Error evaluation in acoustic positioning of a single transponder for seafloor crustal deformation measurements

摘要

The observation of seafloor crustal deformation is very important to understand plate motions, nucleation processes and mechanisms of great interplate earthquakes as well as the activities of submarine volcanoes. We have been developing an observation system for seafloor crustal deformation. This system consists of two main components; (1) kinematic GPS positioning of an observation vessel and (2) accurate acoustic measurements of distances between a transponder attached on the side of the vessel (onboard station) and one located on the ocean bottom (seafloor station). In this study, we performed numerical simulations to estimate measurement errors with acoustic positioning assuming acoustic velocities in the sea water and the distribution of observation points around the single seafloor station. We found that the position of the seafloor station which we can obtain by analyzing travel-time data might have around 18-cm discrepancy with respect to its "true" position. Colombo et al. (2001) reported that the position of the vessel can be determined with about 10-cm error by kinematic GPS positioning. These results indicate that the system should be able to detect seafloor crustal deformation much larger than 28 cm, including pre-, co-, and post-seismic slips due to the large earthquakes at subduction zones, slow and silent earthquakes, etc. Therefore, we emphasize the importance of continuous observations with a nationwide geodetic observational network for seafloor crustal deformation