Cruise Summary Report POS480,05th Feb. – 12th Feb., 2015, Las Palmas – Las Palmas (Spain)

Abstract

The ongoing unrest of el Hierro Islands started in 2011 with a submarine volcanic eruption 2 km South of El Hierro and poses a significant hazard potential for the island and its inhabitants. The spatial distribution of seismicity is highly variable and a significant part of is occurs outside the network or offshore. In order to better characterize the seismicity the seismological network was densied with 8 ocean bottom seismometers (OBS) during Poseidon cruise POS480. The permanent network of IGN was densified with 9 onshore stations in March 2015. Beside a better depth estimate of the seismicity OBS data will allow a better characterization of the seismic signals due to an improved spatial coverage of the Island and its surrounding. The offshore supplement of the network will enable a much more improved hypocentral estimate, which in turn will allow to resolve the structures involved in the current seismic unrest as well as its spatial temporal characterization. OBS stations will be deinstalled early 2016. Swath bathymetry mapping of the 2011 eruption site was planned to reveal bathymetriy changes related to the growth of the new volcanic cone offshore the southern tip of ElHierro's coast. Additionally, we planned to use the multibeam system to monitor for upwelling gas flares in the water column. During the cruise 8 OBS stations were installed. The stations are equipped with lithium batteries which allow to register local seismicity for a period of 12 months. The deinstallation of the OBS is planned for log1 of Poseidon cruise POS 494 (04 February 2016 until 08 February 2016). Following the diplomatic clearance no multibeam data was measured.