Publication Date:
2006
Description:
The Sumatra-Andaman earthquake of 26 December 2004 is the first giant
earthquake (moment magnitude Mw 〉 9.0) to have occurred since the advent of
modern space-based geodesy and broadband seismology. It therefore provides an
unprecedented opportunity to investigate the characteristics of one of these enormous
and rare events. Here we report estimates of the ground displacement associated with
this event, using near-field Global Positioning System (Global Positioning System)
surveys in northwestern Sumatra combined with in situ and remote observations of the
vertical motion of coral reefs. These data show that the earthquake was generated by
rupture of the Sunda subduction megathrust over a distance of 〉1,500 kilometres
and a width of 〈150 kilometres. Megathrust slip exceeded 20 metres offshore
northern Sumatra, mostly at depths shallower than 30 kilometres. Comparison of the
geodetically and seismically inferred slip distribution indicates that approx30 per cent
additional fault slip accrued in the 1.5 months following the 500-second-long seismic
rupture. Both seismic and aseismic slip before our re-occupation of Global Positioning
System sites occurred on the shallow portion of the megathrust, where the large Aceh
tsunami originated. Slip tapers off abruptly along strike beneath Simeulue Island at the
southeastern edge of the rupture, where the earthquake nucleated and where an Mw = 7.2
earthquake occurred in late 2002. This edge also abuts the northern limit of slip in the
28 March 2005 Mw = 8.7 Nias-Simeulue earthquake
Keywords:
Earthquake
;
Fault zone
;
Subduction zone
;
Plate tectonics
;
Global Positioning System
;
Crustal deformation (cf. Earthquake precursor: deformation or strain)
;
Seismicity
;
Sumatra
;
Banda
;
Aceh
;
Andaman
;
Indonesia
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