Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain)

We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geografico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10-12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low-and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.