147 research outputs found
Plate-boundary deformation associated with the great Sumatra–Andaman earthquake
The Sumatra–Andaman earthquake of 26 December 2004 is the first giant earthquake (moment magnitude M_w > 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 (GPS) 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 ~30 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 GPS 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 M_w = 7.2 earthquake occurred in late 2002. This edge also abuts the northern limit of slip in the 28 March 2005 M_w = 8.7 Nias–Simeulue earthquake
Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system
Author Posting. © Nature Publishing Group, 2007. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 450 (2007): 407-410, doi:10.1038/nature06273.Continental erosion controls atmospheric carbon dioxide levels on geological timescales
through silicate weathering, riverine transport and subsequent burial of organic carbon
in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins
is however limited by the organic carbon load capacity of the sediments and organic
carbon oxidation in continental margins. At the global scale, previous studies have
suggested that about 70 per cent of riverine organic carbon is returned to the
atmosphere, such as in the Amazon basin. Here we present a comprehensive organic
carbon budget for the Himalayan erosional system, including source rocks, river
sediments and marine sediments buried in the Bengal fan. We show that organic carbon
export is controlled by sediment properties, and that oxidative loss is negligible during
transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the
organic carbon is recent organic matter captured during transport, which serves as a
net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the
Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon
buried in oceanic sediments. High erosion rates in the Himalayas generate high
sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the
observed extreme organic carbon burial efficiency. Active orogenic systems generate
enhanced physical erosion and the resulting organic carbon burial buffers atmospheric
carbon dioxide levels, thereby exerting a negative feedback on climate over geological
timescales
Beach ridges, foredunes or transgressive dunefields? Definitions and an examination of the Torres to TramandaĂ barrier system, Southern Brazil
Results from a magnetic survey and geomagnetic depth sounding in the post-eruption phase of the Barren Island volcano
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