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Yang J.-Y.,CAS Qingdao Institute of Oceanology | Yang J.-Y.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Zhang X.-H.,CAS Qingdao Institute of Oceanology | Zhang X.-H.,Function Laboratory for Marine Mineral Resource Geology and Exploration | And 3 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

Multi-source gravity data including measurements on land, shipboard surveys, satellite altimetry, Bouguer gravity anomalies and EGM2008 global gravity model data are collected and analyzed for compiling the freei-air gravity anomaly map on the scale of 1:5000000 in the land and seas of China and adjacent areas. The data merging and integration method is established based on analysis of the accuracy and resolution of different sources of gravity data. Evenly distributed land gravity data could be gridded in flat land areas. A synthetic method using Bouguer gravity and high precision topographic data to calculate the free-air gravity data is proposed to fill the land areas where the gravity measurement is hardly or impossible to implement due to complex terrain. Data comparison between the synthetic free-air gravity data, measured data and EGM2008 data proves that using the synthetic data is a better choice for filling the areas lacking real data. This method is also applied to the continental and island areas outside mainland China where there are no real data collected. The STD analysis method is applied to the northern part of the South China Sea to compare the accuracy of three independent gravity data, the shipboard gravity data and two kinds of satellite altimetry derived gravity data, the SS series from Scripps, US and DNSC08GRA from DTU, Denmark.SS V18.1 and DNSC08GRA data, which show very good consistence in terms of accuracy and resolution.The standard deviation of the two kinds of satellite gravity data in the SCS is less than 2mGal, which is a major improvement compared with the former SS V16.1.With the rectification of shipboard gravity data, the wide coverage of satellite gravity data could be used for small-scale free-air gravity mapping. In the coastal zone, the EGM2008 global potential model is used as a reference field providing a seamless gravity transition from land to ocean. Wavelet transform and multiscale analyses are applied to decompose the free-air gravity field in China and its adjacent areas to help the gravity field interpretation. Eight anomaly areas are confined by three horizontal and four vertical first-order gravity gradient belts. Anomaly subareas and the second-order gravity gradient belts are delineated in the gravity field to provide evidence for establishing the tectonic framework in the block tectonic scheme. ©, 2014, Science Press. All right reserved.


Wang X.,CAS Qingdao Institute of Oceanology | Wang X.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Luan X.,CAS Qingdao Institute of Oceanology | Luan X.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Zheng J.,Sinopec
Shiyou Diqiu Wuli Kantan/Oil Geophysical Prospecting | Year: 2015

We propose in this article a method for P wave reflection coefficient approximation. Based on the accurate Zoeppritz equation of viscoelastic medium and the viscoelastic medium, we use the approximation of weak viscoelastic medium and similar medium to derive reflection coefficient approximate formula of viscoelastic medium according to the theory of decomposition of medium. The approximate formula is divided into real part and imaginary part. The elastic and viscoelastic terms are all in the real part, which more accurately reflects the wave propagation in the actual formation. In particular, when the quality factor is infinite and the attenuation angel is zero, the reflection coefficient approximate formula is completely consistent with the reflection coefficient approximate formula in the elastic medium (Aki-Richards approximate formula), which proves the rationality of the formula. Finally, the validity of the reflection coefficient approximate formula of viscoelastic medium is verified with the four kinds of AVO models and different viscoelastic parameters. The results show that the P-wave reflection coefficient approximate formula with the background of viscoelastic medium has higher precision than Aki-Richards approximate formula. © 2015, Science Press. All right reserved.


Shang L.,Ocean University of China | Shang L.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Shang L.,Institute of Marine Geology | Shang L.,CAS Qingdao Institute of Oceanology | And 11 more authors.
Studia Geophysica et Geodaetica | Year: 2016

