Abstract: On June 1, 1996, an earthquake (MS = 5. 4) occurred in Tianzhu-Gulang region, Gansu Province. In this paper, the short period digital seismic data at CDSN Lanzhou station was processed by Seismgram software, which is recommend by IASPEI. The wave spectra of three foreshocks and fourteen after-shocks of Tianzhu-Gulang MS 5. 4 earthquake w ere studied. The results are shown as follows: ① The logarithm ratio value of level of zero sequence of displacement spectrum reduced from 1. 2 before mainshock to 1. 0 after main shock. ② The corner frequency ratio value and the high sequence spectrum of oblique factor ratio value reduced from 1. 0 before mainshock to 0. 8 after mainshock. ③ The every characteristic curve of wave spectrum shows same form in the same anomaly period. ④ There are remarkable anomaly characteristics before and after the mainshock. So it may become an important index for earthquake prediction.

Key words: Seismic wave spectrum, Spectral analysis, After-shock, Tianzhu-Gulang earthquake