THE 14 NOVEMBER 1986 TAIWAN EARTHQUAKE - AN EVENT WITH ISOTROPIC COMPONENT

Investigating the possibility that some earthquakes may significantly differ from the double-couple mechanism is always a subject of concern to seismologists. In this paper we give a detailed study of the 14 No vember 1986 Taiwan earthquake (M(s) = 7.8) using the long-period body- wave waveform inversion. A hybrid global inversion method was used to derive the best-fitting solution and estimate the extreme models of no n-double-couple components. The regional P-waveforms provide high reso lution to the isotropic component. The inversion result shows that the Taiwan earthquake is an event composed of the reverse dip-slip disloc ation source and an isotropic component. A notable source parameter in the result is the relative intensity of the isotropic component, whic h is defined as S-P = (sigma(1) + sigma(2) + sigma(3))/3M(0), where si gma 1, sigma 2 and sigma 3 are the eigenvalues of the seismic moment t enser with sigma 1 > sigma 2 > sigma 3 and M(0) = (sigma(1) - sigma(3) )/2. The best-fitting solution of S-P is - 0.33, and the extreme value s of S-P are - 0.48 and - 0.13, respectively. This result suggests the existence of an obvious compressional isotropic component at the sour ce process of this event.