Source parameters of the 1987 Edgecumbe earthquake, New Zealand

Abstract

Moment tensor inversions of low-frequency teleseismic surface-wave and body-wave data for the 1987 March 2 Edgecumbe earthquake, New Zealand, give an average seismic moment of 7.0 X 10 18 N m. Measurements of seismic moment at low frequencies are converted to spectral levels normalised to 10 km distance and combined with the acceleration spectrum from a strong-motion seismogram recorded at about 15 km epicentraldistance, to giveacomposite source spectrum for the main shock covering more than four decades in frequency. The source spectrum shows a constant low-frequency level, a comer frequency of 0.22 Hz, and a high-frequency slope of approximately ro-2 . The comer frequency implies a fault radius of 6 km giving an average fault displacement of 2 m and a stress drop of 5 MPa. Integration of the velocity-squared spectrum indicates an energy release of 1.1 X lOIS J.