Major and/or great earthquakes frequently occured in western China, where exist many striking seismotectonic zones such as Tian Shan, Altay, Pamir and Kunlun Mountains. This paper analyzes the characteristics of the gravity field in western China, inverts the depth of Moho interface by the Parker-Oldenburg method with gravity data and seismic profiles. Through comparison with the results of seismic tomography inversion, we analyze crustal structure of the study area. The results show that the study area is significantly heterogeneous in crustal structure, with main orogenic belts of high-speed while basins and major depressions of low speed. The orogenic belts in the study area are generally Moho depression areas while the basins are the Moho uplift areas. According to the calculation results and epicenter distribution of the study area, we discuss the correlation between crustal structure and major earthquakes. The earthquakes in this region are closely related to crustal heterogeneity, which mainly happen around the crustal velocity change belts and in the regions with great crustal velocity differences. Under the effect of tectonic stress, these crustal non-uniform areas are prone to major earthquakes, which is one of the tectonic reasons for high seismicity in orogenic belts and near the boundary between basins and mountains in western China.
{"title":"Characteristics of Crustal Structure and Their Relation with Major Earthquakes in Western China","authors":"Jiang Di-Di, Jiang Wei-wei, Xu Yi, Hao Tian-yao, Huang Weijian, Yu Jing-feng","doi":"10.1002/CJG2.20157","DOIUrl":"https://doi.org/10.1002/CJG2.20157","url":null,"abstract":"Major and/or great earthquakes frequently occured in western China, where exist many striking seismotectonic zones such as Tian Shan, Altay, Pamir and Kunlun Mountains. This paper analyzes the characteristics of the gravity field in western China, inverts the depth of Moho interface by the Parker-Oldenburg method with gravity data and seismic profiles. Through comparison with the results of seismic tomography inversion, we analyze crustal structure of the study area. The results show that the study area is significantly heterogeneous in crustal structure, with main orogenic belts of high-speed while basins and major depressions of low speed. The orogenic belts in the study area are generally Moho depression areas while the basins are the Moho uplift areas. According to the calculation results and epicenter distribution of the study area, we discuss the correlation between crustal structure and major earthquakes. The earthquakes in this region are closely related to crustal heterogeneity, which mainly happen around the crustal velocity change belts and in the regions with great crustal velocity differences. Under the effect of tectonic stress, these crustal non-uniform areas are prone to major earthquakes, which is one of the tectonic reasons for high seismicity in orogenic belts and near the boundary between basins and mountains in western China.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20157","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220564","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}
The South Yellow Sea basin is a large superposed basin composed of a Paleozoic-Mesozoic marine sedimentary basin and Mesozoic-Cenozoic terrigenous sedimentary basin. This work studied the structure and stratigraphic distribution of the lower crystal basement and the upper folded basement of the two kinds of basins 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 the Triassic Qinglong limestone and the upper Permian strata is also analyzed 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 succession in the northern depression is very limited; in the central uplift, little is are left due to uplift and denudation. At present, the residual thickness of the lower Paleozoic remains unknown due to limited data available.
{"title":"Basement Structure and Distribution of Mesozoic‐Paleozoic Marine Strata in the South Yellow Sea Basin","authors":"Zhang Xun-hua, Yang Jin-yu, L. Gang, Yan Yanqiu","doi":"10.1002/CJG2.20158","DOIUrl":"https://doi.org/10.1002/CJG2.20158","url":null,"abstract":"The South Yellow Sea basin is a large superposed basin composed of a Paleozoic-Mesozoic marine sedimentary basin and Mesozoic-Cenozoic terrigenous sedimentary basin. This work studied the structure and stratigraphic distribution of the lower crystal basement and the upper folded basement of the two kinds of basins 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 the Triassic Qinglong limestone and the upper Permian strata is also analyzed 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 succession in the northern depression is very limited; in the central uplift, little is are left due to uplift and denudation. At present, the residual thickness of the lower Paleozoic remains unknown due to limited data available.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20158","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220590","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 Wei-guo, Yang Fang-yuan, Wang Hao-yue, Y. Tao, Y. Ke, LI Shu-kun, Fan Wen-Xuan
The spatial-temporal distribution characters of trace gases in the stratosphere and troposphere are affected by the Brewer-Dobson (BD) circulation. Understanding the distribution characters of the BD circulation is very important for further studying the influence of stratosphere and troposphere exchange and forecasting the global climate change. The BD circulation is described as the Lagrangian-mean circulation, which is difficult to diagnose directly from meteorological observations. The methods of the transformed Eulerian-mean (TEM) equations and integrating residual meridional velocity in the vertical were used to analyze the spatial-temporal distribution characters of the BD circulation based on the ERA-Interim reanalysis data at 12:00 UTC for 1979–2011. We further compared the distribution characters of BD circulation with the result calculated by the method of DC (Downward Control) principle and studied the relationship between the stratospheric zonal mean temperature and BD circulation. The BD circulation was calculated using ERA-Interim reanalysis data for 1979–2011 by integrating residual meridional velocity in the vertical direction. The results show that the ascending centers of BD circulation varied with seasons. It ascended at 30°S