THE EFFECTS OF THE CALIBRATION FUNCTION,AZIMUTHS AND SITES OF THE STATIONS AND DIFFERENT METHODS OF APPROACH ON THE MAGNITUDE DETERMINATION OF NEAR EARTHQUAKES, ML

The effects of the calibration function, the azimuthal angles of the stations relative to the earthquakes, the ground conditions of the station sites and also the different methods of approach on the magnitude determinations of near earthquakes ML have been studied. The results are as follows:(1) A new calibration function R3(△) can be found for southwestern China better than the original ones R1(△) and R2(△).(2). Due to the azimuthal variation of wave radiation, magnitude determinations at stations located in different azimuths differ by about 0.3-0.5 in ML. Proper combination of P and S waves can reduce to certain extent the azimuthal effect.(3) Corrections for the station sites on bed rocks are relatively small. However, some larger correction values may be attributed to erroneous magnification values of the seismographs.(4) Besides using horizontal components of the S-wave, the vertical component of S-wave and the horizontal and vertical components of the P-wave, multiplied by appropriate factors may also be used for determining the local magnitude ML, giving nearly the same values as the ordinary method.