A DISCUSSION ON THE AMPLITUDE RATIOS OF PP AND P WAVES FOR EARTHQUAKES WITH DIFFERENT FOCAL MECHANISMS

Using the WKBJ approximatation method we calculate the synthetic teleseismograms of P and PP waves to match the observed ones of six large Chinese earthquakes with known focal mechanisms: Xizang earthquake of July 14, 1973; Haicheng earthquake of February 4, 1975; Songpan earthquakes of August 16, 1976, August 21, 1976 and August 23, 1976 and Ninghe earthquake of November 15, 1976. The focal mechanism of the Xizang earthquake is discussecussed to examine the technique used in the calculation.We note that the amplitude ratios of PP and P waves (App/Ap ) have different characteristics for dipslip events and strikslip events within certain epicentral distances. We ca-Iculate the synthetic teleseismograms of P and PP waves for the strike-slip and dip slip events with fault angles of 330, 240 and 0, focal depths of 8 km,, 17km and 24km, at the assumed station with an azimuth of 310 and epicentral distances from 40 to 80. The diagrams of maximum amplitude ratios of PP to P waves (App/Ap) versus distences are given. The possibility to use the (App/Ap) values to give an approximate estimation for the focal mechanism type is discussed. This work may be useful for determining the focal mechanism type for those earthquakes which have only few records such as the Chinese earthquakes from the 1930's to 1960's.