Modeling non-volcanic tremor, slow slip events and earthquakes with space-variable frictional weakening and creep

Abstract:

Non Volcanic Tremor (NVT) and related slow slip events (SSE) are observed below the seismogenic sections of numerous subduction zones and several major strike-slip faults. The NVT events have multiple characteristics that distinguish them from regular earthquakes. A frictional fault in elastic solid with (near-)zero effective weakening during slip produces failure avalanches associated with a second-order (critical) transition in the state of the interface referred to as critical depinning transition [Fisher et al., PRL, 1997]. The critical slip events have properties and scaling relations that characterize observed NVT [Ben-Zion, GJI, 2012]. A reduction of dynamic weakening with depth toward zero around the brittle-ductile transition provides a simple generic explanation for the occurrence of NVT below the seismogenic zone and the diverse phenomena that distinguish NVT from regular earthquakes. SSE may be generated by large NVT that saturate the narrow dimension of the critical section of the interface, or by a fault section with elevated creep properties. The results imply that NVT have little predictive power on large events in the overriding seismogenic zone. In addition to explaining observed results, the model makes further predictions that may be tested with future observations. These include fractal slip distributions, discrete power law frequency-moment statistics with exponent 3/2 and exponential tapering, overall scale-invariant time histories, triggered periodic NVT with evolving size and rate correlated with the stressing rate of the periodic triggering mechanisms, and parabolic (or exponential) source time functions for event sizes measured by duration (or moment/potency). A model configuration tailored with dimensions, rheological properties and boundary conditions to the Guerrero segment of the Mexican subduction zone can explain multiple features of NVT, SSE, earthquakes and triggered events in that region [Zigone et al., GJI, 2015].