More than 20000 dayside auroral arcs of the 557.7 and 630.0 nm emission intensities have been statistically studied, and the dependences of the I557.7/I630.0 ratio on the I557.7 emission intensity have been determined. The 557.7 nm emission intensity has two maximum values in the hot spot and warm spot regions, with average values of 2.2 and 2.9 kR, respectively. But there is a maximum near magnetic noon for 630.0 nm emission intensity, with an average value of 1.5 kR. In the I557.7 emission range 0.1~10 kR, the I557.7/I630.0 ratio tends to increase from 0.2 to 9. The correlation between emission intensity and precipitating electron spectra has been investigated using 17 cases of DMSP passing through 40 auroral arcs above Chinese Arctic Yellow River Station (YRS). We obtain the equations that the average energy of the electrons is proportional to the I557.7/I630.0 ratio. There is a positive correlation between the total energy flux of the electrons and the I557.7 emission intensity. The typical region of electron precipitation, where the auroral arcs were observed, was the boundary plasma sheet (BPS) in the prenoon and postnoon sectors. We also found some low-energy precipitating electrons from the region of mantle, where the arcs are located poleward of dayside auroral oval. The magnetic source region of the precipitating electrons with low energy was identified as the low latitude boundary layer (LLBL) adjacent to magnetic noon. Arcs are located in the lower latitude in this region.
{"title":"CORRELATION BETWEEN EMISSION INTENSITIES IN DAYSIDE AURORAL ARCS AND PRECIPITATING ELECTRON SPECTRA","authors":"Qiu Qi, Y. Huigen, Lu Quan-Ming, Huang Ze-jun","doi":"10.1002/CJG2.30023","DOIUrl":"https://doi.org/10.1002/CJG2.30023","url":null,"abstract":"More than 20000 dayside auroral arcs of the 557.7 and 630.0 nm emission intensities have been statistically studied, and the dependences of the I557.7/I630.0 ratio on the I557.7 emission intensity have been determined. The 557.7 nm emission intensity has two maximum values in the hot spot and warm spot regions, with average values of 2.2 and 2.9 kR, respectively. But there is a maximum near magnetic noon for 630.0 nm emission intensity, with an average value of 1.5 kR. In the I557.7 emission range 0.1~10 kR, the I557.7/I630.0 ratio tends to increase from 0.2 to 9. The correlation between emission intensity and precipitating electron spectra has been investigated using 17 cases of DMSP passing through 40 auroral arcs above Chinese Arctic Yellow River Station (YRS). We obtain the equations that the average energy of the electrons is proportional to the I557.7/I630.0 ratio. There is a positive correlation between the total energy flux of the electrons and the I557.7 emission intensity. The typical region of electron precipitation, where the auroral arcs were observed, was the boundary plasma sheet (BPS) in the prenoon and postnoon sectors. We also found some low-energy precipitating electrons from the region of mantle, where the arcs are located poleward of dayside auroral oval. The magnetic source region of the precipitating electrons with low energy was identified as the low latitude boundary layer (LLBL) adjacent to magnetic noon. Arcs are located in the lower latitude in this region.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30023","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51231391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To study the electromagnetic (EM) diffusion of a time-domain airborne electromagnetic (AEM) system, we first calculate the frequency-domain EM field inside the earth based on the continuity boundary condition and then transform it into time-domain via a Fourier transform. We calculate the EM fields induced by a step pulse for a homogeneous half-space and a two-layer earth model and display the EM diffusion in the earth as 2D vectors or 3D animated time-varying contours (like the “smoke ring”). These time-domain current rings display the true EM diffusion, because they demonstrate the spatial variation and decay of underground EM fields with time. The study of the EM current rings shows that the EM diffusion is strongly influenced by the resistivity structure inside the earth. In a conductive earth, the current ring diffuses slowly but decays fast, while in a resistive earth it diffuses fast but decays slowly. The induced current for a vertical magnetic dipole forms a single current ring that propagates with time outward and downward, while for a horizontal magnetic dipole, the induced current forms two stacked current rings in the underground, diffusing with time into the deep earth. Based on the EM current ring, we find that the imaging depth for AEM data is about 0.55 times the EM diffusion depth. By showing the underground induced current as vectors and 3D time-varying animated contours, the EM diffusion and smoke ring are clearly observed. An animated EM smoke ring offers more information than a static contour of current density. The relation between imaging depth and diffusion depth is further confirmed by the smoke rings. Study on EM smoke ring can not only offer an insight into EM diffusion in the earth, but can also assist in airborne EM data interpretation.
