The space and time distribution characteristics of the shear stress field for the sequence of the Wuding earthquake

Abstract

Follow Chen and Duda’s model of spectral fall-off of ω³, the dependence of peak parameters of ground motion, peak displacement d _m, peak velocity v _m and peak acceleration a _m, upon the environment stress τ ₀-values are studied using near source seismic digital recordings for the sequence of the Wuding, Yunnan, M=6.5 earthquake, in which, as a new thought, the peak parameters are assumed to be related to the medium Q-value. Three formulae for estimating the environment stress τ ₀-values by the peak parameters of three types of ground motions are derived. Using these formulae, the environment stress τ ₀-values are calculated for the sequence of the Wuding earthquake. The result show that τ ₀-values calculated by the three formulae are constant largely, the averages of τ ₀ are in the range of 5.0–35 MPa for most earthquakes. It belongs to the high-stress earthquakes sequence: the high-stress values are restricted to the relatively small area closely near to the epicenter of the main shock. The fine distribution structure for the contours of the environment stress τ ₀-values is related closely to the strong aftershocks. The analysis of spatial and temporal feature of τ ₀-values suggests that the earthquakes sequence in a rupture process generated at the specific intersection zone of seismo-tectonics under high-stress background.