Relative Moment Tensor Study of deep earthquake clusters in the Tonga-Fiji Subduction Zone

Abstract:

Studies of sources mechanisms play an important role in deep earthquake research. Moment tensors are usually estimated by the least-square fitting of amplitudes in the observed seismograms. In this study, we apply a relative moment tensor procedure to study the clusters of the deep earthquakes. The relative moment tensor procedure inverts the moment tensors of clustered events at the same time using the amplitude ratio of the seismic phases recorded at same station generated between the events and the information of take off angle and azimuth of the seismic phases. The relative method has some advantage over the traditional moment tensor inversion methods: 1) no Green's function is needed and 2) using the relative amplitude between the events eliminates the inaccuracies of the Green’s functions because the seismic waves share similar ray paths between the cluster events. We use the relative method to study the source mechanisms of deep earthquake clusters in Tonga-Fiji subduction zone. We discuss the difference between our results and those of traditional studies, and its implications to the understanding of deep earthquake mechanisms.