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2007 Vol. 18, No. 4

Display Method:
Geochemistry Characteristics of Sediment and Provenance Relations of Sediments in Core NT1 of the South Yellow Sea
Hong-xia WANG, Xian-jun ZHANG, Xian-hong LAN, Zhi-xun ZHANG, Zhen-hong LIN, Guang-tao ZHAO
2007, 18(4): 287-298.

The contribution of substance from Yellow River, Yangtze River, and Korean rivers to the sedimentation of Yellow Sea is studied through geochemical analysis and through characterization of the source of the substance about sediment from Core NT1 among the lutaceous area in Central South Yellow Sea. The research finds out that the sediment in Core NT1 mainly comes from Yangtze River and Yellow River, the sediment between 0–7.70 m in upper Core NT1 mainly belongs to Yangtze River source; the sediments between 7.70–16.60 m and 42.0–54.80 m in middle Core NT1 are mainly from Yellow River, the 26 m thick sediment interlayer in it mainly comes from Yangtze River; and the sediment between 54.80–69.76 m in the bottom of Core NT1 is mainly from Yangtze River. The results demonstrate that Yangtze River has been playing a main role in the lutaceous area in the Central South Yellow Sea since early Late Pleistocene, and Yellow River started to influence the continental sedimentation of Yellow Sea from early Warm Glaciation of late Late Pleistocene.

The Effects of Applying the Association of Al, K, and Sn in Stream Sediments for Gold Exploration in Different Landscapes
Jin-zhong HE, Shu-zhen YAO
2007, 18(4): 299-309.
Experimental Verification and Research for the Distortion in the Integrated Frequency Responses of the High-Pressure Sealed Cabin and Magnetic Field Sensor
Ming DENG, Wen-bo WEI, Sheng JIN, Gao-feng YE, Qi-sheng ZHANG, Jian-en JING
2007, 18(4): 310-319.

Although magnetotelluric sounding method applied to the land is advanced, there are many difficulties when it is applied to marine environment, one of which is how to lay magnetic field sensors down to the seafloor to complete measurements. To protect the magnetic field sensors from intense erosion and high pressure, suitable high-pressure sealed cabins must be designed to load them. For the consideration of magnetic measurement and marine operation, the sealed pressure cabin should be nonmagnetic and transportable. Among all optional materials, LC4 super-hard aluminum alloy has the highest performance of price/quality ratio to make the sealed pressure cabin. However, it does not mean that the high-pressure sealed cabin made using LC4 will be perfect in performance. In fact, because of its weak magnetism, the pressure cabin made using LC4 has distorting effect on frequency responses of the magnetic field sensors sealed in it. This distorting effect does not affect the use of the magnetic field sensor, but if we want to eliminate its effect, we should study it by experimental measurements. In our experiment tests, frequency sweep magnetic field as excitation signal was used, and then responses of the magnetic field sensor before and after being loaded into the high-pressure sealed cabin were measured. Finally, normalized abnormal curves for the frequency responses were obtained, through which we could show how the high-pressure sealed cabin produces effects on the responses of the magnetic field sensor. Experimental results suggest that the response distortion induced by the sealed pressure cabin appears on mid- andhigh-frequency areas. Using experimental results as standardization data, the frequency responses collected from seafloor magnetotelluric measurements can be corrected to restore real information about the seafloor field source.

High Precision Time Domain Forward Modeling for Crosshole Electromagnetic Tomography
Shu-hai LIN, Li-ying ZHAO
2007, 18(4): 320-325.

To improve the resolution of crosshole electromagnetic tomography, high precision of forward modeling is necessary. A pseudo-spectral time domain (PSTD) forward modeling was used to simulate electromagnetic wave propagation between two boreholes. The PSTD algorithm is based on the finite difference time domain (FDTD) method and uses the fast Fourier transform (FFT) algorithm for spatial derivatives in Maxwell's equations. Besides having the strongpoint of the FDTD method, the calculation precision of the PSTD algorithm is higher than that of the FDTD method under the same calculation condition. The forward modeling using the PSTD method will play an important role in enhancing the resolution of crosshole electromagnetic tomography.

Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau: Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile
Sheng JIN, Gao-feng YE, Wen-bo WEI, Ming DENG, Jian-en JING
2007, 18(4): 326-333.
Research of the Conductive Structure of Crust and the Upper Mantle beneath the South-Central Tibetan Plateau
Gao-feng YE, Sheng JIN, Wen-bo WEI, Martyn Unsworth
2007, 18(4): 334-343.
Application of Reservoir Seismic Inversion to the Damintun Sag in the Liaohe Oilfield
Yun-qing DUAN, Yan-chun WANG, Tian TAN, Wen-jun YANG, Hai-yan GAO
2007, 18(4): 344-349.
The Offset-Domain Prestack Depth Migration with Optimal Separable Approximation
Zhi-fu ZHANG, Chun-yuan LIU, Chun-tao ZHANG, Xiao-hong MENG
2007, 18(4): 350-356.

The offset-domain prestack depth migration with optimal separable approximation, based on the double square root equation, is used to image complex media with large and rapid velocity variations. The method downward continues the source and the receiver wavefields simultaneously. The mixed domain algorithm with forward Fourier and inverse Fourier transform is used to construct the double square root equation wavefield extrapolation operator. This operator separates variables in the wave number domain and variables in the space domain. The phase operation is implemented in the wave number domain, whereas the time delay for lateral velocity variation is corrected in the space domain. The migration algorithm is efficient since the seismic data are not computed shot by shot. The data set test of the Marmousi model indicates that the offset-domain migration provides a satisfied seismic migration section on which complex geologic structures are imaged in media with large and rapid lateral velocity variations.

A Study on the Classification and Well-Logging Identification of Eclogite in the Main Hole of Chinese Continental Scientific Drilling Project
Jian-en JING, Wen-bo WEI, Sheng JIN, Gao-feng YE, Ming DENG
2007, 18(4): 357-365.

Eclogite, one of the important lithologies in the main hole of the Chinese Continental Scientific Drilling (CCSD) Project, exists above the depth of 3 245 m and has distinctive responses of gamma-ray, compensating density and neutron well-logging, and so on. In this study, according to the diversities of minerals and chemical components and well-logging responses, eclogites are classified from three aspects of origin, content of oxygen, and sub-mineral. We studied the logging identification method for eclogite sub-classes based on multi-element statistics and reconstructed 11 kinds of eclogite. As a result, eclogites can be divided into 6 types using well logs. In the light of this recognition, the eclogite in the main hole is divided into 20 sections, and the distribution characters of all sub-classes of eclogite are analyzed, which will provide important data for geological research of CCSD.

A Preliminary Study on Paleomagnetism and Rock Magnetism of Eclogite from the Maobei Area
Xiao-hong MENG, Qin-fan YU, You-zhao GUO, Yao-xiu ZHOU
2007, 18(4): 366-374.