ALBERT

Description: The seafloor stores crucial information on sub-seafloor processes, including stress, elastic strain, and earthquakes. This information may be extracted through the nascent scientific field of seafloor geodesy. The GeoSEA (Geodetic Earthquake Observatory on the SEAfloor) array uses acoustic signals for direct-path ranging and relative positioning at mm-scale resolution for a period of up to 3.5 years. The transponders also include high-precision pressure sensors to monitor vertical movements and dual-axis inclinometers in order to measure their altitude as well as subsidence or uplift of submarine fault zones. A further component of the network is GeoSURF, a self-steering autonomous surface vehicle (Wave Glider), which monitors system health and is able to download the seafloor geodetic data to the sea surface and to transfer it via satellite. At present, the geodetic seafloor transponders are monitoring: The southern dextral strike-slip fault of the eastern flank of Mt Etna in Sicily, where a recent slow slip event indicates the instability of the offshore volcanic flank. The North Anatolian Fault in the Sea of Marmara offshore Istanbul to measure the strain build-up along the Main Marmara fault. The North Chilean subduction zone system, where three transponder arrays are deployed on the marine forearc and outer rise. This segment of the Nazca-South American plate boundary has last ruptured in an earthquake in 1877 and was identified as a seismic gap prior to the 2014 Iquique earthquake (Mw 8.1). The southern portion of the segment remains unbroken by a recent earthquake. The first 12 month of all geodetic installations were analyzed and we discuss baselines and baseline changes with precision less 5 mm for ranges up to 2000 m of distance.