in the stratosphere from December to February (DJF), while from June to August (JJA) it ascended between 25°N and 30°N. The circulation pattern in the winter hemisphere was stronger than the summer hemisphere. In March to May (MAM) and September to November (SON), the ascending centers were between equator to 5°N, and circulation were relatively symmetric between the two hemispheres. The maximum mass flux in the tropical and extratropical northern hemisphere appeared during DJF, and the minimum appeared during JJA. The mass flux in the extratropical southern hemisphere was just the opposite. Mass flux across the 100 hPa and 50 hPa pressure surface in the tropical and extratropical areas tended to decrease, and also varied obviously with the changing of season. The long-term trend of stratospheric zonal mean temperature was consistent with the long-term weakening trend of BD circulation, which indicates that the global BD circulation has been weakened. Meanwhile, the zonal mean temperature at different altitudes and latitudes varied with seasons. From the perspective of the global mass transportation, the stratospheric BD circulation has been weakened in the past 33 years, especially in the middle and lower stratosphere, which was consistent with the long-term trend of temperature. This weakened trend was consistent with the observations of stratospheric air and other model results. But the method of DC principle, GCMs model and other studies show that the stratospheric BD circulation has been enhanced in the past years. Using different methods and data would make the trend estimation of BD circulation unreliable. Therefore, further research is required to improve this estimation.
{"title":"The Distribution Characters of the Stratospheric Brewer‐Dobson Circulation Inferred from Era‐Interim","authors":"Wang Wei-guo, Yang Fang-yuan, Wang Hao-yue, Y. Tao, Y. Ke, LI Shu-kun, Fan Wen-Xuan","doi":"10.1002/CJG2.20152","DOIUrl":"https://doi.org/10.1002/CJG2.20152","url":null,"abstract":"The spatial-temporal distribution characters of trace gases in the stratosphere and troposphere are affected by the Brewer-Dobson (BD) circulation. Understanding the distribution characters of the BD circulation is very important for further studying the influence of stratosphere and troposphere exchange and forecasting the global climate change. The BD circulation is described as the Lagrangian-mean circulation, which is difficult to diagnose directly from meteorological observations. The methods of the transformed Eulerian-mean (TEM) equations and integrating residual meridional velocity in the vertical were used to analyze the spatial-temporal distribution characters of the BD circulation based on the ERA-Interim reanalysis data at 12:00 UTC for 1979–2011. We further compared the distribution characters of BD circulation with the result calculated by the method of DC (Downward Control) principle and studied the relationship between the stratospheric zonal mean temperature and BD circulation. The BD circulation was calculated using ERA-Interim reanalysis data for 1979–2011 by integrating residual meridional velocity in the vertical direction. The results show that the ascending centers of BD circulation varied with seasons. It ascended at 30°S in the stratosphere from December to February (DJF), while from June to August (JJA) it ascended between 25°N and 30°N. The circulation pattern in the winter hemisphere was stronger than the summer hemisphere. In March to May (MAM) and September to November (SON), the ascending centers were between equator to 5°N, and circulation were relatively symmetric between the two hemispheres. The maximum mass flux in the tropical and extratropical northern hemisphere appeared during DJF, and the minimum appeared during JJA. The mass flux in the extratropical southern hemisphere was just the opposite. Mass flux across the 100 hPa and 50 hPa pressure surface in the tropical and extratropical areas tended to decrease, and also varied obviously with the changing of season. The long-term trend of stratospheric zonal mean temperature was consistent with the long-term weakening trend of BD circulation, which indicates that the global BD circulation has been weakened. Meanwhile, the zonal mean temperature at different altitudes and latitudes varied with seasons. From the perspective of the global mass transportation, the stratospheric BD circulation has been weakened in the past 33 years, especially in the middle and lower stratosphere, which was consistent with the long-term trend of temperature. This weakened trend was consistent with the observations of stratospheric air and other model results. But the method of DC principle, GCMs model and other studies show that the stratospheric BD circulation has been enhanced in the past years. Using different methods and data would make the trend estimation of BD circulation unreliable. Therefore, further research is required to improve this estimation.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20152","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220380","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}
Yang Wen-cai, Sun Yan-yun, Hou Zunze, Yuan Chang-qing
This paper presents new systematic methods of regional gravity data processing that combine theories based on multi-scale wavelet analysis, spectral analysis of potential fields, geophysical inversion, and information extraction. We call this data processing system as the multi-scale scratch analysis for delineation of crustal structures, deformation belts and division of continental tectonic units. The multi-scale scratch analysis contains four modules; they are spectral analysis for division of density layers, decomposition of the field by using wavelet transformation and multi-scale analysis, depth estimation and density inversion of decomposed gravity anomalies, and scratch analysis. The basic principles, application techniques and examples for each module are explained. As a complicated and sophisticated process, the multi-discipline research on regional geophysics from geophysical investigation to tectonic results requires combination of new methods and techniques coming from different disciplines, to build a wide and thick theoretic base for supporting the multi-discipline research. The multi-scale scratch analysis combines supporting bases coming from applied mathematics, geophysics, and information science respectively.
