An Automatic Scheme for Baseline Correction of Strong-Motion Records in Coseismic Deformation Determination

Coseismic deformation can be determined from strong-motion records of large earthquakes. Iwan et al. (1985) showed that baseline corrections are often required to obtain reliable coseismic deformation because baseline offsets lead to unrealistic permanent displacements. Boore (2001) demonstrated that different choices of time points for baseline correction can yield realistically-looking displacements, but with variable amplitudes. The baseline correction procedures of Wu and Wu (2007) improved upon Iwan et al. (1985) and achieved stable results. However, their time points for baseline correction were chosen by a recursive process with an artificial criterion. In this study, we follow the procedure of Wu and Wu (2007) but use the ratio of energy distribution in acceleragrams as the criterion to determine the time points of baseline correction automatically. This avoids the artificial selection of time points and speeds up the estimation of coseismic deformations. We use the 2003 Chengkung and 2006 Taitung earthquakes in eastern Taiwan to demonstrate this new approach. Comparison between the results from this and previous studies shows that our new procedure is suitable for quick and reliable determination of coseismic deformation from strong motion records.