A seismic displacement brings us the useful information to analyze the seismic damage of infrastructure and buildings. In particular, a near-fault seismic ground motion including the huge residual displacement may cause the large response of tall buildings and base isolated buildings.
The residual displacement due to the earthquake is obtained from geodetic observations such as GNSS, while the time series of the displacement including the residual component can be estimated using the strong ground motion record. Generally, residual displacements obtained by geodetic observations are more accurate. However, residual displacements estimated from strong ground motion records can be used to investigate the distribution of the displacement since the strong ground motion observation network is denser than GNSS network in Japan.
The seismic acceleration record observed by a servo-seismometer is often contaminated by the baseline change due to the tilt motion of the apparatus, the effect of the electric hysteresis, and so on. For this reason, it is difficult to obtain the time series of the displacement including the residual component from the record. In such case, it is necessary to correct the baseline change of the accelerogram.
In this study, a new calculation technique is proposed to estimate the seismic displacement from the strong motion acceleration record. In the method, the time series of the displacement including the residual component is obtained by eliminating the step function component from the acceleration record in the frequency domain. The parameters of the step function component are determined to reduce the fluctuation of the displacement of coda part.
Applying the method to some acceleration records of the main shock of the 2016 Kumamoto Earthquake, the displacements are estimated more accurate than those estimated by existing method. In addition, the orbit of the particle motion can be drawn using the displacement estimated by the method. According to the result, it is revealed that the ground at Nishihara station went down about 150 cm and then consequently moved to east about 200 cm. Furthermore, the distribution of the residual displacement of the main shock of the 2016 Kumamoto Earthquake estimated by proposed method almost agrees with that obtained by GNSS observation.