{"title":"A Multi‐Scale Scratch Analysis Method for Quantitative Interpretation of Regional Gravity Fields","authors":"Yang Wen-cai, Sun Yan-yun, Hou Zunze, Yuan Chang-qing","doi":"10.1002/CJG2.20154","DOIUrl":"https://doi.org/10.1002/CJG2.20154","url":null,"abstract":"This paper presents new systematic methods of regional gravity data processing that combine theories based on multi-scale wavelet analysis, spectral analysis of potential fields, geophysical inversion, and information extraction. We call this data processing system as the multi-scale scratch analysis for delineation of crustal structures, deformation belts and division of continental tectonic units. The multi-scale scratch analysis contains four modules; they are spectral analysis for division of density layers, decomposition of the field by using wavelet transformation and multi-scale analysis, depth estimation and density inversion of decomposed gravity anomalies, and scratch analysis. The basic principles, application techniques and examples for each module are explained. As a complicated and sophisticated process, the multi-discipline research on regional geophysics from geophysical investigation to tectonic results requires combination of new methods and techniques coming from different disciplines, to build a wide and thick theoretic base for supporting the multi-discipline research. The multi-scale scratch analysis combines supporting bases coming from applied mathematics, geophysics, and information science respectively.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20154","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220449","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}
Fracture development and distribution in underground rocks have strong influence on rock properties, understanding the fracture system is critical to the oil and gas reservoir detection and production, groundwater resource, underground wastes storage, mining, seismology and CO2 capture and storage.Due to the complex fracture distribution and geometry in nature rocks, the lack of information about fracture parameters (fracture density, length and thickness) makes the nature rock cannot be used in laboratory experiments. Rock physics experiments require the controlled and known fracture parameters and orientation in rock samples, thus synthetic samples were used to represent fractured rocks in several previous studies. However, the fractures were represented by other week material, such as silica rubber imbedded in epoxy solid, to simulate the fractured rocks in previous studies. The materials used to construct the samples (Lucite, silica rubber, sand bonded by epoxy) were very different from nature rocks, the solid representing background matrix and the week material representing fractures have no porous and fracture space and saturated fluids. In this study, we use new construction method based on material science progress to build synthetic samples which have similar mineral component, porous structure, cementation as nature rocks. The synthetic rock containing controlled fracture geometry provides a different way to create fractured rocks to observe the seismic anisotropy influenced by fracture parameters and fluids. The synthetic rocks are tested under high pressure to observe the pressure sensitivity, and SEM is used to observe the porous structure and fractures distrubution. We build a set of synthetic rocks to observe the effect of fractures upon seismic wave velocity and anisotropy. The samples are measured with 0.5 MHz transducers. P and S wave velocity in different propagation directions of these four samples are measured when saturated by air and water.The experimental results can help in investigating the relationship between fracture density and P and S wave anisotropy in fractured reservoirs. The measurement results show that the P wave velocity and anisotropy is significantly influenced by saturating fluid. Shear wave velocity, shear wave splitting and shear wave anisotropy are less sensitive to saturating fluid but significantly affected by fracture density. P wave velocities in perpendicular direction show significant influences of fracture, the velocity decreases as the fracture density increases. Shear wave velocity in perpendicular direction decreases with the increasing fracture density, the difference between fast shear wave and slow shear wave velocity is smaller in this direction. However the slow shear wave velocity is more sensitive to fracture density than fast shear wave velocity in parallel direction, thus the difference of fast and slow shear wave velocity in parallel direction increases as the fracture density increa
