Relative motions between cross-fault sites resultd from the 1999 M_W7.6 Taiwan Chi-Chi earthquake

In order to obtain more accurate residual displacement information generated by near-fault ground motion, this paper proposed a variable step-grid search method for ground motion baseline correction. The core of this method lies in preserving and accurately reflecting the residual displacement information of faults, and solving the problem of extremely low computational efficiency in traditional grid search methods when there are many digital seismic sampling points. Based on the strong ground motion data of the 1999 M_W7.6 Chi-Chi earthquake in Taiwan region, this paper uses the variable step-grid search method for ground motion baseline correction to conduct in-depth research on the ground motion displacement characteristics near faults. By accurately correcting the initial moment of ground motion time history, this study successfully obtained relative ground motion time history data between multiple sets of the hanging and foot wall stations in the Chi-Chi earthquake. And based on this data, the displacement time history characteristics of the relative motion between the hanging and foot wall sites near the fault were analyzed. The research results indicate that the fling-step effect of ground motion is particularly significant in the Chi-Chi earthquake. The maximum displacement and residual displacement of near fault ground motion exceed 8 m and 6 m, respectively, and the average sliding velocity of the fault is as high as 1.4 m/s, fully demonstrating the strong destructive force of the earthquake. This poses challenges to the numerical simulation of fault rupture and related experimental researches. In addition, the relative motion between fault walls also exhibits similar motion characteristics to near fault ground motion, and its amplitude is larger. Therefore, the relative motion data between earthquake fault walls can refer to the time history of near fault ground motion as the input basis for engineering design and analysis. In addition, the residual displacement of the fault is about 80% of the maximum relative displacement between the fault walls. This study provides important information on residual displacement of fault ground motion, which is of great significance to the researches on fields such as earthquake engineering, earthquake warning, and disaster assessment.