New investigations of an ultra-slow continental rifting revealed from hydroacoustic monitoring in the Bransfield Strait, Antarctica
From November 2005 to November 2006, we have operated an Autonomous Underwater Hydrophone (AUH) array in the Bransfield Strait and the Drake Passage, Antarctica. The array takes advantage of the efficient propagation of sound in the oceans to detect, locate and analyze the temporal and spatial distribution of small- to moderate-size earthquakes along the South Shetland Islands, Bransfield Strait and Scotia Sea. During the mooring period, a total of 1,294 earthquakes occurred in the Bransfield back-arc basin, while 2,514 total earthquakes were located from throughout the region including the South Shetland Trench and the Drake Passage. Earthquakes in the Bransfield concentrated in five main swarms, four of which occurred in August 2006. Two swarms at Edifice A near Deception Island and the Three-Sisters show a temporal propagation of seismicity (1~2 km/hr) that may be caused by magmatic activity. The other three swarms at Hook Ridge and the northeast rift zones show no propagation and may represent tectonic rifting without a magmatic component. This is consistent with a transition from volcanic to fault driven rifting from the SW to NE within the Bransfield. During August 2006, the entire length of the Bransfield back-arc was seismically active. In addition to Bransfield seismicity, the hydrophone array detected dozens of earthquakes from the South Shetland Trench and an intense swarm of earthquakes at an unidentified mid-plate location in the Drake Passage. Given the extinction of the Phoenix-Antarctic Ridge (Lawver et al., 1996), seismicity in the trench and back-arc is likely a result of slab rollback. Earthquake swarms, combined with the ~10 mm/yr spreading rate from GPS measurement (Dietrich et al., 2001), demonstrate that the Bransfield Strait is in an ultra-slow continental rifting regime.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 3000 MARINE GEOLOGY AND GEOPHYSICS;
- 3001 Back-arc basin processes;
- 3075 Submarine tectonics and volcanism