The relative amplitude method applied to 19 March 1984 Uzbekistan earthquake and its aftershocks

Abstract

The (presumed double couple) source mechanisms of the 19 March 1984 Uzbekistan earthquake and six teleseismically recorded aftershocks down to m b 4.4 (PDE) are determined using the relative amplitude method. It is found that a well-constrained solution for the main earthquake can be obtained when world-wide long-period P wave first motions are combined with constraints on S wave polarisation angles determined from the relative polarities of three component seismograms. Solutions for the aftershocks are obtained from between two and four short period medium aperture array observations of P, pP and sP. The main shock and all but one of the aftershocks give thrust type solutions in broad agreement with each other, their fault planes trending northeast-southwest where the available data provide a constraint on the strike. The remaining aftershock gives a vertical strike slip solution though this conclusion is in need of corroborative evidence. Results for the main earthquake are similar to those obtained by other workers, but it appears that the predominant strike directions of the 1984 aftershocks are different from those previously computed for aftershocks of the 1976 earthquakes, which gave a predominance of northwest-southeast striking fault planes.