Note on the azimuth deviations ofP-waves recorded at Djakarta station

Summary Differences between epicenter azimuths and the direction of arrival of firstP-waves are determined from the horizontal seismograms of Djakarta station. Systematic azimuth deviations of more than 15° are encountered in the NW through N to SE azimuths. Azimuth deviations caused by a discontinuity dipping 5, 10 and 15° and with a ratio of velocity of longitudinal waves at either side of the discontinuity of 1.23, 1.38 and 1.52 are calculated. The most simple model suitable to the observed data is that of a discontinuity with a velocity ratio of about 1.5, dipping 8–10° in a N 10° E direction. In the S and W directions of Djakarta no dipping discontinuity is needed to account for the few observed data in these quadrants.