Assessment Of Crustal Stability Of The Three Gorges

The assessment of crustal stability of the Three Gorges area was made from a study of the tectonic evolution and the present tectonic stress field and a seismic risk analysis. The principle of system engineering and Fuzzy judgement vere applied. The following principal conclusions result.1. The area had undergone six stages of tectonic evolution: basement formation, N-S pull-apart of the basement, cover formation, cover detachment, N-S crustal shortening and nearly E-N extension.2. The present tectonic stress field of the area reflects a N-S compression resulting from the activity of the Neocathaysian structural system. The fastest faulting took place in the middle-late Pleistocene. Ground deformation mapping showed uniform vertical crustal movement with no significant difference in elevation. Finite element modelling gives a relatively uniform stress distribution without remarkable stress concentration.3. The level of seismicity is lov. The past earthquakes had mostly a magnitude of 5 or so. Each seismic belt has a higher b value. 6 potential earthquake sources and their seismicity parameters are given.The probability of exceedence of acceleration peak value is calculated for 50,100 and 200 years.The dam-reservoir area does not exceedâ…¦. For a nuclear power station design, an intensityâ…¦can be used to ensure security for a probability of exceedence is 1ï¼…within 100 years.4. A zonation of crustal stability of the area is presented, which is classified as stable, relatively stable and less stable. The dam area falls in the stable zone.