The Taipei basin is a triangle-shaped formation. The ground surface of the
basin is almost flat, but tilting gently to the northwest. The geological s
tructure inside the basin consists of Quaternary layers above the Tertiary
base rock. A dense strong motion observation network has operated in the Ta
ipei area since 1991, as part of the Taiwan Strong Motion Instrumentation P
rogram (TSMIP), Characteristics of site effects in the Taipei basin are stu
died using the data recorded by this observation network. In this study, th
e method of amplitude spectrum ratio is used to analyze site effects in the
Taipei basin, This analysis clearly shows that the spectral ratio contours
at low frequency bands (0.2 - 1 Hz) correlate with the structures of the T
ertiary basement shape and the top soft soil layer. For the higher frequenc
y band (1 - 3 Hz), the main amplification effects occur near the north, eas
t, and south basin edges. This shows that the edge effect found in the Kobe
earthquake could possibly occur in this area. Dominant frequencies in the
Taipei basin area are also given in this study. This will benefit the micro
zonation work for future earthquake hazard mitigation in the Taipei basin.