Crustal structure of Deception Island volcano from P wave seismic tomography: Tectonic and volcanic implications

Abstract

Deception Island (62°59′S, 60°41′W) is an active volcano located in the Bransfield Strait between the Antarctic Peninsula and the South Shetland Islands. The island is composed of rocks that date from <0.75 Ma to historical eruptions (1842, 1967, 1969, and 1970), and nowadays most of its activity is represented by vigorous hydrothermal circulation, slight resurgence of the inner bay floor, and intense seismicity, with frequent volcano‐tectonic and long‐period events. In January 2005 an extensive seismic survey took place in and around the island to collect high‐quality data for a high‐resolution P wave velocity tomography study. A total of 95 land and 14 ocean bottom seismometers were deployed, and more than 6600 air gun shots were fired. As a result of this experiment, more than 70,000 travel time data were used to obtain the velocity model, which resolves strong P wave velocity contrasts down to 5 km depth. The joint interpretation of the Vp distribution together with the results of geological, geochemical, and other geophysical (magnetic and gravimetric) measurements allows us to map and interpret several volcanic features of the island and surroundings. The most striking feature is the low P wave velocity beneath the caldera floor which represents the seismic image of an extensive region of magma beneath a sediment‐filled basin. Another low‐velocity zone to the east of Deception Island corresponds to seafloor sedimentary deposits, while high velocities to the northwest are interpreted as the crystalline basement of the South Shetland Islands platform. In general, in the tomographic image we observe NE‐SW and NW‐SE distributions of velocity contrasts that are compatible with the regional tectonic directions and suggest that the volcanic evolution of Deception Island is strongly conditioned by the Bransfield Basin geodynamics.