Baseline correction for digital strong-motion records by using the pre-event portion

:Baseline offset in digital strong-motion acceleration record and initial velocity can produce unrealistic results for ground velocity and displacement derived from the acceleration by integration. A new method is proposed for the baseline correction and initial velocity calculation. It is based on linear least-squares fitting of the pre-event portion of velocity derived from the uncorrected acceleration data. Compared with the conventional method, which is based on removing the mean values of the pre-event portions of the acceleration and velocity traces, this method has clearer physical meaning and better stability.