Recently, Uchida et al. [2016, Science] revealed the periodic changes in the interplate locking in the northeast Japan subduction zone based on the activity of small repeating earthquakes and terrestrial crustal deformation data. They found that slow slip on the plate interface has occurred repeatedly at intervals of from 2 to 6 years, depending on the location. In the northern part of the Japan Trench, a tsunami earthquake occurred with rupturing the shallow plate boundary in 1896, but it is not well understood whether the coseismic slip fully released the interseismic slip deficit, and whether periodic slow slip events occur near the trench or not. In order to investigate the interplate locking state in this region, we have just started a research project titled “Head and tail of massive earthquakes: Mechanism arresting growth of interplate earthquakes” (JSPS KAKENHI Grant Number JP19H05596), under which GNSS-Acoustic observation to detect the seafloor crustal deformation will be performed more frequently than ever before. To accomplish frequent observations, we have been developing automatic GNSS-A data acquisition system using an unmanned surface vehicle, the Wave Glider. As a first observation, we have performed GNSS-A observation at a seafloor station off Aomori Prefecture in this July. The Wave Glider (SV3-240) was equipped with 2 GNSS antennas, acoustic transducer, MEMS gyro, and their control and logging units. The data acquisition from these sensors and the autonomous activation of the seafloor transponders were successfully executed only with turning the power supply to the payload on/off from land via a satellite communication. The Wave Glider rarely strayed off the configured course, and the solar panels generated enough power to perform the observations although the weather was mostly cloudy during the operation. Now, we are processing the obtained data, and the results will be presented at the meeting.