We conducted moment tensor determination for 27 events that occurred in the North Fiji Basin from
2015 – 2022 with a magnitude of Mw > 4.0 and depths less than 350 km. We used seismograms from
seismograph stations in Fiji and the neighboring countries. We used a regional velocity model with a
10-km thick crust by Xu and Wiens (1997) to compute Green’s functions. Focal mechanism solutions
were then validated in reference to the Global Centroid Moment Tensor (GCMT) solutions. We found
that the solutions obtained by the present study are generally consistent with the GCMT solutions in
terms of focal mechanism and moment magnitude. Stress axes of the focal mechanisms are consistent
with tectonic process reported by previous studies. Focal depths were shallower than the GCMT centroid
depths by 1.4 km in average. We also evaluated an effect of velocity model on focal mechanism solutions
by comparing waveform fitting and similarity to GCMT. We performed the moment tensor inversion
for events with Mw > 5.0 using the original regional model, its modified model with a 20-km thick crust,
and a global standard model. For most of the events used for comparison, the waveform fitting is best
for the original regional model with a 10-km thick crust than the other two velocity models. We
compared focal mechanisms determined from data including and excluding stations from the
neighboring countries. The comparison shows that the mechanisms are closer to the GCMT by including
data from neighboring countries, suggesting the importance of international data exchange.
Keywords:
Moment Tensor, Fiji, velocity model