CHARACTERISTICS OF CODA WAVE OF THE LOCAL EARTHQUAKES IN SHANXI REGION

The coda wave features of small earthquakes recorded by the shaanxi seismic network have been investigated by using Aki's coda wave theory. The result in dicates that tile decay curves of coda amplitude are almost parallel to each other irrespective of its differences in the epicentral distance, and the coda amplitudes are onIy related to the geological condition around the station in rhea certain scope. The theoretical nomograms of short period seismograph DD-1 and the coda wave decay curves have been illustrated in terms of the singIe baekscattering model, from which the average frequencies and the distribution of Q vaIues for 11 stations have been estimated,. The Q vaIues range from 108 to 230 with an average 170 between 1.19 and 1.59 Hz. Finally some seismic moments of small earthquakes in shaanxi have been computed by using the empirical formul of coda amplitude and seismic moment in Alaska, furthermore an empirical reIationship between moment and magnitude has been got and compared with that in the other regins.