{"title":"Experimental research on the effects of crack density based on synthetic sandstones contain controlled fractures","authors":"P. Ding, B. Di, Jianxin Wei, Xiang-Yang Li","doi":"10.6038/CJG20150425","DOIUrl":"https://doi.org/10.6038/CJG20150425","url":null,"abstract":"Fracture development and distribution in underground rocks have strong influence on rock properties, understanding the fracture system is critical to the oil and gas reservoir detection and production, groundwater resource, underground wastes storage, mining, seismology and CO2 capture and storage.Due to the complex fracture distribution and geometry in nature rocks, the lack of information about fracture parameters (fracture density, length and thickness) makes the nature rock cannot be used in laboratory experiments. Rock physics experiments require the controlled and known fracture parameters and orientation in rock samples, thus synthetic samples were used to represent fractured rocks in several previous studies. However, the fractures were represented by other week material, such as silica rubber imbedded in epoxy solid, to simulate the fractured rocks in previous studies. The materials used to construct the samples (Lucite, silica rubber, sand bonded by epoxy) were very different from nature rocks, the solid representing background matrix and the week material representing fractures have no porous and fracture space and saturated fluids. In this study, we use new construction method based on material science progress to build synthetic samples which have similar mineral component, porous structure, cementation as nature rocks. The synthetic rock containing controlled fracture geometry provides a different way to create fractured rocks to observe the seismic anisotropy influenced by fracture parameters and fluids. The synthetic rocks are tested under high pressure to observe the pressure sensitivity, and SEM is used to observe the porous structure and fractures distrubution. We build a set of synthetic rocks to observe the effect of fractures upon seismic wave velocity and anisotropy. The samples are measured with 0.5 MHz transducers. P and S wave velocity in different propagation directions of these four samples are measured when saturated by air and water.The experimental results can help in investigating the relationship between fracture density and P and S wave anisotropy in fractured reservoirs. The measurement results show that the P wave velocity and anisotropy is significantly influenced by saturating fluid. Shear wave velocity, shear wave splitting and shear wave anisotropy are less sensitive to saturating fluid but significantly affected by fracture density. P wave velocities in perpendicular direction show significant influences of fracture, the velocity decreases as the fracture density increases. Shear wave velocity in perpendicular direction decreases with the increasing fracture density, the difference between fast shear wave and slow shear wave velocity is smaller in this direction. However the slow shear wave velocity is more sensitive to fracture density than fast shear wave velocity in parallel direction, thus the difference of fast and slow shear wave velocity in parallel direction increases as the fracture density increa","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71078739","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}
Zhang Xun-hua, Wang Zhong-lei, Hou Fang-hui, Yang Jin-yu, Guo Xing-Wei
Terrain is the situation of the ground rising and falling, which is controlled by both the endogenetic and exogenic forces of the earth. The terrain reflects the internal structure, construction, and evolution of the curst. Free-air gravity anomalies are related to topography and geomorphology. It is considered that the curst that under mountains is thicker than that under plains by the equalization principle. There is a mirror image relationship between crust thickness and terrain relief. The map series of geology and geophysics of China seas and land include figures of tectonic framework and evolution of tectonic framework. The temporal evolution of the main blocks is studied in both of the maps, which elaborate the evolution of China's terrain as a “Seesaw”. This paper analyzes the geomorphological features by the free-air gravity anomaly map and Moho depth distribution map. In accordance with the principle of tectonic landform classification, the general characteristics of China seas and land is viewed as a whole which shows five terrain steps from west to east on the basis of three geomorphological ladders of Chinese land.
