MOMENT TENSOR AND SOURCE PROCESS OF EARTHQUAKES IN FIJI REGION OBTAINED BY WAVEFORM INVERSION
Supervisor: Yuji YAGI
We evaluated the quality of the local seismic waveform recorded at Yasawa station established by the Mineral Resources Department (MRD, Fiji), and tried to estimate moment tensor solution by using this waveform data. We also estimated moment tensor solution and seismic source process by using teleseismic body wave so as to investigate the faulting system in Fiji region. As for the evaluation of the quality of the waveform recorded at the Yasawa station, we found that EW and NS components were down frequently, and moment tensor solution obtained by 3 components of the Yasawa station is totally opposite to the Harvard CMT solution. This result may suggest that the polarity of the local seismometer components was in a reverse direction and magnification of the seismometer response information is not correct at this stage. We obtained a consistant result when we divided by -10 to observed waveform. Moment tensor inversion analysis was also carried out for 30 events by using teleseismic body-wave downloaded from the IRIS-DMC. Final results are well consistent to Harvard CMT solution. Rupture source process analysis was conducted for the two deep intraslab events that occurred respectively along the Tonga Kermedec subduction zone and two shallow depth events which occurred respectively along the transform fault zones. The rupture processes for the two deep earthquakes are characterized by the rupture propagating mainly along the strike of the fault plane. The two shallow events occurred along the transition zone also characterized by the rupture propagating along the strike of the Fiji Fracture Zone but are controlled by the geometry of the fault.
|Citation: ||Bulletin of IISEE, 43, 13-18.|