A STUDY OF ORTHOGONAL AND OBLIQUE RUPTURE PROCESS AND ITS APPLICATION TO THE 1966 XINGTAI EARTHQUAKES

In the paper,the method of studying the orthogonal and oblique ruptures of earthquake source by using spectral amplitudes of P wave is discussed.The theoretical spectral amp-litudes of P wave displacement in far-field of the orthogonal and oblique ruptures which are bilateral or trilateral are calculated and analysed.We Use the grid trial method to determine the source parameters.By using this method,ruptrre processes of the two Xingtai earthquakes witb Ms=6.8 at Malan on March 8.1966 and Ms=6.7 at Dongwang on March 22.1966 are studied.#br#The results show that the rupture of the Malan earthquake is oblique and trilateral with its principal rupture striking NNE and about 29 km in length,and that the NNE end of the rupture is near the region of the main shock of March 22.The rupture of the Dong-wang earthquake is orthogonal and trilateral with its principal rupture striling SSW and about 23 km in length.The other two branches of the rupture are toward NWW and NNE, respectively.The former is in the direction of the main shock with Ms=7.2,occurred 8 minutes later.The latter is in the direction of the Baichikou earthquake(Ms=6.5)occurred 4 days later.Although their lengthes are only 10 km and 6 km,respecticely,they seem to have triggered the two following shocks.The rupture procsses of the two earthquakes mentioned above and the distribution of their aftershocks are very similar.