{"title":"Terrain Evolution of China Seas and Land Since the Indo‐China Movement and Characteristics of the Stepped Landform","authors":"Zhang Xun-hua, Wang Zhong-lei, Hou Fang-hui, Yang Jin-yu, Guo Xing-Wei","doi":"10.1002/CJG2.20155","DOIUrl":"https://doi.org/10.1002/CJG2.20155","url":null,"abstract":"Terrain is the situation of the ground rising and falling, which is controlled by both the endogenetic and exogenic forces of the earth. The terrain reflects the internal structure, construction, and evolution of the curst. Free-air gravity anomalies are related to topography and geomorphology. It is considered that the curst that under mountains is thicker than that under plains by the equalization principle. There is a mirror image relationship between crust thickness and terrain relief. The map series of geology and geophysics of China seas and land include figures of tectonic framework and evolution of tectonic framework. The temporal evolution of the main blocks is studied in both of the maps, which elaborate the evolution of China's terrain as a “Seesaw”. This paper analyzes the geomorphological features by the free-air gravity anomaly map and Moho depth distribution map. In accordance with the principle of tectonic landform classification, the general characteristics of China seas and land is viewed as a whole which shows five terrain steps from west to east on the basis of three geomorphological ladders of Chinese land.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20155","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220462","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}
Yang Shouguo, Xie Fu-li, Gong Dan, Zhang Cheng-guang, Zhang Bixing
As the improvement of global oil and gas exploration,the fractural reservoir becomes one of the most important objects.The fractures complicatedly influence the array waveforms of logging because of the diversity distribution of fracture zone,which causes the recognition and evaluation become one of the most difficult problems in acoustic logging.In this paper,we research the acoustic field of the borehole surrounded by aporous formation with tilt fractures by numerical simulation,and also investigate the characteristics of borehole fields in the formations with different fracture parameters.We numerically simulate the acoustic fields excited by a point source in the borehole surrounded by aporous formation with tilt fractures using the 3-D staggered grid stress-velocity finite difference method.We design a non-uniform grid finite difference method in order to satisfy the computation of thin fractures,the precision and speed of calculation are improved significantly.We process the fluid inside fractures through setting the parameters of constitutive functions as fluid limitation,which uniforms the difference equations on the fluid-porous media boundary and makes the computation more flexible.We investigate and compare many parameters influencing on the array waveforms,such as fracture width,fracture zone width,tilt angle and permeability.By the computations and analysis of borehole acoustic fields in different conditions,we can get conclusions as follows:1.The fractures barely influence body waves because the fracture width is much less than the acoustic wavelength,but the reflected shear wave and reflected Stoneley wave still could exist when Stoneley wave goes through the fracture.2.When the fractures are horizontal,only reflected Stoneley wave can be observed if the source is low frequency(2.5kHz),while the reflected shear wave and reflected Stoneley wave both exist if the source is high frequency(5kHz and above).The amplitude of reflected Stoneley wave decreases when the width of fracture reduces,though the amplitude of reflected shear wave is unchanged.The reflected shear wave still exists when the fracture width reduces to 20 m.3.The density and width of fracture zone significantly influence the amplitude of reflected waves.When the density is small,the reflected waves are weak due to the low density causes the small fractures′interaction;as the density increasing,the reflected waves get stronger.4.When the fracture cross the borehole and tilt,the reflected shear wave disappears,however the reflected Stoneley wave still exists,this is good for testing tilt fractures.5.The attenuation of Stoneley waves increases along with the permeability increases.This causes the amplitude of inflected Stoneley waves on the fracture boundary decreases,so the reflected Stoneley wave could not be observed when the fractures are long away from source.In this paper,3-D non-uniform grid finite difference method is used to numerically simulate the acoustic field
