Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at th...Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at the north of the Cangxian uplift in the North China Basin,the concentrated geothermal resource development zone in North China.This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years,on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed.The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area.As a result,the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault.The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average,the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend.However,the water quality has been stable for many years without any apparent changes.This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.展开更多
Characterizing the subsurface structure is an important parameter for the improvement of seismic hazard assessment.Due to the tectonic complexity of the earth,some deep fractures do not reach the earth's surface a...Characterizing the subsurface structure is an important parameter for the improvement of seismic hazard assessment.Due to the tectonic complexity of the earth,some deep fractures do not reach the earth's surface and are not detectable with visual analysis.Therefore,the lack of knowledge of faults and fractures can result in disasters,especially in urban planning.Many geophysical methods can be used to estimate subsurface structure characterization.However,a more reliable method is required to assess seismic hazards and reduce potential damage in metropolitan areas without destroying buildings and structures.This paper aims to identify hidden faults and structures using shear wave velocity sections.To do this,surface wave dispersion curve was extracted from the vertical component of microtremor array recording using the spatial autocorrelation(SPAC)method in two profiles and 13 array stations(perpendicular to the altitudes)to obtain shear wave velocity structure(Vs)in the west of Mashhad,northeast of Iran.The results of shear wave velocity profiles(Vs)indicate sudden changes in the thickness of sediments.This can be related to the displacement of a normal fault in this area causing the bottom rock to fall and an increase in the alluvial thickness in the central part of the plain.The velocity in the floor rock is 2000 meters per second in this area.According to the surface outcrops and water wells data,its material is slate and Phyllite metamorphic rocks that are exposed in the adjacent heights.Besides,the seismic profile results were well consistent with electrical resistance data and well logs indicating that the tool array method is flexible,non-invasive,relatively fast,and effective for urban areas with satisfactory accuracy.展开更多
The Tanlu Fault Zone(TLFZ),recognized as the largest active strike-slip fault system in eastern China,exhibits distinct structural features and seismic activities across its various segments.To elucidate the structura...The Tanlu Fault Zone(TLFZ),recognized as the largest active strike-slip fault system in eastern China,exhibits distinct structural features and seismic activities across its various segments.To elucidate the structural characteristics of the upper and middle crust in the Zhangbaling Uplift(ZBU)segment of the TLFZ,we employed ambient noise data collected from a dense seismic array comprising 192 nodes,deployed in 2020.Utilizing ambient noise tomography,we derived a three-dimensional S-wave velocity(Vs)structure of the region,extending to a depth of 10 km.The tomographic results reveal a prominent low-velocity anomaly at depths of 0–2 km along the fault zone,which correlates with the fault graben structure.According to the Vscharacteristics,the Mingguang Graben in the northern part of Zhangbaling extends to a depth of 3 km,whereas on the eastern flank of the Hefei Basin in the south,it reaches 1.5 km.Additionally,several NW-trending low-velocity stripes are identified at depths of 3–5 km on the eastern side of the Bengbu Uplift and the Hefei Basin,likely corresponding to NW-trending left-lateral hidden faults.By integrating the regional velocity structure,surface GPS directions,and earthquake focal mechanisms,we proposed a tectonic model for the Zhangbaling segment of the TLFZ.This model suggests that the NWtrending hidden faults may play a crucial role in modulating the near east-west stress loading on the TLFZ.展开更多
Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters.In process of data processing,we obtained a high-qualitative shallow seismic reflection sounding profil...Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters.In process of data processing,we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such as filtering,edition surgical blanking,prediction deconvolution,fitting static correlation of first arrival time,and velocity analysis.Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75~80 m,in the Middle Pleistocene deposits dated to be about 220 ka BP.The continuity,discontinuity,increasing and decreasing amount of reflection wave groups and change of their configurations,in combination with geological columns of drills,permitted us to know that the width of upper termination of the fault zone is 100 m.It can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is 200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene.No tectonic movement,which offset the covering deposits,had occurred since the late stage of Middle Pleistocene.展开更多
Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurr...Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurred along the middle segment of Longmenshan fault zone on November 30, 1999, the distribution of focal depth section, the stress release and seismicity features are given to reveal the earthquake-generating structure of the earthquake sequence. The obtained results show the activity features for this sequence as follows: ① There is no obvious foreshock, the accumulated strain energy releases in nearly pulse way, fluctuation of the seismic activity level is not quite evident during the duration of the sequence, and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation; ② The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground, but near the hidden Longmenshan piedmont faults. The direction of epicenter distribution is not very coincident with the fault strikes. The microscopic epicenters are relatively far from the macroscopic epicenters. The focal depths range from 5km to 16km; ③ The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction. From these, we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.展开更多
Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum...Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum organizations in Sichuan and of the results of seismic prospecting and detailed exploration in Chengdu depression during the last 20 years permitted us to study the types and distribution of hidden structures in Chengdu depression and its adjacent areas, in particular, to identify in detail the “hidden faults" in the Chenngdu-Deyang area on the one hand; The obtained data indicate that the NE-trending Xinjin fault runs northward and dies out in the south of Penzhen town of Shuangliu County. Meanwhile, we studied genetic relations of seismic activity to active faults and their corresponding movement characteristics on the other hand. Moreover, the surface faults and deep-seated faults are clearly defined and outlined, and 5 types of seismogenic faults suggested. The knowledge thus obtained enables us to delimit the focal zones for potential strong earthquakes in Chengdu depression. The study suggests that a zone of 40 km wide and more than 100 km long on sides along the Chengdu-Deyang line has a stable seismogeological background and good engineering-seismological conditions.展开更多
Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows h...Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows have been drilled and completed successively in the Middle Permian Qixia Fm and Middle Devonian Guanwushan Fm,etc.Along with the steady progress of exploration there,to make a further in-depth study on the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures will be of great significance to both a better understanding of Upper Paleozoic gas reservoirs in this study area and the expansion of oil and gas exploration field.In view of this,based on the newly deployed 3D seismic surveys,gravity–magnetic–electronic data,and practical drilling information from exploration wells like Well ST 9,the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures are analyzed as well as the features of the buried structures,gas reservoir forming conditions and exploration prospect there.The following findings were obtained:(1)A huge buried structure belt is developed underlying the Longmenshan front fault belt No.1(LSFFB 1)and marine strata are thus formed below the Lower Triassic Jialingjiang Fm due to the roles of compressive folding,extrusion and deformation;(2)The detachment horizons from LSFFB 1 go from shallower in the south to deeper in the north,turning from Cambrian slipping in the south to basement-involved in the north.The Paleozoic and its overlying strata were overall uplifted with a higher degree northward and so did the strata between the up-thrown and down-thrown sides of the faults with a greater displacement distance and higher folding degree,resulting in that the Paleozoic strata in the north are 1500 higher uplifted than those in the south;(3)In the western Jiange and Guangyuan areas,the eastern LSFFB 1 presents a tectonic pattern of“three steps”as a whole.In conclusion,there are good gas reservoir forming conditions in LSFFB 1,the down-thrown sides of which cover an area of 1800 km2,where the Guanwushan Fm and Qixia Fm provide good accumulation and preservation conditions for gas reservoirs,which will become favorable gas exploration targets in the deep marine strata in NW Sichuan Basin.展开更多
洛杉矶是美国西海岸的一座大城市,处在一个地震多发地带。科学家们发现了洛杉矶地下的一个隐蔽的断层,并确认该断层是过去该市遭受地震灾害的元凶,还预言今后此断层将会造成更强烈的地震。这则消息无疑会在洛杉矶市民心头蒙上一层阴影,...洛杉矶是美国西海岸的一座大城市,处在一个地震多发地带。科学家们发现了洛杉矶地下的一个隐蔽的断层,并确认该断层是过去该市遭受地震灾害的元凶,还预言今后此断层将会造成更强烈的地震。这则消息无疑会在洛杉矶市民心头蒙上一层阴影,当然,对洛杉矶的房地产商人来说也许打击更大。本文涉及了不少地理知识,其中最有用的也许是:The amount of damage that a quake can do depends not only on its magnitude(量级),but its depth and the type of structures on the surface.】展开更多
基金funded by Public Interest Monitoring Project(No.XCSD-2024-317)of the Tianjin Municipal Bureau of Planning and Natural Resources。
文摘Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at the north of the Cangxian uplift in the North China Basin,the concentrated geothermal resource development zone in North China.This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years,on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed.The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area.As a result,the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault.The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average,the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend.However,the water quality has been stable for many years without any apparent changes.This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.
