Tectonic Tremor as Friction-Induced Inertial Vibration

Kyungjae Im, & Jean-Philippe Avouac

Published August 9, 2021, SCEC Contribution #11220, 2021 SCEC Annual Meeting Poster #133

Slow slip events are often accompanied by a tremor but how the tremor is generated is yet elusive. In this study, we test the possibility that it is an inertial vibration. In the case of a single-degree-of-freedom spring and slider system with mass per unit area M, governed by rate-and-state friction with effective normal stress σ’, excitation of inertial vibrations is primarily dependent on the inertial number η = MV^2/σ’aDc>1, where a and Dc characterize the friction law. Accordingly, a tremor can be excited in a low effective normal stress (σ’) zone, for example, in a zone of high pore pressure, when the loading rate (Vl) is temporally increased, as can happen during a slow slip event. A high loading rate help sustain the vibration, but a long-lasting attenuating tremor can still be excited even with a moderate velocity perturbation as long as the normal stress is sufficiently small. We use numerical simulations to verify that this hypothesis holds for a one-dimensional fault. The dominant frequency of the tremor is close to the fundamental frequency of resonance of the frictionless shear crack at a low sliding rate. Higher frequency modes are excited at higher sliding velocity. We show simulations of spontaneous slow slip events associated with tremor radiated from inertial vibration of a fault patch with locally low effective normal stress. This model provides a possible explanation for tectonic tremors associated with slow slip events.

Key Words
tremor, slow slip, friction

Citation
Im, K., & Avouac, J. (2021, 08). Tectonic Tremor as Friction-Induced Inertial Vibration. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)