台南盆地的地震构造

SEISMOTECTONIC MODEL OF THE TAINAN BASIN,SOUTHWESTERN TAIWAN

由于发生 190 6 ,194 1,194 6 ,1994和 1999年的破坏性地震 ,对台南盆地的地震构造有了更全面的了解 ,并对台湾西南部的活动右旋走滑的义竹断裂有了新的看法 .曾熟知的梅山断裂和新化断裂不是独立的地震断裂 ,它们均属于义竹断裂的分段 .1994年 9月 16日 ,震中在台湾海峡、台南盆地边缘的地震 ,断层面接近东西向 .此地震为台南盆地沉降历史过程中 ,右旋走滑断裂的活动剪裂所导致 .从 194 1年和 1999年地震的主震和微震记录中发现 ,这些菱形分布的地震图像 ,象征走滑断裂双轨构造中的压缩区 .基于上述研究及其它资料表明义竹断裂是台湾西南部重要的构造活动带 。

Thanks to the destructive earthquakes of 1906,1941,1946,1994 and 1999,we have obtained an up-to-date movement picture to understand the seismotectonics of the Tainan basin more fully. This picture is simply a new version of the surface trace of the dextrally mobile Ichu fault,which is of unparalleled importance in the present-day tectonization of southwestern Taiwan. We have learned from the picture that the well-known Meishan fault and Hsinhwa fault are not independent seismogenic fault themselves but particularly active segment of the Ichu fault. The source location of the 16 September 1994 Taiwan Strait earthquake is near the western boundary of Tainan basin. The source mechanism of this event consistently shows a pure normal faulting with striking approximately E-W. It indicated that normal faulting processes induced from the shear of dextral strike-slip faults are active in the historically subsiding Tainan basin.Also found in the same picture is a fault-framed earthquake swarm in which the epicenter of the main shock and many aftershocks of the 1941 and 1999 event were concentrated. Plus,this swarm of the parallelogram shape is structurally a typical contractional strike-slip duplex freshly built up at a double restraining bend of the Ichu fault. All of the above and some other details support our longtime believe that the Ichu fault has been the powerful tectonic motor responsible for the sideways crustal movements in,and the resultant high seismicity of,southwestern Taiwan.