A Seismic Investigation into
the earthquake that caused the Boxing Day 2004 Tsunami
Tim Bunting,
Martin Bayly (WesternGeco), Osamu Osawa, (Schlumberger K. K), Dr
Satish Singh, Helene Carton (IPGP), Phil Christie(Sclumberger
Cambridge Research), Nugroho Hananto (LIPI, IPGP), Djoko Hartoyo (BPPT)
On December 26, 2004, off the coast of Northern Sumatra, a massive
offshore earthquake triggered the deadliest Tsunami in recorded
history. The earthquake occurred at 30 km depth, measuring to 9.3 on
the open ended Richter scale. The earthquake was the second largest
earthquakemeasured, and broke 1300 km’s of plate boundary over a 150
km wide area. The initial shock lasted for 500 seconds, with
multiple and widespread aftershocks until the second earthquake
occurred some months later.
The
sudden vertical rise of the seabed, approximately 3 m, during the
earthquake displaced massive volumes of water and resulted in a
Tsunami that struck the coastlines of the Indian Ocean.
The wave
height at the shore line has been estimated to vary between 3 and
30m depending on location and extended as far as 1 kilometer
in-land. The Tsunami traveled as far as 5000km’s, to the east coast
of Africa, arriving with enough force to kill people and destroy
property.
By the
end of the day more than 150,000 people were dead or missing and
millions more were homeless in 11 countries. Hardest hit were
Sumatra (death toll greater than 170,000), Sri Lanka (death toll
greater than 31,000), Thailand, and India.
Following
this disaster Schlumberger contributed the M/V Geco Searcher and
data processing resources to create 2D seismic images in the
vicinity of the earth quake epicentre. (see map) as part of an
International research effort, in conjunction with IPGP and BPPT.
This deep seismic survey is a part of a larger effort to map the
region, since the Tsunami, including high resolution sea bottom
bathymetry mapping and an OBS refraction survey.
The data
was acquired over 5 days in July 2006 and processed in WesternGeco
Jakarta Data Centre during August to December 2006.
The data
was recorded with deep towed sources & cables, up to 12 Kilometre
offsets and twenty second recording time. Final processed images
will be shown indicating the subduction zone at 30-40 kilometres
depth.
The paper
will describe:
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The
geologic background to the area
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The
survey design process, with a focus on deep/low frequency signal
penetration
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The
reconfiguration of the Q-Marine equipment to a deep crustal
imaging system.
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The
raw data.
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Data
processing challenges
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The
final migrated images.
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Review of what has been discovered
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Potential further work
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