{"title":"Borehole acoustic fields in porous formation with tilted thin fracture","authors":"Yang Shouguo, Xie Fu-li, Gong Dan, Zhang Cheng-guang, Zhang Bixing","doi":"10.6038/CJG20150128","DOIUrl":"https://doi.org/10.6038/CJG20150128","url":null,"abstract":"As the improvement of global oil and gas exploration,the fractural reservoir becomes one of the most important objects.The fractures complicatedly influence the array waveforms of logging because of the diversity distribution of fracture zone,which causes the recognition and evaluation become one of the most difficult problems in acoustic logging.In this paper,we research the acoustic field of the borehole surrounded by aporous formation with tilt fractures by numerical simulation,and also investigate the characteristics of borehole fields in the formations with different fracture parameters.We numerically simulate the acoustic fields excited by a point source in the borehole surrounded by aporous formation with tilt fractures using the 3-D staggered grid stress-velocity finite difference method.We design a non-uniform grid finite difference method in order to satisfy the computation of thin fractures,the precision and speed of calculation are improved significantly.We process the fluid inside fractures through setting the parameters of constitutive functions as fluid limitation,which uniforms the difference equations on the fluid-porous media boundary and makes the computation more flexible.We investigate and compare many parameters influencing on the array waveforms,such as fracture width,fracture zone width,tilt angle and permeability.By the computations and analysis of borehole acoustic fields in different conditions,we can get conclusions as follows:1.The fractures barely influence body waves because the fracture width is much less than the acoustic wavelength,but the reflected shear wave and reflected Stoneley wave still could exist when Stoneley wave goes through the fracture.2.When the fractures are horizontal,only reflected Stoneley wave can be observed if the source is low frequency(2.5kHz),while the reflected shear wave and reflected Stoneley wave both exist if the source is high frequency(5kHz and above).The amplitude of reflected Stoneley wave decreases when the width of fracture reduces,though the amplitude of reflected shear wave is unchanged.The reflected shear wave still exists when the fracture width reduces to 20 m.3.The density and width of fracture zone significantly influence the amplitude of reflected waves.When the density is small,the reflected waves are weak due to the low density causes the small fractures′interaction;as the density increasing,the reflected waves get stronger.4.When the fracture cross the borehole and tilt,the reflected shear wave disappears,however the reflected Stoneley wave still exists,this is good for testing tilt fractures.5.The attenuation of Stoneley waves increases along with the permeability increases.This causes the amplitude of inflected Stoneley waves on the fracture boundary decreases,so the reflected Stoneley wave could not be observed when the fractures are long away from source.In this paper,3-D non-uniform grid finite difference method is used to numerically simulate the acoustic field","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71078963","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}
The relief of the metamorphosed basement of the Precambrian and the thickness variation of the overlying sedimentary cover are very important for geology and exploration of energy and resources. The magnetic difference between these two layers permits geophysicists to estimate the magnetic basement depth using aeromagnetic data. The work is based on such data acquired by AGRS's aero geophysical surveys for more than 30 years over China mainland, covering more than 30 basins and areas. Our purpose is to compile the magnetic basement depth map for China mainland on a scale 1:1000000 with the data converted into the same coordinate system and scale. The resultant map shows that using E105° line as a boundary, the covers are thick in sedimentary depression areas of western China, mainly distributed in the Tarim basin, Junggar basin, Qaidam basin and Tibet area. While, in east China, mainly distributed in the Songliao basin, Erlian basin, Ordos, southern North China, Sichuan basin, and South Yellow Sea-Subei basin, such covers are relatively thin in sedimentary depression areas, of which the largest thickness is located in the southwest of the Sichuan basin and the western edge of the Ordos basin. These characteristics are associated with the metamorphosed basement of Precambrian and depth changes of irruptive rocks body with certain scales, and reflect sedimentary covers' thickness and status. They allow us to intuitively observe depths and sizes of various types of sedimentary basins and sedimentary depression areas, and provide direct evidence for exploration of oil and gas reservoirs on the basements.
{"title":"Characteristics of Magnetic Basement Depth Beneath China Mainland","authors":"Xiong Sheng-qing, Ding Yan‐Yun, Li Zhan-kui","doi":"10.1002/CJG2.20156","DOIUrl":"https://doi.org/10.1002/CJG2.20156","url":null,"abstract":"The relief of the metamorphosed basement of the Precambrian and the thickness variation of the overlying sedimentary cover are very important for geology and exploration of energy and resources. The magnetic difference between these two layers permits geophysicists to estimate the magnetic basement depth using aeromagnetic data. The work is based on such data acquired by AGRS's aero geophysical surveys for more than 30 years over China mainland, covering more than 30 basins and areas. Our purpose is to compile the magnetic basement depth map for China mainland on a scale 1:1000000 with the data converted into the same coordinate system and scale. The resultant map shows that using E105° line as a boundary, the covers are thick in sedimentary depression areas of western China, mainly distributed in the Tarim basin, Junggar basin, Qaidam basin and Tibet area. While, in east China, mainly distributed in the Songliao basin, Erlian basin, Ordos, southern North China, Sichuan basin, and South Yellow Sea-Subei basin, such covers are relatively thin in sedimentary depression areas, of which the largest thickness is located in the southwest of the Sichuan basin and the western edge of the Ordos basin. These characteristics are associated with the metamorphosed basement of Precambrian and depth changes of irruptive rocks body with certain scales, and reflect sedimentary covers' thickness and status. They allow us to intuitively observe depths and sizes of various types of sedimentary basins and sedimentary depression areas, and provide direct evidence for exploration of oil and gas reservoirs on the basements.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/CJG2.20156","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51220511","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}