In September and October of 2011, a marine magnetic survey was conducted in the southern East China Sea between 120° and 126°E, 26° and 28°N with the research vessel Kexue-3. New magnetic maps with 5 × 5 km grid spacing were generated after meticulous data processing. Based on an analysis of magnetic anomaly features and further calculation results, including the total horizontal derivatives (THD), second order vertical derivatives (SVD) and analytic signal amplitude (ASA), several new tectonic insights on magnetic sources, basement structures and fault properties were obtained. The NE-SW or NNE-SSW oriented magnetic anomaly highs have different sources: (1) The high amplitude, short wavelength magnetic anomalies of the Zhemin Uplift are caused by shallow buried igneous rocks intruded along NE-NEE oriented faults. (2) The high amplitude, moderate wavelength magnetic anomalies of the Diaoyudao Uplift are caused by the metamorphic basement intruded by magmatic rocks. (3) The magnetic sources of the Yandang Uplift and Taibei Uplift in the shelf basin are shallow buried metamorphic basements and deep buried volcanic bodies, respectively. Several NW-SE or NWW-SEE oriented dextral strike-slip fault belts were identified as important tectonic boundaries. Each is composed of several en echelon and partly overlapping secondary faults. Initially formed in the Cretaceous, these fault belts have evolved through multiple periods, propagated seaward with the migration of the basement rifting and accommodated local stress fields in the Cenozoic. © 2016 Institute of Geophysics of the ASCR, v.v.i


Wu Z.-Q.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Wu Z.-Q.,CAS Qingdao Institute of Oceanology | Hao T.-Y.,CAS Institute of Geology and Geophysics | Zhang X.-H.,Function Laboratory for Marine Mineral Resource Geology and Exploration | And 6 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

Many geologists have studied the contact of the Yangtze block and North China block in the sea area with regional geological and geophysical methods. There are still different understandings. Combining regional geological data, we analyzed the contact relationships between these two major tectonic blocks in the sea area by acquisition, processing and analysis of multi-channel seismic data in the South Yellow Sea. According to the seismic geological conditions and exploration target, we designed a new air-guns array pattern of upper/lower sources which can effectively attenuate the effect of ghost in the low frequency range, broaden the bandwidth of seismic signal and promote the energy of low frequency components, based on the advantage of the large penetration depth and long pathways for low frequency signal. For the exploration target layer of weak seismic reflection characteristics, we used long cable method receiving strong wide-angle reflection signal. The long spread of wide-angle reflection receiving method was used considering poor reflection in the target layer interiors, which permitted to achieve the strong energy wide-angle reflection at the large offset. The time-distance curve of wide-angle reflection with large offset is clear non-hyperbolic, which is difficult to focus on the effective stack data. We adopted the normal moveout correction of wide-angle reflection which was based on the anisotropic and the pre-stack time migration processing to achieve the impactful NMO, stacking and imaging of wide-angle reflection. We obtained the deeper effective reflection that was below the continental sedimentary layer with the application of new seismic exploration technology. According to the seismic reflection characteristics and the regional geological background, the seismic reflection events in the southern Yellow Sea basin can be divided into four seismic reflection sequences in the new seismic imaging section. There are the Cenozoic continental facies seismic reflection sequence (S1), Mesozoic continental facies seismic reflection sequence (S2), Mesozoic-Paleozoic sediments seismic reflection sequence (S3) and basement seismic reflection sequence (S4). The S4 represents the Pre-Sinian metamorphic strata reflection and S3 is similar to marine facies strata seismic sequence calibrated by well data in the southern depress. It was another evidence for the speculation that the northern depression developed with Mesozoic-Paleozoic marine carbonate strata, characterized by large buried depth, great thickness and widespread distribution. In the Qianliyan fault, S4 seismic reflection sequences are underlain by that of S3, where a tectonic zone extends in direction of NE-SW. We conclude that there is a nappe structure zone trending NW-SE as shown by the synthetic interpretation of seismic, gravity and magnetic data. This zone distribution area was about 5000 km2 in the basin south of Qianliyan fault, about 100 km distant to the biggest nappe, and the buried depth was about 3500~7500 m. This nappe structure zone developed in the north of northern depression and uplift area north to the Qianliyan fault. The present and previous results show that the Qianliyan uplift was the contact zone between the North China block and the Yangtze block. The Yangtze block moved northward, which was embedded in the North China block after the continent-continent collision of the two blocks. The contact model between the two blocks is like a “Crocodile mouth”. The seismic exploration method was used to study the shell structure. It can improve quality of raw seismic data and image accurately with innovative applications of technology and methods. We analyzed the contact model between North China block and the Yangtze block by using new seismic data and other geophysical data. The aim of this paper is to analyze the collision evolution process of Yangtze block and North China block in the sea area, and the control function of evolution formation for foreland basin with the application of OBS sections, gravity inversion results and magnetic data. ©, 2015, Science Press. All right reserved.


