Characteristic period of response spectrum for surface and borehole ground motions

Determining the characteristic period of ground motions (Tg) is an essential step in the seismic design of structures, but a critical problem that needs to be solved is figuring out how to do so when bedrock ground motion is utilized as an input. In this paper, the relationship between surface and borehole temperature data is investigated, and the main factors affecting the Tg are analyzed. Then, the algorithm for predicting Tg is presented. It is found that two factors, i.e., peak ground acceleration (PGA) and fault distance have significant effects on the value of Tg. By comparing the values of Tg for borehole and surface motions, we find that, contrary to expectation, Tg for borehole motions is usually larger than that for surface motions in most cases. Finally, the conversion equation between the Tg for borehole and surface motions is given using regression analysis.