| Soft sediment deformation is one of the key indicators identifying the existenceof paleo-earthquake. Based on the standard as the sediments suffer the earthquake,fliudpressure changing degree and the strength of the liquefied. Through three horizons of softsediment deformation events with earthquake-driven on the Cambrian DachenlingFormation in the TongCun village, in Zhejiang province, the abundant soft sedimentdeformation are seismic micro-fractures, micro-folding and liquefied structures. Theyreflect on the extent of the fliud pressure changing and the strength of the liquefied, whenthe sediments suffer the earthquake.Seismic micro-fractures not only development individually, but also occur in groups toform a ladder-like or others. On the Cambrian Dachenling Formation in the TongCunvillage, in Zhejiang province, Fault’s scale is small, space is also small, angle which ismuch at60°-70°is steep, fracture surface is relatively flat. Fault which is limited to thelayer growth and isn’t conjugate is the tensile fracture. Micro-fractures become more andmore slender and less or uniform distribution. Its fracture surface fill with plaster.Micro-folding include micro-folding laminae and deformed laminae related toliguefied layer. The angle between micro-folding and layer is moderate. Micro-folding’sdevelopment is small, irregular and uncoordinated. Micro-folding are all deformed in layer.In the vertical it mainly shows the deformation layer is located in the upper and lower sidesholding in undeformed sedimentary layer, but micro-folding is differert with structural foldand looks more disorder. The micro-foldings in the profile of TongCun village alwaysplace there, and are symmetrical folds and uniform liquid layer. Its tectonic features don’tmatch significantly to the landslide deformation, and the author and other measure themicro-folding axial plane randomly in the profile of TongCun village, and get total of39sets of data, and then correct in level for statistical analysis. After all the work, the authorrules out the possibility of landslide.Liquefied structures consist escaping structures and liquefied dikes structures.Escaping structures display two forms, but liquefied dikes are not seen in escapingstructures. This phenomenon indicates that this structure is emerged by the non-seismicfactors. Liquefied dike is emerged by the escaping structures’s layer movement, and all hasthe mother rock or layer of liquid source. Many laminated limestone in the field ischaracterized by thick layer and doesn’t show the laminae, but it is very chear under themicroscope. Liquefied structure is a kind of the geological phenomenon of conservation of matter and transfer of form, and it shows the flow structure when liquefy invades. Theformation of liquefied form cause by three reasons, which represent the diffferent stages ofdevolatilization. The auther researchs by contrasting among the liquefied structures bymeans of four aspects of rock and the structure characteristics, energy spectrum analysis,and Sr,C,O isotope analysis.In addition, deformational structures with unearthquake-driven on the CambrianDachenling Formation in the TongCun village have escaping structure, tuberculosis, slotmold and load structure.By observing and counting about special characteristics and properties of eventhorizons of the soft sediment deformation, and distinguishing the similar structures withoutearthquake-driven, these indicate that earthquake was the driven force. The discovery ofthree seismite events layers indicated that the deposition period of Dachenling formation isthe period of paleoseimic occuring frequently.Paleoseismic induces the formation ofKaihua-Chun’an major deslocation, so the auther and other consider deposition time of theevent layer Ⅱ is the strong activing period of the formation of Kaihua-Chun’an majordeslocation. Counting the seismic disturbance and epicentral distance in the three eventslayer estimate the layer Ⅱ and layer Ⅲ magnitude are6-7level and about6level. Throughto Sr, C,0isotope characteristics of abnormal, we found that the tsunami influence thesedimentary deposits in the stage of Dachenling, and found the earthquake liquefaction andsoft sedimentary deformation happen near the surface, and liguefied dike has the pulsebody sedimentary characteristics of terrestrial detritus So, the identification mark andlithological sequence of seismite get perfect, and the point of the views of thegeochemistry provide evidence for the earthquake source of liguefaction. Theunderstanding get deepening about the sedinentation of cambrian Dachenling formationresulting from seismic events in the west of Zhejiang province. |
PDF Full Text Request