Cenozoic tectonic history, seismicity and palaeoseismicity of the Antarctic Peninsula Pacific margin

Global earthquake catalogues do not record any earthquakes south of Bransfield Strait beneath the Antarctic Peninsula or its flanking continental shelves. Such low seismicity is consistent with neotectonic interpretations which show the area south of Bransfield Strait as part of the modern Antarctic plate. However, the magnitude distribution of earthquakes located in the wider region indicates that the threshold for location of events in this area was at least mb=4.5 before 1996. Plate tectonic reconstructions indicate that rapid subduction was taking place along the entire Pacific margin of the Antarctic Peninsula at the start of the Cenozoic era. By analogy with active subduction zones, and by reference to statistical relationships between seismicity parameters and other measurable parameters of modern subduction zones, it is inferred that this was an area of intense seismic activity at that time. On the same basis, wellconstrained tectonic events affecting this margin imply that seismic activity decreased in stages during the Cenozoic era. Global catalogues list four earthquakes beneath the continental rise west of the Antarctic Peninsula. These occurred in oceanic lithosphere 16–49 Ma in age and do not appear to be associated with oceanic fracture zones. Harvard CMT focal mechanisms for two of these

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