Model of deep non-volcanic tremor part I: ambient and triggered tremor

TL;DR

This paper presents a fault dynamics model explaining deep non-volcanic tremor as an internal fault response to external triggers, predicting specific features like frequency range, emission area size, and lack of impulsive phase, challenging traditional earthquake-based views.

Contribution

It introduces a novel fault response model for tremor, emphasizing resonant oscillations and internal fault failure, expanding understanding beyond superimposed low frequency earthquakes.

Findings

Tremor frequency depends on fault failure type.

Tremor emission area is limited to a few dozen km.

Tremor can occur without impulsive seismic phases.

Abstract

There is evidence of triggering of tremor by seismic waves emanating from distant large earthquakes. The frequency contents of triggered and ambient tremor are largely identical, suggesting that tremor does not depend directly on the nature of the source. We show here that the model of plate dynamics developed earlier by us is an appropriate tool for describing the onset of tremor. In the framework of this model, tremor is an internal response of a fault to a failure triggered by external disturbances. The model predicts generation of radiation in a frequency range defined by the fault parameters. Other specific features predicted are: the upper limit of the size of the emitting area is a few dozen km; tremor accompanies earthquakes and aseismic slip; the frequency content of tremor depends on the type of failure. The model also explains why a tremor has no clear impulsive phase, in contrast to earthquakes. A comparatively small effective normal stress (hence a high fluid pressure) is required to make the model consistent with observed tremor parameters. Our model indicates that tremor is not necessarily a superposition of low frequency earthquakes, as commonly assumed, although the latter may trigger them. The approach developed complements the conventional viewpoint which assumes that tremor reflects a frictional process with low rupture speed. Essentially our model adds the hypothesis that resonant-type oscillations exist inside a fault. This addition may change our understanding of the nature of tremor in general, and the methods of its identification and location in particular.