Fig. 3

Temporal variation of attitudes and temperature of the recording packages. Upper: roll, pitch and heading angles are plotted with time for two recording units. OBXA (the southern station) and OBXC are estimated for installation on the seafloor covered with sand and rocks, respectively. Angles are generally stable during the observation, although the attitude of OBXA largely changed on June 5, 2019. It is possible that the recording package was pulled. Lower: temporal changes of temperature for both units are also small, except for June 6th for OBXC. A small variation in temperature of the unit lowers the error of the timing, which is based on a crystal oscillator in the unit