Trying to Link Tremor Catalogs to Numerical Models of Slow Slip

Abstract:

Recent high-resolution tremor catalogs exhibit many enigmatic features related to rapid secondary fronts arising at or behind the main, slower tremor front. These include: “Rapid tremor reversals” that progress from km-scale affairs occurring too frequently to be tidally modulated to large (10’s of km) events that clearly are tidally modulated; relatively narrow tremor “streaks” that most often follow the main tremor front, even when that front is curved; other narrow streaks that propagate a few km behind the main front; and a tremor reversal that is spawned when two streaks propagating along the main front (nearly) collide. Most “reversals” differ from most “streaks” in that the reversals, propagating mostly along strike, typically have a resolvable down-dip extent, while the streaks, propagating mostly along dip, typically do not have a resolvable along strike extent. However, some “streaks” propagating along-dip at the main front appear to have a resolvable along-strike extent; these, and the streaks that arise behind the main front, seem to argue against the streaks’ rapid velocity resulting simply from the main front intersecting a linear array of tremor sources.

The above observations, tremor amplitude trends, and the widths of propagating tremor fronts are all potential constraints on the constitutive law for slow slip. Some of these observations were reproduced by an ad-hoc two-state-variable friction law [Rubin, 2011]; some appear to have been reproduced more naturally by heterogeneous single-state variable simulations [Luo and Ampuero, AGU 2011; 2012]; some were reproduced by the simplified rate-state simulations of Collela et al. [2012]. Given the complexity of these models and the underling equations, we report here on the results of models in which a single tremor source perturbs an otherwise homogenous slow slip front propagating along a 1-D or 2-D rate-state-friction fault. The hope is that these toy models will ultimately help us to distinguish between proposed constitutive laws for slow slip.