ALBERT

Description: Within Europe there are more than 380 Ocean Bottom Seismometers (OBS) distributed across 10 instrument parks in 6 countries. At least 120 of these OBS are wideband or broadband, over 260 can be deployed for at least 6 months at a time and 140 for at least one year. New parks are planned in two other European countries, which should add over 70 OBSs to this “fleet”. However, these parks are under the control of individual countries or universities and hence to date this has made it difficult to organize large-scale experiments, especially for seismologists without marine experience. There has recently been an initiative to coordinate the use of these distributed instruments and their data products, to encourage large-scale experiments, possibly with onshore and offshore components, by seismologists who have not necessarily used OBSs before. The ongoing or planned developments include: Helping scientists with marine-specific formalities such as ship requests; clearer explanations of the noise floors of OBS instrumentation; improved clarity of instrument pricing and availability; standardized data output formats and data validation; and archiving in established seismological data centers. These efforts should allow improved experiment design in scientifically interesting regions with an offshore component and an easier, clearer way to organize large-scale, multi-country experiments. We will present details of this initiative to help organize large-scale experiments, the particularities of OBS sensors and marine deployments, the available instrumentation and new developments.

Description: Laser reflectometry (BOTDR), commonly used for structural health monitoring (bridges, dams, etc.), will for the first time be applied to study movements of an active fault on the seafloor 25 km offshore Catania Sicily. The goal of the European funded FOCUS project (ERC Advanced Grant) is to connect a 6-km long strain cable to the EMSO seafloor observatory in 2100 m water depth. Laser observations will be calibrated by seafloor geodetic instruments and seismological stations. A long-term goal is the development of dual-use telecom cables with industry partners.

Description: The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. To univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys ocean and to confute its interpretation as a strongly thinned part of the African continental crust, a NE-SW oriented 131 km long seismic refraction and wide-angle reflection profile consisting of eight ocean bottom seismometers and hydrophones was acquired in 2014. A P-wave velocity model developed from travel time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6km thick crust with velocities ranging from 5.1km/s to 7.2km/s, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina Seamounts at the southern IAP boundary, the crust thickens to about 9km and seismic velocities decrease to 6.8km/s at the crust-mantle boundary. The seismic velocity distribution and depth of the crust-mantle boundary in the IAP document its oceanic nature, and support the interpretation of the IAP as a remnant of the Tethys oceanic lithosphere formed during the Permian and Triassic period.