文摘Characterizing the subsurface structure is an important parameter for the improvement of seismic hazard assessment.Due to the tectonic complexity of the earth,some deep fractures do not reach the earth's surface and are not detectable with visual analysis.Therefore,the lack of knowledge of faults and fractures can result in disasters,especially in urban planning.Many geophysical methods can be used to estimate subsurface structure characterization.However,a more reliable method is required to assess seismic hazards and reduce potential damage in metropolitan areas without destroying buildings and structures.This paper aims to identify hidden faults and structures using shear wave velocity sections.To do this,surface wave dispersion curve was extracted from the vertical component of microtremor array recording using the spatial autocorrelation(SPAC)method in two profiles and 13 array stations(perpendicular to the altitudes)to obtain shear wave velocity structure(Vs)in the west of Mashhad,northeast of Iran.The results of shear wave velocity profiles(Vs)indicate sudden changes in the thickness of sediments.This can be related to the displacement of a normal fault in this area causing the bottom rock to fall and an increase in the alluvial thickness in the central part of the plain.The velocity in the floor rock is 2000 meters per second in this area.According to the surface outcrops and water wells data,its material is slate and Phyllite metamorphic rocks that are exposed in the adjacent heights.Besides,the seismic profile results were well consistent with electrical resistance data and well logs indicating that the tool array method is flexible,non-invasive,relatively fast,and effective for urban areas with satisfactory accuracy.
基金supported by the National Key R&D Program of China(Grant No.2022YFF0800701)the Joint Open Fund of Mengcheng National Geophysical Observatory(Grant No.MENGO-202002)+1 种基金the National Natural Science Foundation of China(Grant No.42104063)the Earthquake Spark Program Project of China Earthquake Administration(Grant No.XH24020B)。
文摘The Tanlu Fault Zone(TLFZ),recognized as the largest active strike-slip fault system in eastern China,exhibits distinct structural features and seismic activities across its various segments.To elucidate the structural characteristics of the upper and middle crust in the Zhangbaling Uplift(ZBU)segment of the TLFZ,we employed ambient noise data collected from a dense seismic array comprising 192 nodes,deployed in 2020.Utilizing ambient noise tomography,we derived a three-dimensional S-wave velocity(Vs)structure of the region,extending to a depth of 10 km.The tomographic results reveal a prominent low-velocity anomaly at depths of 0–2 km along the fault zone,which correlates with the fault graben structure.According to the Vscharacteristics,the Mingguang Graben in the northern part of Zhangbaling extends to a depth of 3 km,whereas on the eastern flank of the Hefei Basin in the south,it reaches 1.5 km.Additionally,several NW-trending low-velocity stripes are identified at depths of 3–5 km on the eastern side of the Bengbu Uplift and the Hefei Basin,likely corresponding to NW-trending left-lateral hidden faults.By integrating the regional velocity structure,surface GPS directions,and earthquake focal mechanisms,we proposed a tectonic model for the Zhangbaling segment of the TLFZ.This model suggests that the NWtrending hidden faults may play a crucial role in modulating the near east-west stress loading on the TLFZ.
基金A High-new Technique Project by State Development and Planning Commission of China (2001977).
文摘Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters.In process of data processing,we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such as filtering,edition surgical blanking,prediction deconvolution,fitting static correlation of first arrival time,and velocity analysis.Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75~80 m,in the Middle Pleistocene deposits dated to be about 220 ka BP.The continuity,discontinuity,increasing and decreasing amount of reflection wave groups and change of their configurations,in combination with geological columns of drills,permitted us to know that the width of upper termination of the fault zone is 100 m.It can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is 200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene.No tectonic movement,which offset the covering deposits,had occurred since the late stage of Middle Pleistocene.
