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Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio (SNR), which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.

39473 Pn travel times are inverted to tomographically image both lateral variation and anisotropy of uppermost mantle velocities beneath China continent. The result indicates that the overall average Pn velocity of uppermost mantle in the studied region is 8.0 km/s and the regional velocity fluctuation varies from -0.30 km/s to +0.35 km/s. Pn velocities higher than 8.2 km/s are found in the regions surrounding Qingzang Plateau, such as Junggar Basin, Tarim Basin, Qaidam Basin and Sichun Basin. Pn velocities slightly lower than the average are found in western Sichuan and Yunnan, Shanxi Graben and Bohai Bay region. A Pn velocity as low as 7.8 km/s may exist in the region striding the boundary between Guangxi and Guangdong provinces. In general, Pn velocity in tectonically stable region like cratonic platform tends to be high, while that in tectonically active region tends to be low. The regions in compressive setting usually show higher Pn velocity, while extensional basins or grabens generally display lower one. Anisotropy of Pn velocity is seen in some regions. In the southeastern region of Qingzang Plateau the directions of fastest Pn velocity show a rotation pattern, which may be related to southeastward escape of the plateau material due to the collision and compression of Indian Plate to Asia along Himalaya arc. Notable anisotropy also exists around Bohai Bay region, likely indicating crustal extending and possible magma activity therein.