{"title":"TIME‐DOMAIN ELECTROMAGNETIC DIFFUSION AND IMAGING DEPTH FOR AIRBORNE ELECTROMAGNETIC DATA","authors":"Yin Chang-chun, Qiu Changkai, L. Yunhe, Cai Jing","doi":"10.1002/CJG2.30025","DOIUrl":"https://doi.org/10.1002/CJG2.30025","url":null,"abstract":"To study the electromagnetic (EM) diffusion of a time-domain airborne electromagnetic (AEM) system, we first calculate the frequency-domain EM field inside the earth based on the continuity boundary condition and then transform it into time-domain via a Fourier transform. We calculate the EM fields induced by a step pulse for a homogeneous half-space and a two-layer earth model and display the EM diffusion in the earth as 2D vectors or 3D animated time-varying contours (like the “smoke ring”). These time-domain current rings display the true EM diffusion, because they demonstrate the spatial variation and decay of underground EM fields with time. The study of the EM current rings shows that the EM diffusion is strongly influenced by the resistivity structure inside the earth. In a conductive earth, the current ring diffuses slowly but decays fast, while in a resistive earth it diffuses fast but decays slowly. The induced current for a vertical magnetic dipole forms a single current ring that propagates with time outward and downward, while for a horizontal magnetic dipole, the induced current forms two stacked current rings in the underground, diffusing with time into the deep earth. Based on the EM current ring, we find that the imaging depth for AEM data is about 0.55 times the EM diffusion depth. By showing the underground induced current as vectors and 3D time-varying animated contours, the EM diffusion and smoke ring are clearly observed. An animated EM smoke ring offers more information than a static contour of current density. The relation between imaging depth and diffusion depth is further confirmed by the smoke rings. Study on EM smoke ring can not only offer an insight into EM diffusion in the earth, but can also assist in airborne EM data interpretation.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30025","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51231544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
According to the ultrasonic data of 51 measured core samples from 17 wells in the Sulige gas field, 304 groups of elastic parameters data including VP/VS and Poisson's ratio are obtained corresponding to different porosities and water saturations. The optimized rock physics corrections among the bulk modulus, Poisson's ratio, and gas saturation indicate that the Brie model (e=2) can fairly characterize the properties of upper Paleozoic Permian H8 reservoir in the Sulige gas field. Therefore, the proposed rock physics is able to estimate the physical parameters variation of tight sandstone reservoirs with gas-bearing saturation level. The proposed rock physics model is applied to predict gas-water reservoir by utilizing multi-wave seismic data of the Sulige gas field. The field test indicates that this model is capable of characterizing attributes of the target zone and predicting the gas-bearing reservoir.
{"title":"A STUDY ON THE ROCK PHYSICS MODEL OF GAS RESERVOIR IN TIGHT SANDSTONE","authors":"Wang Da-xing","doi":"10.1002/CJG2.30028","DOIUrl":"https://doi.org/10.1002/CJG2.30028","url":null,"abstract":"According to the ultrasonic data of 51 measured core samples from 17 wells in the Sulige gas field, 304 groups of elastic parameters data including VP/VS and Poisson's ratio are obtained corresponding to different porosities and water saturations. The optimized rock physics corrections among the bulk modulus, Poisson's ratio, and gas saturation indicate that the Brie model (e=2) can fairly characterize the properties of upper Paleozoic Permian H8 reservoir in the Sulige gas field. Therefore, the proposed rock physics is able to estimate the physical parameters variation of tight sandstone reservoirs with gas-bearing saturation level. The proposed rock physics model is applied to predict gas-water reservoir by utilizing multi-wave seismic data of the Sulige gas field. The field test indicates that this model is capable of characterizing attributes of the target zone and predicting the gas-bearing reservoir.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30028","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wang Qiao, Wang Xu-ben, Yang Jian, Minseok Gang, Guo Jing
Skarn deposit is one of the main gold-polymetallic deposits in Beiya, Yunnan, and constrained by its porphyries, structures and stratums, the favorable ore-prospecting spaces are contact zones between intermediateacid rocks and carbonatite. Based on the physical characteristics of rocks, we realized the transition between target geological body and the geophysical field and extracted the useful information. Skarn iron deposits are characterized by low-medium resistivity in contact zone, low density of porphyries, high susceptibility and high polarizability of the iron ore. Utilizing the geological and geophysical information, we analyzed ore-controlling factors in different stages, implemented the locating of concealed skarn iron deposits, established a geophysical exploration mode, verified the validity of the study method on the periphery of the ore district and obtained favorable exploration results. We also proposed a locating and predicting method for the concealed skarn iron deposits, which is applicable to Beiya and other similar ore-forming geological conditions.
