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.

Triggered Seismic Events along the Eastern Denali Fault in Northwest Canada Following the 2012 Mw 7.8 Haida Gwaii, 2013 Mw 7.5 Craig, and Two Mw>8.5 Teleseismic Earthquakes

“…6). The Indian Ocean mainshock has triggered many microearthquakes and tremor around the world (e.g., Wu et al, 2012), as well as a transient global increase of M w ≥ 5:5 earthquakes (Pollitz et al, 2012). Its Love wave also triggered an M w 3.9 earthquake in central Alaska (Tape et al, 2013), which was recorded by stations in our study region at ∼2700 s after the Indian Ocean mainshock.…”

Limitations of rupture forecasting exposed by instantaneously triggered earthquake doublet

“…Great earthquakes commonly generate both instantaneous and delayed seismicity at distances of hundreds to thousands of kilometres, where static stress changes are negligible, but these remote aftershocks usually have small magnitudes and often occur in volcanic or geothermal areas with quite different stress and frictional regimes [34][35][36] . A notable exception was a M w 6.9 earthquake in Japan that initiated during the passage of surface waves from a M w 6.6 event in Indonesia, confirming the potential for larger triggered earthquakes in compressive environments 37 .…”

The Profound Reach of the 11 April 2012 M 8.6 Indian Ocean Earthquake: Short-Term Global Triggering Followed by a Longer-Term Global Shadow

“…We use reported moment magnitude M w . Pollitz et al (2012;their fig. S3) note that from 2002 to 2012 this catalog has a magnitude of completeness M c ∼ 4:8.…”

“…An increase at M ≥ 6:5 following the Indian Ocean event, however, is seen regardless of how the catalog is edited (e.g., part b of these figures) because these larger events are remote. A diagnostic property of the globally triggered seismicity identified by Pollitz et al (2012) was the predominance of strike-slip events, presumably because the strongest seismic energy radiated globally was transmitted by the Love waves, which have a high potential for dynamically triggering strikeslip events (Hill, 2010). Figure 4a,b shows the fraction γt of M ≥ 5:0 remote events with strike-slip focal mechanisms relative to the total number of M ≥ 5:0 remote events cumulatively up to time t, derived from the Global CMT catalog (the Global Centroid Moment Tensor Project [see Data and Resources]; Dziewonski et al, 1981;Ekström et al, 2012).…”