Spatiotemporal evolution of ground motion and direct test of the ATL law

Long-term variations in the spatial displacement of the tunnel floor at the KEKB injector linac have been analyzed based on spatiotemporal evolution of ground motion measured with a remote-controllable sensing system. The amount of the displacement data has been recorded at a fixed interval since January 2016 in order to directly validate random walk characteristics of the tunnel-floor displacement due to the complex ground motion. The ATL law is well known as an experimental rule in geophysics field, which describes stochastic spatiotemporal evolution of ground motion. Based on the stochastic spatiotemporal evolution of ground motion, displacement level of the tunnel floor may only increase without any periodicity nor reduction. If the spatiotemporal evolution of the displacement level is too large, we may have to discuss again about the high precision alignment required for the injector linac. In this report, based on the long-term dynamic variations in the spatiotemporal displacement of the tunnel floor measured at the injector linac, the spatiotemporal evolution of ground motion is investigated to test directly the ATL law, and the magnitude of the parameter in the ATL law is quantitatively evaluated. (author)