Seafloor geodesy to monitor deformation offshore Northern Chile (GeoSEA)

Within the last decade, satellite-based geodetic techniques such as GPS or InSAR have increased our knowledge about tectonic plate motions and crustal deformation. However, the electromagnetic waves used by these techniques do not penetrate into water and therefore geodetic information for the offshore domain is sparse. The GeoSEA (Geodetic Earthquake Observatory on the SEAfloor) array uses acoustic ranging techniques between stations on the seafloor for relative positioning. We use data from 23 autonomous acoustic transponders installed in three deployments located on the outer rise and on the marine forearc of the northern Chile subduction zone (~21°S). The networks are located immediately south of the Iquique 2014 Mw 8.1 rupture zone. Stations were deployed in December 2015 and were mostly recording until June 2018. The geodetic networks monitor crustal deformation of the seafloor with the target to quantify interseismic deformation. Although we achieve a mm-scale precision with our acoustic ranging system, we observe no significant deformation above our resolution limits. We compare our observations with surface strain models estimated using onshore cGPS stations of the Plate Boundary Observatory Chile (IPOC). The predicted strains are of a similar order of magnitude compared to the strain resolution of the network. Furthermore, we show pressure data for all three networks. Although the resolution of the pressure sensors is in the cm-range, the data do not reveal any sudden vertical movements of the seafloor, indicating absence of vertical crustal movement.