The High‐Cut Parameter (Kappa) for the Near‐Surface Geology in and around the Taipei Basin, Taiwan

Abstract

Abstract The decay parameter at the high frequency (kappa value, κ ) introduced by Anderson and Hough (1984) is measured from 54 stations situated in and around the Taipei basin, northern Taiwan. Different frequency windows for the S ‐wave amplitude spectra are used to measure the κ r value for each individual record. The preferred κ r values are determined by the least‐squared fitting with the best correlation coefficient. The site‐specific κ 0 values, which are computed by removing the anelastic effect of regional geological structure by grouping κ r into the crustal and subduction events according to the focal depth and site classification (i.e., class B, C, D, and E sites), are calculated to be in the range of 0.034–0.066 s. We correlate the κ 0 values with the averaged shear‐wave velocity of the topmost 30‐m layer V S 30 and find the independence of κ 0 on V S 30 . In addition, 28 stations lie on sediment in the Taipei basin. The gradient of κ 0 versus the sedimentary thickness to the Tertiary base in the basin is calculated, and then used to estimate the effective quality factor Q ef of the layer. Q ef is 75.3 for the whole sedimentary layers (above the Tertiary base). Given one standard deviation, Q ef are in the 41.9–376.7 range. Q ef can provide an accurate referred parameter for the future ground‐motion simulation applications.