{"title":"LOCATING OF CONCEALED SKARN IRON ORE DEPOSIT BASED ON MULTIVARIATE INFORMATION CONSTRAINTS: A CASE STUDY OF BEIYA GOLD MINE IN YUNNAN PROVINCE","authors":"Wang Qiao, Wang Xu-ben, Yang Jian, Minseok Gang, Guo Jing","doi":"10.1002/CJG2.30029","DOIUrl":"https://doi.org/10.1002/CJG2.30029","url":null,"abstract":"Skarn deposit is one of the main gold-polymetallic deposits in Beiya, Yunnan, and constrained by its porphyries, structures and stratums, the favorable ore-prospecting spaces are contact zones between intermediateacid rocks and carbonatite. Based on the physical characteristics of rocks, we realized the transition between target geological body and the geophysical field and extracted the useful information. Skarn iron deposits are characterized by low-medium resistivity in contact zone, low density of porphyries, high susceptibility and high polarizability of the iron ore. Utilizing the geological and geophysical information, we analyzed ore-controlling factors in different stages, implemented the locating of concealed skarn iron deposits, established a geophysical exploration mode, verified the validity of the study method on the periphery of the ore district and obtained favorable exploration results. We also proposed a locating and predicting method for the concealed skarn iron deposits, which is applicable to Beiya and other similar ore-forming geological conditions.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30029","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232146","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Crustal anisotropy at multiple depths is essential for studying the vertical variation of crustal deformation. Due to the complexity of the crust, mapping the crustal anisotropy at different depth from teleseismic receiver function (RF) is an ongoing subject that requires further studies. Based on the previous works, this paper goes further to discuss the RF wavefield pattern of stratified crustal anisotropy by means of the generalized reflection and transmission coefficients method, which provides us a new theoretical basis for understanding the RF data with stratified anisotropic crustal models. In addition, we develop a global inversion method for extracting stratified anisotropic models based on the particle swarm algorithm. The test results from both numerical and real data show that, our method can correctly recover the depth-dependent anisotropic parameters from the RF data and distinguish different anisotropic layers of the crust, as long as isotropic velocity model is well determined. Noise suppression in data processing via curvelet transform is useful for the analysis of crustal anisotropy.
{"title":"STRATIFIED CRUSTAL ANISOTROPY FROM RECEIVER FUNCTION AND ITS PARTICLE SWARM INVERSION","authors":"Qi Shao-hua, L. Qi-yuan, Chen Jiu-hui, Guo Biao","doi":"10.1002/CJG2.30027","DOIUrl":"https://doi.org/10.1002/CJG2.30027","url":null,"abstract":"Crustal anisotropy at multiple depths is essential for studying the vertical variation of crustal deformation. Due to the complexity of the crust, mapping the crustal anisotropy at different depth from teleseismic receiver function (RF) is an ongoing subject that requires further studies. Based on the previous works, this paper goes further to discuss the RF wavefield pattern of stratified crustal anisotropy by means of the generalized reflection and transmission coefficients method, which provides us a new theoretical basis for understanding the RF data with stratified anisotropic crustal models. In addition, we develop a global inversion method for extracting stratified anisotropic models based on the particle swarm algorithm. The test results from both numerical and real data show that, our method can correctly recover the depth-dependent anisotropic parameters from the RF data and distinguish different anisotropic layers of the crust, as long as isotropic velocity model is well determined. Noise suppression in data processing via curvelet transform is useful for the analysis of crustal anisotropy.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30027","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Following the magnetotelluric method, the apparent resistivity of the controlled source audio-frequency magnetotelluric method is usually derived from the ratio of electric field and magnetic field. For CSAMT, as the source power current density is known, both of the electric and magnetic field components are related to the resistivity of the earth. The apparent resistivity can be obtained from the single electric field or magnetic field. In this paper, we put forward the inversion and interpretation methods for component data of CSAMT after analyzing the data features. During the curve fitting inversion, in order to deduct real formation and obtain finer resistivity-depth section, the number of frequency of curves is regarded as the inversion earth layers number. The all-zone electric component apparent resistivity inversion is developed. Then, the phase is introduced into the inversion process to cancel the static offset. The prospecting for water-filled goaf in Shanxi Province suggests that the single component interpretation is useful.
