Schlömer, Antje, Geissler, Wolfram H., Jokat, Wilfried and Jegen, Marion (2017) Seismicity in the vicinity of the Tristan da Cunha hotspot: Particular plate tectonics and mantle plume presence. Journal of Geophysical Research: Solid Earth, 122 (12). pp. 10427-10439. DOI 10.1002/2017JB015017.

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Abstract

Earthquake locations along the southern Mid-Atlantic Ridge have large uncertainties due to
the sparse distribution of permanent seismological stations in and around the South Atlantic
Ocean. Most of the earthquakes are associated with plate tectonic processes related to the
formation of new oceanic lithosphere, as they are located close to the ridge axis or in the
immediate vicinity of transform faults. A local seismological network of ocean-bottom
seismometers and land stations on and around the archipelago of Tristan da Cunha, allowed
for the first time a local earthquake survey for one year. We relate intra-plate seismicity
within the African oceanic plate segment north of the island partly to extensional stresses
induced by a bordering large transform fault and to the existence of the Tristan mantle plume.
The temporal propagation of earthquakes within the segment reflects the prevailing stress
field. The strong extensional stresses in addition with the plume weaken the lithosphere and
might hint at an incipient ridge jump. An apparently aseismic zone coincides with the
proposed location of the Tristan conduit in the upper mantle southwest of the islands. The
margins of this zone describe the transition between the ductile and the surrounding brittle
regime. Moreover, we observe seismicity close to the islands of Tristan da Cunha and nearby
seamounts, which we relate to ongoing tectono-magmatic activity.

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