harmonic spectra, further supporting they are related to fluid resonance in the fracture zones of overriding plate. The findings demonstrate that crustal fractures, not only interface slip, govern tremor generation in weakly coupled flat slab systems. These findings redefine fluid-mediated tremor mechanisms in this flat-slab subduction zone and make it necessary to reassess seismic hazards in regions where deep fluid fluxes interact with overriding plate faults.