HR: 1340h
AN: S43A-1065    [Abstracts]
TI: The Ground Tilt in the 1999 Chi-Chi, Taiwan Earthquake
AU: * Chiu, H
EM: chiu@earth.sinica.edu.tw
AF: Institute Of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei, 11529, Taiwan
AB: The baseline of a strong-motion record is very sensitive to the leveling change of the accelerometer. A tilting angle x (in radian) will cause a baseline drift about 980 sin(x) cm/s/s in the horizontal component and about 980(1- cos(x)) cm/s/s. in the vertical component. The effect of this baseline drift can be further magnified in a displacement waveform. Although the tilting is not the only source of baseline drifts, the baseline drift due to the tilting can be easily identified and separated from other types of baseline drifts because the tilting always appears in middle of a record and happens during or after the large shaking. The length of the surface rupture in the 1999 Chi-Chi Taiwan earthquake is about 80km with large ground motions; the maximum recorded ground velocity is over 3m/s, and the maximum ground displacement is over 10m. Some recordings near the surface rupture show significant baseline drift due to the ground tilt. In this study, we measure the ground tilt due to the Chi-Chi earthquake at 167 strong-motion stations. Among them, several stations are only few tens meters away from the surface rupture. As expected, the baseline drift of vertical component is smaller than that of the horizontal component. In general, the ground tilt is small no matter the fact that the permanent displacements are large at hanging-wall stations; the maximum tilting angel is about 0.5 degree while the most stations are less than 0.02 degree.
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting