Waveform modelling of the May 20, 1990 Sudan earthquake

Abstract

Very-broad-band seismic waveforms were modelled to derive the moment tensor, the source time function and the depth of the May 20, 1990 Sudan earthquake. Long-period body waves, surface waves and broad-band displacement, recorded by the M edN et regional network, were merged with digital data from global seismic networks, to compare fault geometries obtained by different methods and assess associated uncertainties. Our analysis indicates that the May 20 earthquake had a seismic moment of 5.3 × 10 26 dyne · cm and a depth of about 10 km; the focal mechanism shows a mixture of transcurrent geometry, with one plane striking NW-SE, and a smaller dip-slip component with the T axis oriented in the N–S direction. The fault geometry agrees with models calling for the recent re-activation of the NW-SE trending Aswa transform zone, marking the northern termination of the western branch of the rift. In contrast, the N–S tensional component, which also dominates the focal mechanisms of the aftershocks (Dziewonski et al., 1991), supports the evidence for the rotation of the regional Quaternary stress field to the north, in contrast with simple two-plate models of rifting in East Africa. The Juba event allowed us to test the capability of the M edN et regional seismic network to provide an accurate real-time description of the seismic source.