Parallel bands of seismicity at the Mid-Atlantic Ridge, 12-14°N

Abstract

Seismicity distribution along the Mid-Atlantic Ridge (MAR), monitored with the Autonomous Underwater Hydrophone (AUH) array, shows a band of seismicity ∼70 km west of the axis between ∼11.9°N and 14.2°N. Available focal mechanisms at the off-axis seismic band show extension directions consistent with the accommodation of the North-American (NA) and South-American (SA) relative plate motion. Axial seismicity shows a gap at ∼14°N, coinciding with the 14°N hotspot-like region, and the focal mechanisms near this region are consistent with spreading of the African (AF) and the NA or SA plates. We speculate that the triple junction between the AF, NA and SA plates is close to the 14°N seismic gap. The westward continuation of the NA-SA plate boundary is unconstrained, but could initiate at ∼13°N, at the south end of the off-axis seismic band, or be diffuse between ∼12°N and ∼15°N.