Fig. 4

Characteristics of the steps a Raw and reduced tilt variation and occurrence frequency of steps in 10 days; b An example of a step in a time series; and c cumulative amount of steps in the horizontal plane. In the top two panels in (a), gray and black lines show the raw tilt variation and tilt variation after reduction of the step. In (a) and (b), X and Y components indicate each component of the sensor of the pendulum tiltmeter. In (c), the color of each data point indicates the elapsed time since installation