On February 12 2014,an Ms7.3earthquake hit Yutian,Xinjiang,the epicenter is at the intersection of Karakax fault and Gonggacuo fault.Earthquake triggering theory indicates that Coulomb stress on nearby faults will change because of crustal coseismic slip after earthquake,and it will affect earthquake potential risk.In this paper,we estimate focal mechanism and rupture process with far field seismic wave data,and calculate coseismic stress change on nearby faults around epicenter.The purpose is to discuss Coulomb stress change and seismic potential hazard on these faults caused by Yutian earthquake.After the earthquake,we download seismic far field wave data of which epicenter is between 30°to 90°from IRIS.We select27 high SNR(signal to noise ratio)seismic record to make theoretical seismogram.We use generalized ray theory to get synthetic seismic wave map,and sub fault parameter inverse process is based on simulated annealing algorithms.In the way of changing fault parameter to fit actual and synthetic wave form,optimum solution of every sub fault is found.Based on fault rupture inversion model and infinite elastic half space theory,we calculate Coulomb stress change on nearby faults caused by the earthquake.The inversion results show that source depth of earthquake is 10 km,dip angle is 71.9°,largest coseismic displacement is 210 cm.Seismic moment is 2.91×1019 N·m,the main seismic energy is released in former 10 second.Aftershocks are mainly distributed in three regions:north Pulu fault,east Karakax fault and centre Gonggacuo fault.Stress increased significantly on western segment of Altyn fault,central part of Pulu fault,eastern segment of Karakax fault and central segment of Gonggacuo fault.Among them the largest stress change is 0.05 MPa on Karakax fault and 0.04 MPa on Gonggacuo fault.Former research shows that,Coulomb stress change caused by earthquake larger than 0.01 MPa will dramatically increase seismic risk on faults.In our research,stress change on Pulu fault,Gonggacuo fault and Karakax fault exceed triggering threshold,so all these three faults have seismic risk.In the near future seismic potential hazard on these faults should be closely monitored.In the past 6years,3 moderately strong earthquakes happen in the study area,epicenters migrate from Gonggacuo fault to Altyn fault,from southwest to northeast.Though stress change on Altyn fault is much lower,in consideration of 9mm·a-1 slip rate,seismic risk on Altyn fault should cause enough attention.
{"title":"Rupture process of 12 February 2014, Yutian M(w)6. 9 earthquake and stress change on nearby faults","authors":"Y. Zhou, Wm Wang, L. Xiong, Jk He","doi":"10.6038/CJG20150116","DOIUrl":"https://doi.org/10.6038/CJG20150116","url":null,"abstract":"On February 12 2014,an Ms7.3earthquake hit Yutian,Xinjiang,the epicenter is at the intersection of Karakax fault and Gonggacuo fault.Earthquake triggering theory indicates that Coulomb stress on nearby faults will change because of crustal coseismic slip after earthquake,and it will affect earthquake potential risk.In this paper,we estimate focal mechanism and rupture process with far field seismic wave data,and calculate coseismic stress change on nearby faults around epicenter.The purpose is to discuss Coulomb stress change and seismic potential hazard on these faults caused by Yutian earthquake.After the earthquake,we download seismic far field wave data of which epicenter is between 30°to 90°from IRIS.We select27 high SNR(signal to noise ratio)seismic record to make theoretical seismogram.We use generalized ray theory to get synthetic seismic wave map,and sub fault parameter inverse process is based on simulated annealing algorithms.In the way of changing fault parameter to fit actual and synthetic wave form,optimum solution of every sub fault is found.Based on fault rupture inversion model and infinite elastic half space theory,we calculate Coulomb stress change on nearby faults caused by the earthquake.The inversion results show that source depth of earthquake is 10 km,dip angle is 71.9°,largest coseismic displacement is 210 cm.Seismic moment is 2.91×1019 N·m,the main seismic energy is released in former 10 second.Aftershocks are mainly distributed in three regions:north Pulu fault,east Karakax fault and centre Gonggacuo fault.Stress increased significantly on western segment of Altyn fault,central part of Pulu fault,eastern segment of Karakax fault and central segment of Gonggacuo fault.Among them the largest stress change is 0.05 MPa on Karakax fault and 0.04 MPa on Gonggacuo fault.Former research shows that,Coulomb stress change caused by earthquake larger than 0.01 MPa will dramatically increase seismic risk on faults.In our research,stress change on Pulu fault,Gonggacuo fault and Karakax fault exceed triggering threshold,so all these three faults have seismic risk.In the near future seismic potential hazard on these faults should be closely monitored.In the past 6years,3 moderately strong earthquakes happen in the study area,epicenters migrate from Gonggacuo fault to Altyn fault,from southwest to northeast.Though stress change on Altyn fault is much lower,in consideration of 9mm·a-1 slip rate,seismic risk on Altyn fault should cause enough attention.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71078586","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}
