Microearthquake seismicity of the Mid-Atlantic Ridge at 5°S: A view of tectonic extension

Research output: Contribution to journalArticlepeer-review


  • Frederik Tilmann
  • Ernst Flueh
  • Lars Planert
  • Tim Reston
  • Wilhelm Weinrebe

Colleges, School and Institutes

External organisations

  • Boston University
  • University of Cambridge
  • GEOMAR - Helmholtz Zentrum für Ozeanforschung Kiel
  • Bullard Laboratories
  • Leibniz-Inst F Meereswissenschaften
  • Universität Kiel (IFM-GEOMAR)
  • Leibniz Inst Meereswissensch


We report measurements made with an ocean bottom array which was operated for 10 days on the Mid-Atlantic Ridge just south of the 5°S transform fault/fracture zone. A total of 148 locatable earthquakes with magnitudes ∼0.5-2.8 were recorded; seismic activity appears to be concentrated within the western half of the median valley. The median valley seismic zone is bounded in along-axis direction by the transform fault to the north and the tip of the axial volcanic ridge to the south. A few scattered events occurred within the inside corner high, on the transform fault, and in the western sidewall close to the segment center. Earthquakes reach a maximum depth of 8 km below the median valley floor and appear to be predominantly in the mantle, although a few crustal earthquakes also occurred. The presence of earthquakes in the mantle indicates that it is not strongly serpentinized. We infer the median valley seismic activity to primarily arise from normal faulting.


Original languageEnglish
JournalJournal of Geophysical Research
Issue number6
Publication statusPublished - 10 Jun 2004