The 2009 Samoa–Tonga great earthquake triggered doublet


Great earthquakes (having seismic magnitudes of at least 8) usually involve abrupt sliding of rock masses at a boundary between tectonic plates. Such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks, as is commonly observed in the trench-slope region seaward of a great subduction zone thrust event1,2,3,4. The earthquake sequence addressed here involves a rare instance in which a great trench-slope intraplate earthquake triggered extensive interplate faulting, reversing the typical pattern and broadly expanding the seismic and tsunami hazard. On 29 September 2009, within two minutes of the initiation of a normal faulting event with moment magnitude 8.1 in the outer trench-slope at the northern end of the Tonga subduction zone, two major interplate underthrusting subevents (both with moment magnitude 7.8), with total moment equal to a second great earthquake of moment magnitude 8.0, ruptured the nearby subduction zone megathrust. The collective faulting produced tsunami waves with localized regions of about 12 metres run-up that claimed 192 lives in Samoa, American Samoa and Tonga. Overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries, with the triggered thrust faulting only being revealed by detailed seismic wave analyses. Extensive interplate and intraplate aftershock activity was activated over a large region of the northern Tonga subduction zone.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The Samoa–Tonga great earthquake doublet region.
Figure 2: Observed and modelled R1 STFs.
Figure 3: P-wave back-projection using the Japanese F-Net stations.
Figure 4: Surface wave modelling for simple and composite models.


  1. 1

    Christensen, D. H. & Ruff, L. J. Seismic coupling and outer rise earthquakes. J. Geophys. Res. 93, 13421–13444 (1988)

    ADS  Article  Google Scholar 

  2. 2

    Dmowska, R., Rice, J. R., Lovison, L. C. & Josell, D. Stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle. J. Geophys. Res. 93, 7869–7884 (1988)

    ADS  Article  Google Scholar 

  3. 3

    Lay, T., Astiz, L., Kanamori, H. & Christensen, D. H. Temporal variation of large intraplate earthquakes in coupled subduction zones. Phys. Earth Planet. Inter. 54, 258–312 (1989)

    ADS  Article  Google Scholar 

  4. 4

    Ammon, C. J., Kanamori, H. & Lay, T. A great earthquake doublet and seismic stress transfer cycle in the central Kuril islands. Nature 451, 561–566 (2008)

    CAS  ADS  Article  Google Scholar 

  5. 5

    Kanamori, H. Seismological evidence for a lithospheric normal faulting; the Sanriku earthquake of 1933. Phys. Earth Planet. Inter. 4, 289–300 (1971)

    ADS  Article  Google Scholar 

  6. 6

    Lynnes, C. S. & Lay, T. Source process of the great 1977 Sumba earthquake. J. Geophys. Res. 93, 13407–13420 (1988)

    ADS  Article  Google Scholar 

  7. 7

    Taylor, M. A. J., Zheng, G., Rice, J. R., Stuart, W. D. & Dmowska, R. Cyclic stressing and seismicity at strong coupled subduction zones. J. Geophys. Res. 101, 8363–8381 (1996)

    ADS  Article  Google Scholar 

  8. 8

    Lay, T. et al. The 2006–2007 Kuril Islands great earthquake sequences. J. Geophys. Res. 114 B11308 10.1029/2008JB006280 (2009)

    ADS  Article  Google Scholar 

  9. 9

    Ranero, C. R., Villaseñor, A., Phipps Morgan, J. & Weinrebe, W. Relationship between bend-faulting at trenches and intermediate-depth seismicity. Geochem. Geophys. Geosyst. 6 Q12002 10.1029/2005GC000997 (2005)

    ADS  Article  Google Scholar 

  10. 10

    Faccenda, M., Gerya, T. V. & Burlini, L. Deep slab hydration induced by bending-related variations in tectonic pressure. Nature Geosci. 2, 790–793 (2009)

    CAS  ADS  Article  Google Scholar 

  11. 11

    Earthquake. Hazards Program. Magnitude 8.1—Samoa Islands region. 〈〉 (US Geological Survey, 2009)

  12. 12

    Jaffe, B. Surprises from the deadly September 29, 2009, Samoa tsunami. 〈〉 (US Geological Survey, 2009)

  13. 13

    NOAA Center for Tsunami Research. Tsunami event—September 29, 2009 Samoa. (2009)

  14. 14

    Iida, K., Cox, D. C. & Pararas-Carayannis, G. Preliminary catalog of tsunamis occurring in the Pacific Ocean. Data Report 5, HIG-67–10, 261 (Hawaii Institute of Geophysics, University of Hawaii, 1967)

  15. 15

    Gutenberg, B. & Richter, C. F. Seismicity of the Earth and Associated Phenomena 2nd edn (Princeton University Press, 1954)

    Google Scholar 

  16. 16

    Okal, E. & Kirby, S. H. Large earthquakes and tsunamis at the Samoa corner in the context of the 2009 Samoa event. Eos 90 (52), (Fall Meet. Suppl.), abstr. U21E–2182 (2009)

  17. 17

    Ekström, G. & Nettles, M. Global Centroid-Moment-Tensor Project. 〈〉 (National Science Foundation, 2009)

  18. 18

    Kanamori, H. & Rivera, L. Source inversion of W-phase: speeding up seismic tsunami warning. Geophys. J. Int. 175, 222–238 (2008)

    ADS  Article  Google Scholar 

  19. 19

    Fujii, Y. & Satake, K. Samoa Islands Tsunami on Sep. 29, 2009. (2009)

  20. 20

    Tonini, R., Pagnoni, G., Armigliato, A. & Tinti, S. The 29th September Samoa islands tsunami: preliminary simulations based on the first focal mechanisms hypotheses and implications of uncertainties in tsunami early warning strategies. Eos 90(52), (Fall Meet. Suppl.), abstr. U21E–2185 (2009)

  21. 21

    Hill, D. P. et al. Remote seismicity triggered by the M7.5 Landers, California earthquake of June 28, 1992. Science 260, 1617–1623 (1993)

    CAS  ADS  Article  Google Scholar 

  22. 22

    Velasco, A. A., Hernandez, S., Parsons, T. & Pankow, K. Global ubiquity of dynamic earthquake triggering. Nature Geosci. 1, 375–379 (2008)

    CAS  ADS  Article  Google Scholar 

  23. 23

    Umino, N., Kono, T., Hasegawa, A. & Tamura, Y. Revisiting the 1933 off Sanriku earthquake (M8.1) by using smoked-paper seismographs. Ann. Meet. Seismol. Soc. Jpn abstr. [in Japanese] (2007)

  24. 24

    Li, X., Shao, G. & Ji, C. Rupture process of the 2009 Mw 8.1 Samoa earthquake constrained by joint inverting teleseismic body, surface waves and local strong motion. Eos (Fall Meet.) abstr. U21D–03 (2009).

  25. 25

    Scholz, C. Earthquakes and friction laws. Nature 391, 37–42 (1998)

    CAS  ADS  Article  Google Scholar 

  26. 26

    Ishii, M., Shearer, P. M., Houston, H. & Vidale, J. E. Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-net array. Nature 435, 933–936 (2005)

    CAS  ADS  Article  Google Scholar 

  27. 27

    Xu, Y., Koper, K. D., Sufri, O., Zhu, L. & Hutko, A. R. Rupture imaging of the Mw 7.9 12 May 2008 Wenchuan earthquake from back projection of teleseismic P waves. Geochem. Geophys. Geosyst. 10 Q04006 10.1029/2008GC002335 (2009)

    ADS  Article  Google Scholar 

  28. 28

    Hartzell, S. H. & Heaton, T. H. Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake. Bull. Seismol. Soc. Am. 73, 1153–1184 (1983)

    Google Scholar 

  29. 29

    Kikuchi, M. & Kanamori, H. Inversion of complex body waves. Bull. Seismol. Soc. Am. 81, 2335–2350 (1991)

    Google Scholar 

  30. 30

    Dziewonski, A. M. & Anderson, D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981)

    ADS  Article  Google Scholar 

  31. 31

    Boschi, L. & Ekström, G. New images of the Earth’s upper mantle from measurements of surface-wave phase velocity anomalies. J. Geophys. Res. 107, S1, 10.1029/2000JB000059 (2002).

    Article  Google Scholar 

  32. 32

    Kennett, B. L. N., Engdahl, E. R. & Buland, R. Constraints on seismic velocities in the earth from travel times. Geophys. J. Int. 122, 108–124 (1995)

    ADS  Article  Google Scholar 

  33. 33

    VanDecar, J. C. & Crosson, R. S. Determination of teleseismic phase arrival times using multi-channel cross correlation and least squares. Bull. Seismol. Soc. Am. 80, 150–169 (1990)

    Google Scholar 

Download references


This work made use of GMT and SAC software and Federation of Digital Seismic Networks (FDSN) seismic data. The Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS) and the F-Net and Hi-Net data centres were used to access the data. C. Ji kindly shared details of his model. Z. Duputel wrote the W-Phase software version used in this study. We thank H. Savage and E. Brodsky for discussions of frictional conditional stability. This work was supported by NSF grant EAR0635570 and USGS Award Number 05HQGR0174.

Author information




All authors contributed equally to the analysis and preparation of this paper.

Corresponding author

Correspondence to Thorne Lay.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Methods Applications, Supplementary Figures S1-16 and legends for Supplementary Movies 1 and 2. (PDF 3126 kb)

Supplementary Movie 1

Animation of P wave back-projections from 6 regional networks. (MOV 1735 kb)

Supplementary Movie 2

Animation of the USGS located aftershock sequence. (MOV 4085 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Lay, T., Ammon, C., Kanamori, H. et al. The 2009 Samoa–Tonga great earthquake triggered doublet. Nature 466, 964–968 (2010).

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.