A strong earthquake(Mw6.9)occurred in the Gorda plate off the northwestern coast of California in March 10,2014(Beijing Time).The rupture process of the earthquake is determined by the waveform inversion method using far-field body waveform records provided by IRIS.Afterthat,we analyze the reason why the earthquake did not cause serious hazards and trigger tsunami,and provide new evidence to the research of dynamics study in the area.The focal mechanism of the earthquake is obtained by dislocation source model utilizing 19far-field P vertical waveform records with uniform azimuth coverage and 13near-field P-wave initial motions.Based on the obtained focal mechanism,we get the strike angle of fault rupture surface combined with the geological structure background.In the following finite fault inversion,the fault surface is divided into 17×9subfaults to simulate the temporal and spatial distribution of the slips,along with the use of 18far-field P vertical waveform records and 21 farfield SH tangent waveform records,then we can retrieve the rupture process of the earthquake using waveform inversion method with the multi-reflection effect under consideration.Based on the seawater-layered model,the focal mechanism solution based on the shear dislocation source model indicates that this event occurred on the rupture plane(strike angle 323°,dip angle 86.1°,rake angle-180°,focal depth 10.6km)is a high-angle strike-slip faulting.The rupture process is rather simple,the distribution of major slips is concentered in the region of35km×9km above the source,the rupture lasts about 19 seconds,the average rupture velocity is about 2.7km·s-1,the larger slips distribute along the strike direction,and the maximum slip is 249 cm.The earthquake is an Mw6.9strike-slip event with steep dip angle that occurs in the Gorda plate.The earthquake is a pure strike-slip faulting event occurring beneath the seabed,the fault surface is nearly vertical,so it did not cause great damage to the cities off the coast.Since the earthquake does not change the topography of the seafloor in the rupture process,so there is no big displacement of seawater,thus,it won′t trigger a large-scale tsunami.
{"title":"Rupture process of March 10, 2014, M(w)6. 9 Earthquake in the northwestern coast of California","authors":"L. Cao, J. Hao, Weimin Wang, Z. Yao","doi":"10.6038/CJG20150117","DOIUrl":"https://doi.org/10.6038/CJG20150117","url":null,"abstract":"A strong earthquake(Mw6.9)occurred in the Gorda plate off the northwestern coast of California in March 10,2014(Beijing Time).The rupture process of the earthquake is determined by the waveform inversion method using far-field body waveform records provided by IRIS.Afterthat,we analyze the reason why the earthquake did not cause serious hazards and trigger tsunami,and provide new evidence to the research of dynamics study in the area.The focal mechanism of the earthquake is obtained by dislocation source model utilizing 19far-field P vertical waveform records with uniform azimuth coverage and 13near-field P-wave initial motions.Based on the obtained focal mechanism,we get the strike angle of fault rupture surface combined with the geological structure background.In the following finite fault inversion,the fault surface is divided into 17×9subfaults to simulate the temporal and spatial distribution of the slips,along with the use of 18far-field P vertical waveform records and 21 farfield SH tangent waveform records,then we can retrieve the rupture process of the earthquake using waveform inversion method with the multi-reflection effect under consideration.Based on the seawater-layered model,the focal mechanism solution based on the shear dislocation source model indicates that this event occurred on the rupture plane(strike angle 323°,dip angle 86.1°,rake angle-180°,focal depth 10.6km)is a high-angle strike-slip faulting.The rupture process is rather simple,the distribution of major slips is concentered in the region of35km×9km above the source,the rupture lasts about 19 seconds,the average rupture velocity is about 2.7km·s-1,the larger slips distribute along the strike direction,and the maximum slip is 249 cm.The earthquake is an Mw6.9strike-slip event with steep dip angle that occurs in the Gorda plate.The earthquake is a pure strike-slip faulting event occurring beneath the seabed,the fault surface is nearly vertical,so it did not cause great damage to the cities off the coast.Since the earthquake does not change the topography of the seafloor in the rupture process,so there is no big displacement of seawater,thus,it won′t trigger a large-scale tsunami.","PeriodicalId":55257,"journal":{"name":"地球物理学报","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71078702","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}
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