{"title":"INTERPRETATION OF CSAMT SINGLE-COMPONENT DATA","authors":"Yan Shu, Xue Guo-qiang, Qiu Weizhong, Zhou Nannan","doi":"10.1002/CJG2.30030","DOIUrl":"https://doi.org/10.1002/CJG2.30030","url":null,"abstract":"Following the magnetotelluric method, the apparent resistivity of the controlled source audio-frequency magnetotelluric method is usually derived from the ratio of electric field and magnetic field. For CSAMT, as the source power current density is known, both of the electric and magnetic field components are related to the resistivity of the earth. The apparent resistivity can be obtained from the single electric field or magnetic field. In this paper, we put forward the inversion and interpretation methods for component data of CSAMT after analyzing the data features. During the curve fitting inversion, in order to deduct real formation and obtain finer resistivity-depth section, the number of frequency of curves is regarded as the inversion earth layers number. The all-zone electric component apparent resistivity inversion is developed. Then, the phase is introduced into the inversion process to cancel the static offset. The prospecting for water-filled goaf in Shanxi Province suggests that the single component interpretation is useful.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30030","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For detecting, controlling and monitoring the coalfield fire area, we deeply integrated Internet innovative achievement into traditional geological exploration technology, and developed a permanent wireless sensor network remote monitoring system with the functions of detecting the range and central temperature of fire area, continuous collection, high temperature detection, remote control, etc. The new sensor node, which can be connected with pole-dipole device, was designed and deployed in the underground fire zone roadway for monitoring. The solar power supply device with protective circuit supplied continuous enough energy to on-site data collection network. The data was transmitted to monitoring center through the mobile connection network and Internet for remote control and monitoring. The developed monitoring system that was deployed simultaneously in 12 fire areas of Xinjiang has been working for 45 months, which means technical measures can guarantee long-term stability maintenance free operation of the monitoring system. Urumqi monitoring center has received more than 1.1 million field data that can be preserved permanently and queried freely after authorization. This information provided basic data for the management of large area of coal spontaneous combustion fire area in Xinjiang. The results show that fully utilizing the Internet for optimization and integration in geophysical exploration and monitoring has the vital significance to promote coal geological exploration innovation and production capacity.
{"title":"HIGH RESOLUTION RESISTIVITY DETECTING AND REMOTE INTERNET MONITORING OF COALFIELD FIRE","authors":"Cao Qinghua, Yan Shu, Xue Guo-qiang, Zhu Na","doi":"10.1002/CJG2.30031","DOIUrl":"https://doi.org/10.1002/CJG2.30031","url":null,"abstract":"For detecting, controlling and monitoring the coalfield fire area, we deeply integrated Internet innovative achievement into traditional geological exploration technology, and developed a permanent wireless sensor network remote monitoring system with the functions of detecting the range and central temperature of fire area, continuous collection, high temperature detection, remote control, etc. The new sensor node, which can be connected with pole-dipole device, was designed and deployed in the underground fire zone roadway for monitoring. The solar power supply device with protective circuit supplied continuous enough energy to on-site data collection network. The data was transmitted to monitoring center through the mobile connection network and Internet for remote control and monitoring. The developed monitoring system that was deployed simultaneously in 12 fire areas of Xinjiang has been working for 45 months, which means technical measures can guarantee long-term stability maintenance free operation of the monitoring system. Urumqi monitoring center has received more than 1.1 million field data that can be preserved permanently and queried freely after authorization. This information provided basic data for the management of large area of coal spontaneous combustion fire area in Xinjiang. The results show that fully utilizing the Internet for optimization and integration in geophysical exploration and monitoring has the vital significance to promote coal geological exploration innovation and production capacity.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30031","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Based on a viscous-elastic crustal model with constraint conditions from GPS and seismic dislocation data and adopting the finite element method, we analyzed the crustal deformation characteristics caused by 2001 Kunlun Mountain M S 8.1, 2008 Wenchuan M S 8.0 and 2015 Nepal M S 8.1 earthquakes, obtained the displacement and deformation field. These earthquakes have occurred in the north, east, and south margins of the Tibetan Plateau respectively. Our primary results suggest obvious differences in deformation regimes, seismogenic fault geometry and source parameters, as well as crustal deformation patters despite the substantially similar magnitudes. These differences caused by seismogenic fault nature and subsurface structures are mainly manifested by different scopes of deformed regions and different strain amplitudes. Through these simulation results, we can detect more about the distribution characteristics of stress loading and unloading area caused by large earthquakes. Moreover, it plays an important role in forecasting the earthquake possibility of seismogenic region.
