[J06-3] The spectrum of fault-zone deformation processes (from slow slip to earthquake) III

[J06-3-01] Rapid Tremor Migration Induced by Pore Pressure Waves

^○Victor M. Cruz-Atienza¹, Carlos Villafuerte¹, Harsha Bhat² (1.Instituto de Geofisica, UNAM, Mexico, 2.Ecole Normale Superieur, Paris, France)

Observations in different subduction zones suggest that overpressured fluids close to the plate interface may be linked to the origin of tectonic tremors (TT) and low frequency earthquakes (LFE). Fluids at nearly lithostatic pressures within the top few kilometers of the oceanic crust have been inferred in several subduction zones, including the state of Guerrero, Mexico. The actual effect of fluid diffusion on fault zones may strongly affect the seismicity rate by inducing transient changes in the effective fault-normal stresses. These changes propagate slowly (i.e., ~50 meters per day or 0.002 km/h) during fluid-injection tests in the upper crust. However, when fluids are subject to nearly lithostatic pressures at depth (i.e., ~40 km), small pore pressure gradients may induce large transient variations of the permeability that, under some conditions, produce solitary pressure waves propagating much faster across the fault zone. Recent TT epicentral locations in Guerrero using the Tremor Energy and Polarization (TREP) method (Cruz-Atienza et al., JGR, 2015) show that sources of these events migrate with speeds ranging between 10 and 80 km/h during slow slip events (SSE). Migration directions change with time, so they are first parallel to the slow slip front as observed in other subduction zones. However, latter migration directions are different and consistent with the pore pressure gradient induced by the slow slip, as predicted by our poroelastic modeling of SSEs in Guerrero. A parametric study of the governing non-linear diffusion equation shows that pore pressure waves propagate, under realistic conditions (as settled by experimental rock tests), with the same speeds as those observed for the rapid tremor migrations (RTM) in Guerrero, Cascadia and Japan. This result suggests that physical conditions surrounding the plate interface (such as pore pressure gradients) are likely to produce pressure waves, and that these waves may be responsible for the RTM.