文摘Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurred along the middle segment of Longmenshan fault zone on November 30, 1999, the distribution of focal depth section, the stress release and seismicity features are given to reveal the earthquake-generating structure of the earthquake sequence. The obtained results show the activity features for this sequence as follows: ① There is no obvious foreshock, the accumulated strain energy releases in nearly pulse way, fluctuation of the seismic activity level is not quite evident during the duration of the sequence, and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation; ② The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground, but near the hidden Longmenshan piedmont faults. The direction of epicenter distribution is not very coincident with the fault strikes. The microscopic epicenters are relatively far from the macroscopic epicenters. The focal depths range from 5km to 16km; ③ The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction. From these, we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.
文摘Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum organizations in Sichuan and of the results of seismic prospecting and detailed exploration in Chengdu depression during the last 20 years permitted us to study the types and distribution of hidden structures in Chengdu depression and its adjacent areas, in particular, to identify in detail the “hidden faults" in the Chenngdu-Deyang area on the one hand; The obtained data indicate that the NE-trending Xinjin fault runs northward and dies out in the south of Penzhen town of Shuangliu County. Meanwhile, we studied genetic relations of seismic activity to active faults and their corresponding movement characteristics on the other hand. Moreover, the surface faults and deep-seated faults are clearly defined and outlined, and 5 types of seismogenic faults suggested. The knowledge thus obtained enables us to delimit the focal zones for potential strong earthquakes in Chengdu depression. The study suggests that a zone of 40 km wide and more than 100 km long on sides along the Chengdu-Deyang line has a stable seismogeological background and good engineering-seismological conditions.
基金supported by the National Major Science and Technology Project“Enrichment law and target evaluation of large gas fields in Permian-Middle Triassic in Sichuan Basin”(No.:2016ZX05007004)the CNPC Major Science and Technology Project“Study and application of key techniques for 30 billion m^(3)gas production in PetroChina Southwest Oil&Gas Field Company”(No.:2016E-06).
文摘Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows have been drilled and completed successively in the Middle Permian Qixia Fm and Middle Devonian Guanwushan Fm,etc.Along with the steady progress of exploration there,to make a further in-depth study on the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures will be of great significance to both a better understanding of Upper Paleozoic gas reservoirs in this study area and the expansion of oil and gas exploration field.In view of this,based on the newly deployed 3D seismic surveys,gravity–magnetic–electronic data,and practical drilling information from exploration wells like Well ST 9,the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures are analyzed as well as the features of the buried structures,gas reservoir forming conditions and exploration prospect there.The following findings were obtained:(1)A huge buried structure belt is developed underlying the Longmenshan front fault belt No.1(LSFFB 1)and marine strata are thus formed below the Lower Triassic Jialingjiang Fm due to the roles of compressive folding,extrusion and deformation;(2)The detachment horizons from LSFFB 1 go from shallower in the south to deeper in the north,turning from Cambrian slipping in the south to basement-involved in the north.The Paleozoic and its overlying strata were overall uplifted with a higher degree northward and so did the strata between the up-thrown and down-thrown sides of the faults with a greater displacement distance and higher folding degree,resulting in that the Paleozoic strata in the north are 1500 higher uplifted than those in the south;(3)In the western Jiange and Guangyuan areas,the eastern LSFFB 1 presents a tectonic pattern of“three steps”as a whole.In conclusion,there are good gas reservoir forming conditions in LSFFB 1,the down-thrown sides of which cover an area of 1800 km2,where the Guanwushan Fm and Qixia Fm provide good accumulation and preservation conditions for gas reservoirs,which will become favorable gas exploration targets in the deep marine strata in NW Sichuan Basin.
文摘洛杉矶是美国西海岸的一座大城市,处在一个地震多发地带。科学家们发现了洛杉矶地下的一个隐蔽的断层,并确认该断层是过去该市遭受地震灾害的元凶,还预言今后此断层将会造成更强烈的地震。这则消息无疑会在洛杉矶市民心头蒙上一层阴影,当然,对洛杉矶的房地产商人来说也许打击更大。本文涉及了不少地理知识,其中最有用的也许是:The amount of damage that a quake can do depends not only on its magnitude(量级),but its depth and the type of structures on the surface.】
