The Studying On The Shallow Seismic Stratigraphy And The Characteristics Of Neotectonic Movement In The Continental Shelf Of The East China Sea

The East China Sea and adjacent regions lie in the margin of East Asian continental and which conclude broad shelf and narrow slope and trench-arc-basin system of the West Pacific Ocean. The Continental Shelf is characterized by shallow water,it has been subsiding and receiving deposits since Cenozoic and sediment source is abundant; Because of the climate alternation since Quaternary, the study area has suffered several transgression-regression cycles and complex oceanic dynamics environment; Neotectonics activities also resulted in the discontinuity of the stratum; Because of the upper factors, the area has characters of sedimentary source diversity, sedimentary structure complication and stratum discontinuity and it is an ideal area to study sedimentary characters, sea level fluctuation, sedimentary environment evolvement and neotectonic movement.The analysis is based on the interpretation of high-resolution shallow seismic profiles, using the method of Seismic Stratigraphy.The Late Quaternary deposit can be divided into 4 sequences including 9 seismic units in the western area and 4 sequences including 13 seismic units in the eastern area.A sequence represent the deposit in a global sea level fluctuation cycle.Therefore,there are 4 transgressions and 3 regressions in the western area, but 4 transgressions and 4 regressions in the eastern area since Late Pleistocene Epoch; According to the principles of sequence and reflection interface identification, the single-channel seismic profiles are interpretated.There are 5 reflective interface and 5 stratigraphic units which are described in detail. Tidal-ridges, paleo-channels, shallow gas, Active faults, pyrogenetic rock and so on are identified from profiles.Some important and significative conclusions are gained from the interpretation of high-resolution seismic profiles and predecessors information,such as: 1) The vertical up-and-down movement of block is intensive in Neotectonic Epoch in the study area and adjacent areas.There are three bigger subsidence centers and one persistent aplift area. The stratum thickness is about 1300m in the Southern bigger subsidence centers and about 1100m in the Northern subsidence center,But in the west uplift area, it is only 19m. The combined effect of the global climate fluctuation and the Neotectonic movement led to the transgression and regression in the East China Sea shelf and adjacent areas in Quaternary.2) The most of the faults within the sedimentary cap rock "rootless faults" don't break the cap rock base, except a small number low-lying border controlled section and the sub-split in the sag. Most of the faults confining the sags are growth faults in the study area and the main strikes are NE,NEE,NW and EW. The successive movement of the faults in Neotectonic Epoch controlled the formation and development of the structural units and the distribution of the late faults; The faults cross areas are the earthquake zones.3) The pyrogenetic rocks of the pre-Neogene mainly distribute in the western part of 123°30′in the study area,only a few distribute in the north and south. The pyrogenetic rocks of the Quaternary occur only in Zhoushan sea area, the pyrogenetic rocks of the Pliocene and Miocene located in southeastern and northern parts of the study area. Magmatic activity has gradually become a new trend from west to east, spatial distribution clearly controlled by NNE-trending fault, the construction of NW-trending also affected the extent and distribution more or less, magmatic activity in space activities, from west to east invaded gradually weakened, eruptive activity continues to increase.4) The Continental Shelf of the East China Sea and adjacent areas can be divided into 3 earthquake cluster zone according to the location of the earthquake epicenter from natural projection point. Earthquakes are mainly distributed in the Yangtze River estuary waters and "X"-shaped in the study area, Combination of faults distribution characteristics of the Yangtze River estuary area, earthquake developed in the fault cross-zone and the stress accumulate and release easily.