A measuring study for single-trace Lg coda Q(Lg)(c)

A stacked spectral ratio method is applied to the measurement of Lg coda Q( Lg)(c) at regional epicentral, distances (Delta < 500km). In order to test the stability and reliability of the method, we select two sets of high sig nal to noise ratio seismic records at different regions. One set is Lg coda time series from the Beijing telemetry seismic network observed 15 aftersh ocks of the Datong principal earthquake on Oct 18, 1989 (M-L = 5.9). Other set is from the portable digital seismic network observed two earthquakes i n Pingliang, Gansu province. The source parameters basically are same among every set of earthquakes, that is to say, their ray paths to the given sta tion are almost same. So obtained Q(Lg)(c) can be regarded as an average at tenuation effect over the paths, which is not affected by the sources. The measuring Q(Lg)(c) results show that: (1) Although there are different inst ruments used in two seismic networks with different observation conditions in every stations, fitting results of the Q(0) and eta are highly linear. I t indicates that the SSR method is stable. (2) There are the basically same results of Lg coda Q(Lg)(c) at a given station observed different earthqua kes of the same set, i,e. Q(0) and their average values are almost within t he range of the standard error. It indicates that the SSR method is reliabl e. (3) Based on the measuring results of Lg Q(Lg)(c) at different stations recorded the same earthquake, it can be seen that there is obvious differen ce, which can be regarded as the lateral difference of the tectonic structu re, on Lg coda Q(0) passing through different tectonic area. So if we selec t some earthquakes with a good azimuth distribution and there are a proper station distribution, we can image on Q(Lg)(c) in the study area using meas uring Q(Lg)(c).