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 November 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 non-double-couple components. The regional P-waveforms provide high resolution to the isotropic component. The inversion result shows that the Taiwan earthquake is an event composed of the reverse dip-slip dislocation source and an isotropic component. A notable source parameter in the result is the relative intensity of the isotropic component, which is defined as S_P = (σ₁ + σ₂ + σ₃) 3M₀, where σ₁, σ₂ and σ₃ are the eigenvalues of the seismic moment tensor with σ₁ > σ₂ > σ₃ and M₀ = (σ₁ - σ₃) 2. The best-fitting solution of S_P is -0.33, and the extreme values of S_P are -0.48 and -0.13, respectively. This result suggests the existence of an obvious compressional isotropic component at the source process of this event.