title: The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide.
abstract: Large earthquakes trigger very small earthquakes globally during passage of the seismic waves and during the following several hours to days, but so far remote aftershocks of moment magnitude M ≥ 5.5 have not been identified, 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 away. 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.
authors.affiliation: US Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025, USA. fpollitz@usgs.gov
authors.forename: Fred F
authors.initials: FF
authors.lastname: Pollitz
authors.forename: Ross S
authors.initials: RS
authors.lastname: Stein
authors.forename: Volkan
authors.initials: V
authors.lastname: Sevilgen
authors.forename: Roland
authors.initials: R
authors.lastname: Bürgmann