{"title":"THE DISTRIBUTION CHARACTERISTICS OF DEFORMATION FIELD CAUSED BY THREE GREAT EARTHQUAKES IN THE QINGHAI-TIBET PLATEAU AND ITS VICINITY SINCE 2001","authors":"Zhang Yuan-sheng, Zheng Xiao-jing, W. Lanmin","doi":"10.1002/CJG2.30026","DOIUrl":"https://doi.org/10.1002/CJG2.30026","url":null,"abstract":"Based on a viscous-elastic crustal model with constraint conditions from GPS and seismic dislocation data and adopting the finite element method, we analyzed the crustal deformation characteristics caused by 2001 Kunlun Mountain M S 8.1, 2008 Wenchuan M S 8.0 and 2015 Nepal M S 8.1 earthquakes, obtained the displacement and deformation field. These earthquakes have occurred in the north, east, and south margins of the Tibetan Plateau respectively. Our primary results suggest obvious differences in deformation regimes, seismogenic fault geometry and source parameters, as well as crustal deformation patters despite the substantially similar magnitudes. These differences caused by seismogenic fault nature and subsurface structures are mainly manifested by different scopes of deformed regions and different strain amplitudes. Through these simulation results, we can detect more about the distribution characteristics of stress loading and unloading area caused by large earthquakes. Moreover, it plays an important role in forecasting the earthquake possibility of seismogenic region.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30026","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51231630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chen Jiangxin, Song Hai-bin, Guan Yongxian, Yang Sheng-xiong, Bai Yang, Geng Ming‐Hui
Submarine cold seeps are widely distributed in the continental margin seas around the world. In this study, we apply a conventional multichannel seismic reflection (seismic oceanography) method to image the water column near the seafloor in order to detect cold seeps. In addition to analyzing the fluid escape structures, we also describe and discuss the development positions, seismic reflection characteristics as well as features of the cold seeps. The seismic reflection from the water column is very weak; therefore, the seismic sections above and below the seafloor are processed in two different sequences as follows:(1) geometry definition, direct wave attenuation and amplitude recovery, high-pass filter, common midpoint sorting, constant velocity (seawater sound velocity) stack, and post-stack FK filter in some sections; and (2) data quality control, amplitude recovery, 6~100 Hz bandpass filter, multiple attenuation, deconvolution, velocity analysis, normal move-out correction, common midpoint stack, post-stack noise attenuation, 4~70 Hz bandpass filter, and FX migration. The processed sections are then assembled together along the seafloor after carefully adjusting the color scale. The analysis shows that active cold seeps primarily present plume, broom, and/or irregular shapes that have weak and chaotic seismic reflections in the water column. The seismic reflection amplitude is enhanced at times; this could be attributed to the suspension of mud or particles in the water column. Cold seepage activities are typically associated with fluid escape structures, including mud diapirs, pipes, faults, fractures, gas chimneys, seabed pockmarks, and mud volcanoes. This indicates fluid migration from deep to shallow strata, fluid seepage or escape at the seafloor, as well as the formation of widespread cold seep activities. All the results herein are derived from a comprehensive interpretation of the seismic sections of the water columns and strata; however, further field studies, theoretical simulations, and experiments are required to confirm these conclusions.
