The solid Earth is covered by tectonic plates, and the tectonic deformation is active at the interfaces between them. Most of huge earthquakes as large as magnitude 8–9 occurred along the plate boundary, especially along the subduction zones that frequently form large trenches and troughs. To monitor the crustal deformation in such regions is important to mitigate the earthquake hazards. Because almost all the subduction zones are covered by ocean, where the GNSS’s electromagnetic wave cannot reach, acoustic technique plays essential role. The Japan Coast Guard has been developing and operating the GNSS-A observation, that is a combination technique of GNSS and underwater acoustic, to locate the seafloor position at the precision of centimeters. We use the survey vessels whose position is precisely determined by GNSS to measure the acoustic travel time between the onboard transducer and the pre-installed seafloor transponders. For acoustic ranging, we use bi-phase modulated signal with the ninth order M-sequence code (four waves for one bit) at a carrier wave frequency of 10 kHz (the length of signal is 204.4 ms). acoustic signal. In this presentation, we introduce the overview and current updates in our GNSS-A observation technique, focusing on the importance for the earthquake monitoring.
Watanabe et al. (Wed,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: