February Geology and GSA Today media highlights

Boulder, CO - Topics include: a new technique for analyzing the relationship between climate and hurricane activity; discovery of fossilized embryos in advanced stages of development from South China; revised dispersal and extinction dating of the late Neogene "terror bird"; new data illustrating real-time changes beneath a large Antarctic glacier; evidence that mid-latitude North America's prevailing winds once blew from east to west; and recent formation of a mud volcano in an area of active petroleum exploration.

Active deformation across the Sumatran forearc over the December 2004 MW 9.2 rupture
Donald Fisher, Pennsylvania State University, Department of Geosciences, University Park, PA 16802, USA; et al. Pages 99-102.

The Sumatra earthquake and tsunami offshore survey (SEATOS) expedition off the coast of Sumatra collected seismic reflection data that provide an image of the shallow structures in the area of greatest slip during the December 2004 MW 9.2 rupture of the Sunda plate boundary. This image depicts folding of the sediment layers that once blanketed the upper plate, with continued infilling of isolated slope basins and evidence for ongoing shortening across the entire region. The shortening of this sediment blanket, combined with the structure of the deformation front, indicates that plate boundary slip, such as the 2004 event, likely occurs as the strong inner wedge surges forward and peels up the shallow portion of the sediment fill. Each event produces one shortening increment in the sedimentary blanket across the upper plate, with folds representing the accumulated shortening of many earthquakes. This permanent shortening thickens the sediments of the upper slope and, with the elastic rebound of the inner wedge, could contribute to the generation of tsunamis.

Bedrock channel adjustment to tectonic forcing: Implications for predicting river incision rates.
Alexander C. Whittaker, University of Edinburgh, School of Geosciences, Grant Institute, Edinburgh, Scotland EH9 3JW, UK; et al. Pages 103-106.