Presenter: Lauren Schmahl (Queens College - CUNY)

Description:
The Bransfield Strait is a seismically active back-arc basin located between the Antarctic Peninsula and the South Shetland Islands.  Although subduction in the region slowed around four million years ago, back-arc volcanism and extension have continued through the basin and the back-arc rift may be nearing the transition to seafloor spreading. BRAVOSEIS (BRAnsfield VOlcano SEISmology) is an international effort that collected a multifaceted geophysical data set focused on the understanding of the submarine volcanoes and the complex tectonic regime in the Bransfield Strait. During the 2019 expedition, six NOAA hydrophones were placed throughout the Bransfield Strait and were retrieved during the 2020 expedition. The data collected from each hydrophone was analyzed using IDL software to identify the arrival time, frequency content for each underwater acoustic event. Locations are calculated using a grid search that uses an iterative nonlinear regression algorithm to minimize error from observed and predicted travel times of potential locations. Ongoing analysis of the data has identified over 3000 acoustic events from about one third of the data set. There are over 1000 ice-quakes, many high-quality sequences of fin whale vocalizations, and over 300 earthquake events. Many of the earthquakes are located along the rift and centered near Orca Volcano. The acoustic magnitude of the earthquakes ranges from 170 to 225 dB,  which relates to seismic magnitude that ranges from 3- 5 mb.  This data set complements seismic data collected on a regional network of seismometers over the same period and future work will include comparing the hydroacoustic and seismic earthquake catalogues.