Not a 'rate-and-state' Theory of Friction: Application to Slow Slip Events

Abstract:

A new approach for description of dry macroscopic friction has been recently developed [1-3]. All parameters included in the model have a clear physical meaning derived from the elastic and plastic parameters of the materials in contact and the geometry of the contact surfaces. An important feature of this model is its universality allowing consideration of seismic events ranging from regular earthquakes to slow slip events [3-6]. According to this model, non-volcanic tremor is a reflection of resonant-type oscillations excited in a fault at certain depth ranges. A comparatively small effective normal stress (hence a high fluid pressure) is required to make the model consistent with observed tremor parameters. Tremor may be triggered by local small-scale failure such as a regular earthquake, low frequency earthquake (LFE), very low frequency earthquake, or aseismic slip. In episodic tremor and slip events a moving slip pulse generates tremor due to interaction with structural heterogeneities in a fault and also to failures of small asperities. Observed tremor parameters, such as central frequency and frequency attenuation curve, are associated with fault parameters and conditions, such as elastic modulus, effective normal stress, penetration hardness, and friction. In the framework of this model it is possible to explain the complicated pattern of tremor migration, including rapid tremor propagation and reverse tremor migration. Our model indicates that tremor is not necessarily a superposition of LFEs, as is commonly assumed.

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