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由海啸波形的反演估算了1946年南海地震(Mw8.3)断层面上的同震滑动分布。比以前的研究(Satake,1993)有以下3个方面的进展:(1)使用了大量的较小次级断层;(2)次级断层更拟合板块的几何形状;(3)应用了更详尽的探测数据。反演的结果表明,实测波形和合成波形间的一致性比以前的研究有极大改善。在四国近海震源区西半部,在闭锁区下倾端附近发生了约6m的大滑动。上倾或浅部的滑动很小,说明该地区为弱的地震耦合。在纪伊半岛近海震源区东半部的约3m的大滑动延伸到整个闭锁区。由大地测量数据(Sagiya and Thatcher,1999)估计了上板块八字形断层上的大滑动,对于解释海啸波形并不需要这样大的滑动,表明这些大的滑动是无震滑动。板块界面下倾端上的两个滑动分布,一个是由大地测量数据得到的,而另一个是由海啸波形得到的,除了在四国室户角下的滑动外,两个滑动分布都相当一致。据此来看,无震滑动也发生在室户角下部的板块交界处。
From the inversion of the tsunami waveform, the coseismic slip distribution on the fault plane of the 1946 South China Sea earthquake (Mw8.3) was estimated. Compared with the previous study (Satake, 1993), there are three advances in the following aspects: (1) a large number of smaller sub-faults are used; (2) sub-faults more fit the plate geometry; (3) Detailed exploration data. The inversion results show that the consistency between the measured waveform and the synthesized waveform is greatly improved compared with previous studies. In the western half of the source region of the four countries near the sea, a large slip of about 6 m occurred near the downslope of the closure area. Slippage in the updip or shallow areas is small, indicating weak seismic coupling in the area. A large slide of about 3 m in the eastern half of the Seismic peninsula near the Kii Peninsula extends into the entire closure area. Sagiya and Thatcher (1999) estimated the large slip on the eight-plate fault of the upper plate and did not require such a large slip to explain the tsunami waveforms, indicating that these large slip are slip-free. Two slip distributions on the downtilt of the plate interface, one from geodetic data and the other from tsunami waveforms, are quite consistent except for slippage at the quadrangular compartment. From this point of view, the earthquake-free slippage also occurs at the junction of plates at the lower part of the Habitat Corner.