SEISMIC ENERGIES OF EARTHQUAKES AND RELATIONSHIPS TO OTHER SOURCE PARAMETERS

An advanced method is presented to calculate the energy of teleseismic events by integrating the power spectra of P-and S-waves. The algorit hm takes into account proper corrections for radiation pattern and ane lastic absorption in the mantle. From theoretical considerations, near -field source spectra and the partitioning of P-and S-wave energy a fr equency-dependent Q(omega)-model was derived. It is a combination of a global frequency-independent Q(z)-model developed by Anderson and Har t (1978a,, 1978b) and a power law for frequency with exponent gamma = 0.23 at a reference frequency f(0) = 0.1 Hz. The method was applied to shallow and deep earthquakes in Tonga-Fiji, Vanatu and the New Britai n region, recorded by broadband stations of the GEOSCOPE network. The resulting energies are compared with m(b), M(s) and the seismic moment s M(0) of each event. In addition, 9 events at the Honshu and Kuriles subduction zone, recorded at the Grafenberg array, were investigated a nd apparent stresses were computed from energy and seismic moment. The results suggest a systematic increase of apparent stress with depth o f the subducted lithosphere, starting from approximately 20 bars for s hallow events to 250 bars for depths of 200-300 km. The two lowermost events (500-600 km) show a decrease of apparent stress down to 2-15 ba r.