Source parameters of the 1987 Edgecumbe earthquake, New Zealand

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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 × 1018 Nm. 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 epicentral distance, to give acomposite 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 ω-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 × 1015 J.