USAP-DC

One of the fundamental processes in plate tectonics is the rifting or separating of continental crust creating new seafloors which can widen and ultimately form new ocean basins, the latter is a process known as seafloor spreading. The Bransfield Strait, separating the West Antarctic Peninsula from the South Shetland Islands, formed and is presently widening as a result of the separation of continental crust. What is unique is that the system appears to be approaching the transition to seafloor spreading making this an ideal site to study the transitional process. Previous seafloor mapping and field surveys provide the regional structure of the basin; however, there exists a paucity of regional seismic studies documenting the tectonic and volcanic activity in the basin as a result of the rifting. This would be the first local-scale study of the seismicity and structure of the volcanoes in the center of the basin where crustal separation is most active. The new seismic data will enable scientists to compare current patterns of crustal separation and volcanism at the Bransfield Strait to other well-studied seafloor spreading centers. This collaborative international project, led by the Spanish and involving scientists from the U.S., Germany and other European countries, will monitor seismicity for one year on land and on the seafloor. An active seismic study conducted by the Spanish will image fault and volcanic structures that can be related to the distribution of earthquakes. Back-arc basins are found in subduction settings and form in two stages, an initial interval of continental rifting that transitions to a later stage of seafloor spreading. Studying the transitional process is important for understanding the dynamics and evolution of subduction zones, and in locations where back-arc rifting breaks continental crust, it is relevant to understanding the formation of passive continental margins. The Central Bransfield Basin is unusual in that the South Shetland Islands have lacked recent arc volcanism and it appears subduction is ceasing, but this system has broad significant because it appears to be nearing the transition from rifting to seafloor spreading. This award will support the U.S. component of an international initiative led by the Spanish Polar Committee to conduct a study of the seismicity and volcanic structure of the Central Bransfield Basin. The objective is to characterize the distribution of active extension across the basin and determine whether the volcanic structure and deformation of the rift are consistent with a back-arc basin that is transitioning from rifting to seafloor spreading. The U.S. component of the experiment will contribute a network of six hydroacoustic moorings to monitor regional seismicity and 15 short-period seismometers to study the distribution of tectonic and volcanic seismicity on Orca volcano, one of the most active volcanoes in the basin. An active seismic study across closely spaced multichannel seismic lines across the rift will provide the data necessary to link earthquakes with fault structures enabling a tomography study of Orca volcano and provide insight into how the volcano's structure relates to rifting. This research will constrain the distribution of active rifting across the Central Bransfield Basin and determine whether the patterns of faulting and the structure of volcanic portion of the rift are consistent with a diffuse zone of rifting or a single spreading center that is transitioning to the production of oceanic crust. The Bransfield Basin is an ideal site for a comparative study of seismic and hydroacoustic earthquake locations that will improve the understanding of the generation and propagation of T-wave signals and contribute to efforts to compare the result of T-wave studies with data from traditional solid-earth seismic studies. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Person	Role
William, Wilcock	Investigator and contact
Dax, Soule	Co-Investigator
Robert, Dziak	Co-Investigator

Antarctic Earth Sciences

Award # 1744651

USAP-1744651_1

Deployment	Type
BIO Hespérides (A-33)	ship expedition
BO Sarmiento de Gamboa	ship expedition

None in the Database

Repository	Title (link)	Format(s)	Status
NSF SAGE Facility DMC	Bransfield OBSIC OBS network 2019-20 (network code ZX, 2019)	Not Provided	exists
GEOFON	BRAVOSEIS Onshore Seismic Array (Network code 5M)	Not Provided	exists
Marine Geoscience Data System	3D P-wave velocity models of Orca Volcano, Bransfield Basin, Antarctica from the BRAVOSEIS experiment	Not Provided	exists

1. Almendros, J., Wilcock, W., Soule, D., Teixidó, T., Vizcaíno, L., Ardanaz, O., ... & Schmahl, L. (2020). BRAVOSEIS: Geophysical investigation of rifting and volcanism in the Bransfield strait, Antarctica. Journal of South American Earth Sciences, 104, 102834. (doi:10.1016/j.jsames.2020.102834)
2. Kidiwela, M., W. S. D. Wilcock, D. C. Soule, J. Almendros,. Late-Stage Rift Evolution at Back Arc Basins: Insights from a Tomography Experiment at Orca Volcano, Bransfield Basin. ESS Open Archive . February 12, 2025. (doi:10.22541/essoar.173939638.88887432/v1)