Comparison of the rupture and radiation characteristics of intermediate and deep earthquakes

We study the depth dependence of the rupture and radiation characteristics of earthquakes below 70 km depth by investigating the source properties of intermediate (70 - 300 km depth) and deep (> 300 km depth) earthquakes along the Fiji and Japan subducting slabs. The source properties are explored by retrieval of the moment rate functions and by spectral analysis, using P waves. Thirty-two earthquakes in the period 1986-1997 with seismic moment > 1. x 10(18) N m are analyzed. The main conclusions are (1) the dependence of the source duration on the scalar seismic moment M-0 follows the usual one-third trend, on average; (2) this behavior is still visible when the source durations are adjusted for the shear wave velocity and the modulus of rigidity at the hypocentral depth; (3) the effective stress drop and the effective strain drop for subcrustal earthquakes in Fiji and Japan tend to be larger than those for the crustal ones; (4) the duration and shape of the moment rate functions do not show any systematic difference between intermediate and deep events; and (5) no obvious difference in the spectral properties of intermediate and deep events is seen.