{"title":"A PRELIMINARY STUDY OF SUBMARINE COLD SEEPS BY SEISMIC OCEANOGRAPHY TECHNIQUES","authors":"Chen Jiangxin, Song Hai-bin, Guan Yongxian, Yang Sheng-xiong, Bai Yang, Geng Ming‐Hui","doi":"10.1002/CJG2.30032","DOIUrl":"https://doi.org/10.1002/CJG2.30032","url":null,"abstract":"Submarine cold seeps are widely distributed in the continental margin seas around the world. In this study, we apply a conventional multichannel seismic reflection (seismic oceanography) method to image the water column near the seafloor in order to detect cold seeps. In addition to analyzing the fluid escape structures, we also describe and discuss the development positions, seismic reflection characteristics as well as features of the cold seeps. The seismic reflection from the water column is very weak; therefore, the seismic sections above and below the seafloor are processed in two different sequences as follows:(1) geometry definition, direct wave attenuation and amplitude recovery, high-pass filter, common midpoint sorting, constant velocity (seawater sound velocity) stack, and post-stack FK filter in some sections; and (2) data quality control, amplitude recovery, 6~100 Hz bandpass filter, multiple attenuation, deconvolution, velocity analysis, normal move-out correction, common midpoint stack, post-stack noise attenuation, 4~70 Hz bandpass filter, and FX migration. The processed sections are then assembled together along the seafloor after carefully adjusting the color scale. The analysis shows that active cold seeps primarily present plume, broom, and/or irregular shapes that have weak and chaotic seismic reflections in the water column. The seismic reflection amplitude is enhanced at times; this could be attributed to the suspension of mud or particles in the water column. Cold seepage activities are typically associated with fluid escape structures, including mud diapirs, pipes, faults, fractures, gas chimneys, seabed pockmarks, and mud volcanoes. This indicates fluid migration from deep to shallow strata, fluid seepage or escape at the seafloor, as well as the formation of widespread cold seep activities. All the results herein are derived from a comprehensive interpretation of the seismic sections of the water columns and strata; however, further field studies, theoretical simulations, and experiments are required to confirm these conclusions.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.30032","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51232487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ma Qin-zhong, Qian Jia-dong, Li Wei, Zhao Wenzhou, Fang Guoqing
The relation between the flowing characteristics of electric current and the geological structure is one of very important issues in the study of geoelectric field in seismo-electromagnetics. This paper deals with heavy currents from four different sources injected into the underground and their consequences in the observations from the network of geoelectric field stations associated with the currents, which provides us with a good opportunity to study the issues. The sources are the earth electrodes of some substations of HVDC transmission line systems in East-south China around Shanghai area (Huadong area) with the currents of 1200 to 4780A injected. The recordings of the additional signals of geoelectric field corresponding to the currents have been collected at eight geoelectric field stations in the same area. The following features could be seen in the study. ① Some stations show the selectivity effect. The magnitude of the additional geoelectric field recorded at different stations varied from one source to another, for example Pudong station is near all the heavy current sources, but only the clear signals originated from Nanqiao earth electrode were recorded while no signals from other sources (Tongli, Huaxin, and Fengxian), which shows so-called selectivity effect of the site; ② Station-source distance effect. The maximum observation distance is 350 km, beyond that no additional geoelectric signals from the sources could be recorded; ③ The source azimuth determination has complicated characteristics. For example, at Chongming station the errors are minimum, only 0.2° and 0.8°, respectively, between the actual and calculated source azimuths determined by the signals from Tongli and Xinhua earth electrodes. However, Qingpu station is the nearest station from the heavy current sources, these errors are larger than that obtained from Chongming station due to some unknown reasons; ④ The effect of non-uniformity of the geoelectric field. At the stations in the studied area, the ratios of signals from long dipole over that of short dipoles do not follow the regular patterns which appear in the cases of homogeneous medium structure underneath the observation stations, which illustrates a kind of non-uniformity effect, which is discussed in detail in this paper and proved by the results from a 2-D high density geoelectrical prospecting in the studied area. ⑤ The peculiar reverse effect of polarization direction. For the additional geoelectric field signals recorded at Qingpu and Chongming stations the polarization directions on the long diploes and short diploes are reverse, which need to be further studied in the future to explain the phenomenon. The influence of the three factors, i.e., the configuration of a point source and the electrode distribution of station, the heterogeneity of medium in a large area, as well as the fine structure of the underground medium at a station, is discussed in this paper which might give a relatively clear exp
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