RV Sonne Cruise 200, 11 Jan-11 Mar 2009. Jakarta - Jakarta

Abstract

All plate boundaries are divided into segments - pieces of fault that are distinct from one
another, either separated by gaps or with different orientations. The maximum size of an
earthquake on a fault system is controlled by the degree to which the propagating rupture can
cross the boundaries between such segments. A large earthquake may rupture a whole segment
of plate boundary, but a great earthquake usually ruptures more than one segment at once.
The December 26th 2004 MW 9.3 earthquake and the March 28th 2005 MW 8.7 earthquake
ruptured, respectively, 1200–1300 km and 300–400 km of the subduction boundary between
the Indian-Australian plate and the Burman and Sumatra blocks. Rupture in the 2004 event
started at the southern end of the fault segment, and propagated northwards. The observation
that the slip did not propagate significantly southwards in December 2004, even though the
magnitude of slip was high at the southern end of the rupture strongly suggests a barrier at that
place. Maximum slip in the March 2005 earthquake occurred within ~100 km of the barrier
between the 2004 and 2005 ruptures, confirming both the physical importance of the barrier,
and the loading of the March 2005 rupture zone by the December 2004 earthquake.
The Sumatran Segmentation Project, funded by the Natural Environment Research Council
(NERC), aims to characterise the boundaries between these great earthquakes (in terms of both
subduction zone structure at scales of 101-104 m and rock physical properties), record seismic
activity, improve and link earthquake slip distribution to the structure of the subduction zone
and to determine the sedimentological record of great earthquakes (both recent and historic)
along this part of the margin. The Project is focussed on the areas around two earthquake
segment boundaries: Segment Boundary 1 (SB1) between the 2004 and 2005 ruptures at
Simeulue Island, and SB2 between the 2005 and smaller 1935 ruptures between Nias and the
Batu Islands.
Cruise SO200 is the third of three cruises which will provide a combined geophysical and
geological dataset in the source regions of the 2004 and 2005 subduction zone earthquakes.
SO200 was divided into two Legs. Leg 1 (SO200-1), Jakarta to Jakarta between January 22nd
and February 22nd, was composed of three main operations: longterm deployment OBS
retrieval, TOBI sidescan sonar survey and coring. Leg 2 (SO200-2), Jakarta to Jakarta between
February 23rd and March 11th, was composed of two main operations: Multichannel seismic
reflection (MCS) profiles and heatflow probe transects.

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Identifiers

ORCID for L.C. McNeill: orcid.org/0000-0002-8689-5882

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