The first fully monitored volcanic eruption in the Canary Islands started on 10 October 2011, 2 km south of the island of El Hierro. This submarine eruption was preceded by various precursory signals, the most evident of which were the seismic series that started in July 2011 consisting of almost 10,000 low‐magnitude earthquakes located by manual picking. This seismicity revealed a 20 km horizontal migration from the north of the island to the south at depths of between 10 and 17 km, the deeper events occurring further south. We applied a relative location algorithm (hypoDD) to improve hypocentral locations. The resulting distribution is more compact, slightly shallower, and reveals a clearer difference in depths from north to south. Tests performed to check the reliability of the results gave maximum uncertainties of 400 m in the relocations. Furthermore, new features were found, including the origin of the seismicity in the center of the island and the presence of two alternating seismogenic zones in the north of the island during the first month of activity.
Online Material: Figures of waveforms from cross correlation, data statistics, stereogram of ray parameters, ray‐tracing tests, and table of hypoDD relocations.