Study Of Shallow Water’s Characteristics Based On Marine Seismology

Seismic oceanography is a new detection technology of seawater. Direct CTDmeasurment is a traditional method with high vertical resolution and low horizontalresolution. Multichannel seismic imaging shows thermohaline and densityfinestructure over much the whole ocean depth with a high horizon resolution of theorder of10m. Multichannel seismic can provide a highly informative snapshot of thethermonhaline features at a specific time. Now most of the study of Seismicoceanography focuses on the deep sea with large scale phenomenon of physicaloceanograpy at home and aboard. Shallow sea is the place where human beingsactivities frequently. Research of thermoline in shallow sea has important significanceof marine environment change, maritime communications and marine militarysecurity.Shallow water is complicated and variable. Based on the theory of physical marine,the temperature (density) depth model is created. The acoustic velocity calculatedby Wilson formula is used to creating the velocity depth model. The paper studiesthe wave filed characters of shallow water by seismic modeling. Temperatureinversion results show the feasibility of inversing physical parameters from seismicdata. Through the study of small multichannel high precision measurement system,the author derives seismic profiles with high precision of shallow sea water, whichensure the high resolution, high signal-to-noise ratio and high-fidelity condition.Based on the analysis of seawater characteristics in shallow sea, the paper carry outthe study of seawater Seismic data interpretation and put forward the technology ofthermohaline finestructure description. The author obtains four results and innovation.(1) The study of seismic modeling and wave field characteristics. Based on theresearch of physical modeling, the paper creats two different model of seawater thermohaline and carry out the forward modeling, then analyzes the seismic wavefield characteristic of shallow sea water. Using the reflection seismic data which wasprocessed, the paper inversion the physical characteristics of the sea water, and provesthe feasibility of seawater physical parameters inversion from seismic data.(2) Research of technology of small multichannel high precision measurement system.The wave impedance of shallow seawater is smaller than strata, and the environmentof shallow is unstable, and the detection of seawater layer is difficult. In allusion tothese features, the paper study high resolution detection technology which is suitablefor detecting shallow seawater. Small multichannel seismic acquisition systemintegrates the merit of shallow seismic profile and the advantage of large multichannelseismic system, and brakes through the limit of seismic acquisition in shallow sea.3A set of methods that describes the fine structure in the shallow water is made,including sea water layer calibration technology, the standardization of structures ofregional temperature and salinity, the inversion of temperature, salinity, density usingseismic reflection data, and3D explanation of temperature and salinity structure ofsea water. Using the technology to conduct a detailed study of the water structure inthe Bohai Bay, it shows that the sea water in the Bohai Bay divided into two types inthe horizontal direction: the water masses which are near the shore and the watermasses which are far from the shore. In the vertical direction, the coastal water massesin depth of20m or less are mixed basically; the water mass far from the shore aredivided into three layers, and the upper one is mixed water. There is a transitionregion between the two kinds of water masses, an ocean front structure which has thehorizontal width of about1km in the shallow water is found.4Based on the theory of shallow water deposition, the paper makes a study aboutthe influence of deposition by the shallow water. Waves, tides and currents are themain hydrodynamic conditions affecting the shallow water deposition. The maingeological effects of waves include the transformation of seabed, the erosion of bedrock coast, and the transportation and redeposition of nearshore sediments. Thescope of its role is mainly in the upper part of the continental shelf. The maingeological processes of tides include the erosion, transportation and redeposition ofthe sediment. In different coast environment the processes are different. Thegeological process of rivers is transportation. With the analysis of sedimentarycharacteristics of Bohai Bay area, we can point out that the main water dynamicconditions here are tide, wave and storm surge, ocean current is the mainhydrodynamic force to maintain the deep groove structure.