Baseline correction of ground motions with physics-based correction patterns

Recovery of ground displacements from strong motion accelerographs alone is still performed in an empirical way. This paper starts with a theoretical description of strong motion instruments. Then, based on observations from the non-tilt 2-D shake table tests, this paper proposes a baseline correction procedure with a cumulative correction pattern. The procedure is validated by recorded displacements of the shake tables. The paper also extends the baseline correction procedure to deal with 3-D strong motions by introducing a tilt correction pattern. The results from the proposed baseline correction procedure are compared with those from an existing empirical baseline correction procedure as well as nearby GPS measurements. The accuracy of the proposed procedure is studied considering 41 accelerographs and the corresponding GPS stations that recorded the 2011 Mw 9.0 Tohoku earthquake in Japan. We find that the corrected displacements from recorded accelerations alone are not always consistent with the GPS measurements. In this specific Tohoku event of which the primary direction of motion was eastward, the ground displacements derived from strong motion stations using the proposed baseline correction procedure achieve the best agreement in the east–west direction. Meanwhile, the proposed procedure is computationally efficient.