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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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.


  1. 1

    Obara, K. Nonvolcanic deep tremor associated with subduction in southwest Japan. Science 296, 1679–1681 (2002)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Rogers, G. & Dragert, H. Episodic tremor and slip on the Cascadia subduction zone: The chatter of silent slip. Science 300, 1942–1943 (2003)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Nadeau, R. M. & Dolenc, D. Nonvolcanic tremors deep beneath the San Andreas fault. Science 307 389 (2005) published online 9 December 2004 (doi:10.1126/science.1107142).

    CAS  Article  PubMed  Google Scholar 

  4. 4

    Obara, K., Hirose, H., Yamamizu, F. & Kasahara, K. Episodic slow slip events accompanied by non-volcanic tremors in southwest Japan subduction zone. Geophys. Res. Lett. 31 doi: 10.1029/2004GL020848 (2004)

  5. 5

    Katsumata, A. & Kamaya, N. Low-frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan. Geophys. Res. Lett. 30 doi: 10.1029/2002GL015981 (2003)

  6. 6

    Shelly, D. R., Beroza, G. C., Ide, S. & Nakamula, S. Low-frequency earthquakes in Shikoku, Japan and their relationship to episodic tremor and slip. Nature 442, 188–191 (2006)

    ADS  CAS  Article  Google Scholar 

  7. 7

    Ide, S., Shelly, D. R. & Beroza, G. C. Mechanism of deep low frequency earthquakes: further evidence that deep non-volcanic tremor is generated by shear slip on the plate interface. Geophys. Res. Lett. 34 doi: 10.1029/2006GLO28890 (2007).

  8. 8

    Gibbons, S. J. & Ringdal, F. The detection of low magnitude seismic events using array-based waveform correlation. Geophys. J. Int. 165, 149–166 (2006)

    ADS  Article  Google Scholar 

  9. 9

    Dragert, H., Wang, K. & Rogers, G. Geodetic and seismic signatures of episodic tremor and slip in the northern Cascadia subduction zone. Earth Planets Space 56, 1143–1150 (2004)

    ADS  Article  Google Scholar 

  10. 10

    Kao, H. et al. Spatial-temporal patterns of seismic tremors in northern Cascadia. J. Geophys. Res. 111 doi: 10.1029/2005JB003727 (2006)

  11. 11

    Kao, H. et al. A wide depth distribution of seismic tremors along the northern Cascadia margin. Nature 436, 841–844 (2005)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Dodge, D. A., Beroza, G. C. & Ellsworth, W. L. Detailed observations of California foreshock sequences: implications for the earthquake initiation process. J. Geophys. Res. 101, 22371–22392 (1996)

    ADS  Article  Google Scholar 

  13. 13

    McGuire, J. J., Boettcher, M. S. & Jordan, T. H. Foreshock sequences and short-term earthquake predictability on East Pacific Rise transform faults. Nature 434, 457–461 (2005)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Vidale, J. E. & Shearer, P. M. A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations. J. Geophys. Res. 111 doi: 10.1029/2005JB004034 (2006)

  15. 15

    Hirose, H. & Obara, K. Repeating short- and long-term slow slip events with deep tremor activity, around the Bungo channel region, southwest Japan. Earth Planets Space 57, 961–972 (2005)

    ADS  Article  Google Scholar 

  16. 16

    Ando, M. A fault model of the 1946 Nankaido earthquake derived from tsunami data. Phys. Earth Planet. Int. 28, 320–336 (1982)

    ADS  Article  Google Scholar 

Download references


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.

Author information



Corresponding author

Correspondence to David R. Shelly.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

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)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

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

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing