The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide


Large earthquakes trigger very small earthquakes globally during passage of the seismic waves and during the following several hours to days1,2,3,4,5,6,7,8,9,10, but so far remote aftershocks of moment magnitude M ≥ 5.5 have not been identified11, with the lone exception of an M = 6.9 quake remotely triggered by the surface waves from an M = 6.6 quake 4,800 kilometres away12. The 2012 east Indian Ocean earthquake that had a moment magnitude of 8.6 is the largest strike-slip event ever recorded. Here we show that the rate of occurrence of remote M ≥ 5.5 earthquakes (>1,500 kilometres from the epicentre) increased nearly fivefold for six days after the 2012 event, and extended in magnitude to M ≤ 7. These global aftershocks were located along the four lobes of Love-wave radiation; all struck where the dynamic shear strain is calculated to exceed 10−7 for at least 100 seconds during dynamic-wave passage. The other M ≥ 8.5 mainshocks during the past decade are thrusts; after these events, the global rate of occurrence of remote M ≥ 5.5 events increased by about one-third the rate following the 2012 shock and lasted for only two days, a weaker but possibly real increase. We suggest that the unprecedented delayed triggering power of the 2012 earthquake may have arisen because of its strike-slip source geometry or because the event struck at a time of an unusually low global earthquake rate, perhaps increasing the number of nucleation sites that were very close to failure.

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Figure 1: The 2012 M = 8.6 mainshock and M = 8.2 aftershock fault ruptures and maps of strain duration τ strain at a threshold value of 0.1 microstrain.
Figure 2: Global rates of shallow (depth, ≤100 km) M  ≥ 5.5 earthquakes during the 10 d preceding and following a mainshock.
Figure 3: Cumulative number of global M  ≥ 4.5 events of depth ≤100 km during the 6 d before and after the 2012 event.
Figure 4: Global seismicity rates during the 7.3 yr between the 2004 Sumatra earthquake and the 2012 east Indian Ocean earthquake.


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Epicentres and magnitudes of seismic events were obtained from the NEIC catalogue. Seismic waveform data presented in Supplementary Information were obtained from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center. We thank T. Hanks, R. Harris, A. Michael, T. Parsons and P. Stark for their comments on a preliminary draft. V.S. works under contract at the US Geological Survey.

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F.F.P. initiated the study and performed all seismic-wave analysis. F.F.P., R.S.S. and V.S. contributed equally to earthquake catalogue analysis. All authors discussed the results and helped write the manuscript.

Corresponding author

Correspondence to Fred F. Pollitz.

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The authors declare no competing financial interests.

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Pollitz, F., Stein, R., Sevilgen, V. et al. The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide. Nature 490, 250–253 (2012).

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