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 co 3, the dependence of peak parameters of ground motion, peak displacement dm, peak velocity Vm and peak acceleration am, upon the environment stress r0-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 r0-values by the peak parameters of three types of ground motions are derived. Using these formulae, the environment stress to-values are calculated for the sequence of the Wuding earthquake. The result show that to-values calculated by the three formulae are constant largely, the averages of ro 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 to-values is related closely to the strong aftershocks. The analysis of spatial and temporal feature of to-values suggests that the earthquakes sequence in a rupture process generated at the specific intersection zone of seismo-tectonics under high-stress background.Key words: digital seismogram peak parameters of ground motion near-source environment stress characteristics seismic sequence of Wuding earthquake *