Analysis on EarthquakeInduced SoftSediment Deformation Structures in the Cambrian Dachenling Formation in the Tongcun Village,  Zhejiang Province

Key words: 
• paleoseismic /
• soft sediment deformation /
• driving mechanism /
• Cambrian in the west of Zhejiang province /
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Abstract: Soft sediment deformation is one of the key indicators identifying the existence of paleoearthquake. Based on the standard as the sediments suffer the earthquake,fliud pressure changing degree and the strength of the liquefied. Through three horizons of soft sediment deformation events with earthquakedriven on the Cambrian Dachenling Formation in the Tongcun village  in Zhejiang province, the abundant soft sediment deformation are seismic microfractures, microfolding and liquefied structures. They reflect  the extent of the fliud pressure changing and the strength of the liquefaction, when the sediments suffer  from the earthquake. 
  The microfoldings in the profile of Tongcun village always place there, and are symmetrical folds and uniform liquid layer. Its tectonic features do not match significantly to the landslide deformation, and the author and other measure the microfolding axial plane randomly in the profile of Tongcun village, and get total of 39 sets of data, and then correct in level for statistical analysis. After all the work, the author rules out the possibility of landslide.
  Liquefied structure is a kind of the geological phenomenon of conservation of matter and transfer of form, and it shows the flow structure when liquefaction invades. The formation of liquefied form caused by three reasons, which represent the diffferent stages of devolatilization. The auther researchs by contrasting among the liquefied structures by means of four aspects of section characteristics, surface features, contrasting with surrrounding rock, and symbiotic construction.
  By observing and counting about special characteristics and properties of event horizons of the soft sediment deformation, and distinguishing the similar structures without earthquakedriven, these indicate that earthquake was the driven force. The discovery of three seismite events layers indicated that the deposition period of Dachenling formation is the period of paleoseimic occuring frequently.Paleoseismic induces the formation of KaihuaChun'an major deslocation, so the author and other consider deposition time of the event layer Ⅱ is the strong activing period of the formation of KaihuaChun’an major deslocation. Counting the seismic disturbance and epicentral distance in the three events layer estimate the layer Ⅱ and layer Ⅲ magnitude are 67 level and about 6 level, and the autherand other preliminary view that the layers without the earthquake zone maybe exist molan tooth. So, the identification mark and lithological sequence of seismite get perfect, the understanding get deepening about the sedinentation of cambrian Dachenling formation resulting from seismic events in the west of Zhejiang province.