On the relation between ground surface deformation and seismicity during the 2012–2014 successive magmatic intrusions at El Hierro Island

Abstract

Six different magmatic intrusions were detected around El Hierro Island in the two years that followed the end of the 2011–2012 submarine eruption. Each intrusion lasted between few days to three weeks and produced intense seismic swarms and rapid ground deformation. We performed a hypoDD relocation of >6000 earthquakes and inverted the GPS data in order to obtain the location of the magma source of each intrusion. Each episode presents a spatial gap between seismicity and magma source of 3–8 km with the earthquakes located always deeper than the deformation sources. We propose a magma plumbing system consisting on a deep structure injecting magma to a more ductile shallower location beneath El Hierro crust. While the seismicity is associated with the deeper structure, the ascent and accumulation of magma at shallower level deforms the crust aseismically. The mechanism of most of these episodes consists of an initial injection of magma producing most of the ground deformation and high b-values of the seismicity indicating fluid fractures during the first days and finishes with high magnitude earthquakes and low b-values indicating an overpressure of the injection process. There is a correlation between the seismic and geodetic moment ratio and the direction of propagation of each intrusion towards one of the volcanic rifts of the island, suggesting the possible existence of a deep structure beneath the island related with to the triaxial origin of the island. This work presents important advances in the knowledge of monogenetic magmatic intrusions and, specifically, in those occurred in El Hierro Island between 2011 and 2014, with important implications for future volcano monitoring in the Canary Islands.