Shang L.,Ocean University of China | Shang L.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Shang L.,Institute of Marine Geology | Zhang X.,Function Laboratory for Marine Mineral Resource Geology and Exploration | And 4 more authors.
Journal of Ocean University of China | Year: 2016

In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system: one data set was from the ‘Geological-geophysical map series of China Seas and adjacent areas’ database and the other was newly collected by R/V Kexue III in 2011. Magnetic and gravity data were reorganized and processed using the software MMDP, MGDP and RGIS. In addition to the description of the anomaly patterns in different areas, deep and shallow structure studies were performed by using several kinds of calculation, including a spectrum analysis, upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly. The depth of the Moho and magnetic basement were calculated. Based on the above work, several controversial tectonic problems were discussed. Compared to the shelf area and Ryukyu Arc, the Okinawa Trough has an obviously thinned crust, with the thinnest area having thickness less than 14 km in the southern part. The Taiwan-Sinzi belt, which terminates to the south by the NW-SE trending Miyako fault belt, contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough. As an important tectonic boundary, the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments. A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate. Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area. The gravity and magnetic data support the existence of a Great East China Sea, which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions, and might have extended southwestward and connected with the northern South China Sea shelf basin. © 2016, Science Press, Ocean University of China and Springer-Verlag Berlin Heidelberg.


Wang X.,CAS Qingdao Institute of Oceanology | Wang X.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Luan X.,CAS Qingdao Institute of Oceanology | Luan X.,Function Laboratory for Marine Mineral Resource Geology and Exploration
Geophysical Prospecting for Petroleum | Year: 2015

Q value extraction is easily affected by strong reflection amplitude caused by lithology, which causes multi-solutions for the calculation; thus, it is very difficult to distinguish the gas reservoir. Wavelet frequency division technology is a kind of interpretation method for seismic imaging based on spectrum analysis. The frequency division section includes different frequency components, and the processing of frequency division can avoid the mutual influence from different frequency components of seismic signals, also can treat the frequency information of the target reservoir with special means, which improves the stability of reservoir attributes extraction. Based on the above reasons, we firstly analyze the frequency interval of gas reservoir, and then use the wavelet frequency division technology to obtain the seismic data of this frequency interval. Based on the seismic data, the spectral ratio method in wavelet domain is applied to calculate the formation Q value. Model test and actual seismic data analysis shows that, the method has higher accuracy and applicability, which is more suitable for predicting gas reservoir. ©, 2015, Science Press. All right reserved.


Wu Z.-Q.,CAS Qingdao Institute of Oceanology | Wu Z.-Q.,Function laboratory for Marine Mineral Resource Geology and Exploration | Hao T.-Y.,CAS Institute of Geology and Geophysics | Tang S.-H.,First Marine Geological Party | And 8 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2016

