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Non-volcanic tremor and low-frequency earthquake swarms


Non-volcanic tremor is a weak, extended duration seismic signal observed episodically on some major faults, often in conjunction with slow slip events1,2,3,4. Such tremor may hold the key to understanding fundamental processes at the deep roots of faults, and could signal times of accelerated slip and hence increased seismic hazard. The mechanism underlying the generation of tremor and its relationship to aseismic slip are, however, as yet unresolved. Here we demonstrate that tremor beneath Shikoku, Japan, can be explained as a swarm of small, low-frequency earthquakes, each of which occurs as shear faulting on the subduction-zone plate interface. This suggests that tremor and slow slip are different manifestations of a single process.

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Figure 1: Comparison of LFE, slow slip event, and megathrust earthquake mechanisms.
Figure 2: Comparison of earthquake/LFE/tremor spectra.
Figure 3: Example of a detected LFE.
Figure 4: Detection of LFE swarms forming tremor.


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This material is based upon work supported by the National Science Foundation. We thank S. Nakamula for assistance with the Hi-net data. All data were obtained from the NIED Hi-net data server.

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Correspondence to David R. Shelly.

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Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Figures S1-S2 with Legends, Legends for Supplementary Movies 1 and 2 and an additional reference. (PDF 589 kb)

Supplementary Movie 1

This file contains Supplementary Movie 1. The movie shows low-frequency earthquake detections composing tremor on September 2, 2005, 19:00-20:00. (MOV 2343 kb)

Supplementary Movie 2

This file contains Supplementary Movie 2. The movie shows low-frequency earthquake detections composing tremor on August 29, 2005, 17:00-18:00. (MOV 2509 kb)

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Shelly, D., Beroza, G. & Ide, S. Non-volcanic tremor and low-frequency earthquake swarms. Nature 446, 305–307 (2007).

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