科研之友
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摘要
Determining focal mechanisms of small or micro-earthquakes is very. important but difficult in seismological research, and no method has been commonly accepted and widely used due to complexity of this problem itself till now. In our previous paper we proposed an inversion technique, named generalized polarity and amplitude technique (GPAT), and the feasibility and capability of resisting disturbance of the technique has been tested with a series of numerical experiments. In this paper we present the examination of the practical ability of the GPAT by means of forty-nine real earthquakes. The GPAT employs polarities of the P-wave first-motion and the maximal amplitude with polarities. The phases used here are generalized, which are no longer limited to well-known P-waves, S-waves or surface waves. The maximal amplitudes can be adopted as long as they are clearly recorded in spite of the well-known phases. GPAT uses the correlation coefficient between observed data and synthetic data as the objective function, and sets a weight factor for the firstmotion polarities and the maximal amplitudes. In this paper we select forty-nine earthquakes with epicenter distances from 5 km to 8000 km, with magnitudes from M(L)0. 2 to M(S)7. 0, including six far-field events in and surrounding China, twelve regional events in Lushan, Sichuan, eight local events in Yingjiang and twenty-three local events in Qiaojia, Yunnan. The focal mechanisms of the far-field events determined with GPAT are highly consistent with those from GCMT(Global Centroid Moment Tensor). The focal mechanisms of the regional events determined with GPAT are consistent with those from other studies, and they appear to be similar to each other. For the local events in Yingjiang, the focal mechanism of the main shock is consistent with those from other studies and other events have the mechanisms fairly similar to the main shock. For the local events in Qiaojia, they all have similar strike-slip mechanisms. Moreover, the moment magnitudes from the GPAT are reliable, but the focal depths from the GPAT seem to be about 0. 6 km deeper than the routinely determined depths on average. The GPAT is proved to have a good performance in the inversion for focal mechanism, moment magnitude and focal depth. It is not only suitable for far-field data, but also for regional and local data. It is not only suitable for moderate-size events, but also for small and micro events.
- 出版日期2015-10
- 单位中国地震局