The Bohai Sea is in the North China block and the South Yellow Sea is located in the Yangtze block. These seas are rich in oil and gas resources, related with block convergence and plate movement. The aim is to carry out seismic deep OBS detection in the Southern Yellow Sea and the Bohai Sea to get the seismic reflection and refraction information of lithosphere and the Moho surface for the study on the crust-mantle structure characteristics, the contact relation of the North China block and the Yangtze block and the tectonic effect of the plate movement and its control on the basin formation, evolution and hydrocarbon accumulation. The deep crust OBS exploration in the deep sea uses a conventional air-gun array which is made of several sub-arrays each containing a number of large volume air-guns. But in the shallow sea, it is difficult to play an effective role due to the gun depth limit and serious seafloor ghost reflection and source water ghost. To meet the needs for attenuation of water ghost reflection and enhancement of the low frequency content of seismic wavelet, based on the water depth condition and analysis of the principle of multi-level air-gun array and delay fired source applied in oil and gas exploration in the deep sea, we develop a method to delay the sub-array fired time for the tridimensional air-gun array source composed of a number of smaller volume air-guns. Compared with the multi-levels air-gun array, we apply a smaller depth difference and flexible sub-array sinking for sub air-gun array in order to adapt to the harsh environment for shooting the air-gun in the shallow water, thus we can get better effect for bubble suppression and ghost attenuation. A pattern of flexible delay fired time is designed for improving to output energy of the source and the quality of the wavelet. We design different combination schemes for tridimensional air-gun array and delay fired source and model its far-field wavelets. The amplitude-frequence distribution of our designed tridimensional air-gun array with delay fired source is more smooth than that of a conventional one, and more energy can be extended in the low frequency bands. Based on water depth conditions in the OBS exploration area, we applied respectively different tridimensional air-gun array and delay fired source pattern in the Bohai Sea and the Southern Yellow Sea. Compared with the deep crust OBS exploration using conventional large volume air-gun array in the Bohai Sea in 2012, the quality of the OBS data accquired by using new source is improved obviously, the seismic signal has a stronger amplitude, richer phase, higher resolution, better continuity and higher S/N ratio. The maximum propagation distance of source signal is over 150 km, which is more than that of the conventional large volume air-gun array. The deep crust OBS exploration which is the first one in the South Yellow Sea indicates the OBSs can record rich seismic phases including Ps, Pg, PmP and Pn both in the uplift areas where distributed the high velocity layers which had shielding effect on the seismic signals and the depression areas with large deposition thickness. The OBSs record quality is higher and the effective propagation distance of the air-gun signal is over 140 km.The deep crust OBS exploration test using tridimensional air-gun array with delay fired source technique shows that this method can generate seismic signals with long propagation distance and deep penetration in the shallow water, which can effectively suppress the source ghost effect and improve OBSs data quality. The method provides an ideal artificial source for marine seismic exploration, which can help study deep lithospheric structure, composition and status, and multichannel seismic detection for deep target layers. An important function for the tridimensional air-gun array and delay fired source technique is to attenuate the source ghost and to enhance low frequency energy. But the air-gun far field signals are also affected by the new design. Firstly, the source ghost is an effective attenuator of bubble pulses, the tridimensional air-gun array and delay fired source technique deliver a lower peak-to-bubble ratio (PTB) than a conventional air-gun array. Secondly, since the guns are towed deeper, they fire under higher hydrostatic pressure, which would reduce bubble sizes and oscillation periods and result in decrease of the high frequency contents. Thirdly, the difference of the bubble sizes caused by different array depths leads to less flexibility in array design and bubble pulse attenuation. Therefore, the far field wavelet modeling is the key to ensure an effective tridimensional air-gun array with delay fired source design. To avoid the side effects, we must carefully carry out the simulation and analysis of far-field wavelets to develop an optimal design for tridimensional air-gun array and delay fired source. © 2016, Science Press. All right reserved.


Zhang X.-H.,CAS Qingdao Institute of Oceanology | Zhang X.-H.,Function Laboratory for Marine Mineral Resource Geology and Exploration | Yang J.-Y.,CAS Qingdao Institute of Oceanology | Li G.,CAS Qingdao Institute of Oceanology | Yang Y.-Q.,CAS Qingdao Institute of Oceanology
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

The South Yellow Sea basin is a large superposed basin composed of a Paleozoic-Mesozoic marine sedimentary basin and Mesozoic-Cenozoic terringenous sedimentary basin. The structure and stratigraphic distribution of the lower crystal basement and the upper folded basement of the two kinds of basins are discussed based on integrated geological and geophysical data. New seismic data interpretation combined with drilling data and geological correlation between land and sea are used to identify the marine Paleozoic-Mesozoic stratigraphic sequence. The depth of the top surface of the marine Paleozoic-Mesozoic strata is determined by seismic interpretation; undulation of the bottom surface is derived by magnetic inversion. The residual thickness of Triassic Qinglong limestone and upper Permian strata is also analyzed in order to understand the distribution and structure features of the marine Paleozoic-Mesozoic strata. The thickness and distribution of the marine sequence are mainly controlled by the undulation of the basement, and also influenced greatly by the Indosinian movement. The thickness of the marine Paleozoic-Mesozoic strata is comparatively stable in the central uplift. The lower Triassic Qinglong formation and the upper Permian Dalong and Longtan formations are widely distributed in the southern depression and the Wunansha uplift of the South Yellow Sea basin, while the distribution of this sequence in the northern depression is very limited; in the central uplift, few are left due to uplift and denudation. At present, the residual thickness of the lower Paleozoic remains unknown due to limited data. ©, 2014, Science Press. All right reserved.

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