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The June 2000 Mw 7.9 earthquakes south of Sumatra: Deformation in the IndiaAustralia Plate

Summary: The June 2000 Mw 7.9 earthquakes south of Sumatra: Deformation in
the India­Australia Plate
Rachel E. Abercrombie,1,2
Michael Antolik,1
and Go¨ran Ekstro¨m1
Received 15 June 2001; revised 19 July 2002; accepted 23 October 2002; published 11 January 2003.
[1] Two large (Mw 7.9) earthquakes occurred on 4 and 18 June 2000, south of Sumatra,
beneath the Indian Ocean. Both earthquakes were predominantly left-lateral strike-slip on
vertical N-S trending faults that we interpret to be reactivated fracture zones. The 4 June
Enggano earthquake occurred at the edge of the rupture area of the 1833 subduction
earthquake. The first strike-slip subevent within the subducting plate triggered a thrust
subevent on the plate interface, which comprised at least 35% of the total moment and
ruptured SE away from the 1833 earthquake. The 18 June earthquake in the Wharton
Basin is one of the largest shallow strike-slip faulting earthquakes ever recorded. A small
second subevent with reverse slip is required to fit the body waves. The orientation of both
subevents in our preferred model is consistent with the current stress field in the region.
Both the June 2000 earthquakes are consistent with recent models of distributed
deformation in the India­Australia composite plate. The occurrence of the Enggano
earthquake implies that the stress field within the Indian plate continues to a depth of 50
km in the subducting slab. The purely strike-slip source model of the Wharton Basin


Source: Abercrombie, Rachel E. - Department of Earth Sciences, Boston University


Collections: Geosciences