As an important indicator parameter of fluid identification,fluid factor has always been a concern for scholars.However,when predicting Russell fluid factor or effective pore-fluid bulk modulus,it is necessary to intr...As an important indicator parameter of fluid identification,fluid factor has always been a concern for scholars.However,when predicting Russell fluid factor or effective pore-fluid bulk modulus,it is necessary to introduce a new rock skeleton parameter which is the dry-rock VP/VS ratio squared(DVRS).In the process of fluid factor calculation or inversion,the existing methods take this parameter as a static constant,which has been estimated in advance,and then apply it to the fluid factor calculation and inversion.The fluid identification analysis based on a portion of the Marmousi 2 model and numerical forward modeling test show that,taking the DVRS as a static constant will limit the identification ability of fluid factor and reduce the inversion accuracy.To solve the above problems,we proposed a new method to regard the DVRS as a dynamic variable varying with depth and lithology for the first time,then apply it to fluid factor calculation and inversion.Firstly,the exact Zoeppritz equations are rewritten into a new form containing the fluid factor and DVRS of upper and lower layers.Next,the new equations are applied to the four parameters simultaneous inversion based on the generalized nonlinear inversion(GNI)method.The testing results on a portion of the Marmousi 2 model and field data show that dynamic DVRS can significantly improve the fluid factor identification ability,effectively suppress illusion.Both synthetic and filed data tests also demonstrate that the GNI method based on Bayesian deterministic inversion(BDI)theory can successfully solve the above four parameter simultaneous inversion problem,and taking the dynamic DVRS as a target inversion parameter can effectively improve the inversion accuracy of fluid factor.All these results completely verified the feasibility and effectiveness of the proposed method.展开更多
The Hi-CLIMB seismic array is located in the central-western Tibetan Plateau.The H-κ-c method(Li JT et al.,2019)was applied to receiver function data on the HiCLIMB,which corrects the back-azimuthal variations in the...The Hi-CLIMB seismic array is located in the central-western Tibetan Plateau.The H-κ-c method(Li JT et al.,2019)was applied to receiver function data on the HiCLIMB,which corrects the back-azimuthal variations in the arrival times of Ps and crustal multiples caused by crustal anisotropy and dipping interfaces before performing H-κstacking.Compared to the traditional H-κmethod,the H-κstacking results after harmonic corrections showed considerable improvements,including greatly reduced errors,significantly less scattered H(crustal thickness)andκ(crustal v_(P)/v_(S)ratio)values,and clearer patterns of H andκin different Tibetan blocks.This demonstrates that the H-κ-c method works well even for regions with complex crustal structures,such as the Tibetan Plateau,when there are helpful references from nearby stations or other constraints.The variation in crustal thickness agrees with previous studies but tends to be relatively shallower beneath most of the plateau.Two regions with particularly high crustal v_(P)/v_(S)were observed,namely,one in the northern Himalaya block and beneath the YarlungZangbo suture,and the other in the Qiangtang block.Their correlation with mid-crust low S velocities from previous studies suggests the possible presence of fluid or partial melt in the two regions,which may have implications for the crustal flow model.In contrast,the Lhasa block had relatively lower crustal v_(P)/v_(S)and relatively higher crustal S velocity within the plateau,which is interpreted to be mechanically stronger than the Himalaya and Qiangtang blocks,and without mid-crust partial melt.展开更多
The North China Craton(NCC)is one of the oldest cratons on earth.Several important tectonic transformations of MesozoicCenozoic tectonic regime led to the destruction of the North China craton.The knowledge of crustal...The North China Craton(NCC)is one of the oldest cratons on earth.Several important tectonic transformations of MesozoicCenozoic tectonic regime led to the destruction of the North China craton.The knowledge of crustal structure can provide important constraints for the formation and evolution of cratons.New maps of sediment thickness,crustal thickness(H)and v_(P)/v_(S)(κ)in the central and western NCC were obtained using sequential H-κstacking.P-wave receiver functions are calculated using teleseismic waveform data recorded by 405 stations from Chin Array project.Benefiting from the densely distribution of temporary seismic stations,our results reveal details of the crustal structure in the study area.The thickness of sedimentary layer in North China ranges from 0–6.4 km,and the thickest sedimentary layer is in Ordos block and its surroundings(about 2.8–6 km);The thickness of sedimentary layer in the Mongolia fold belt and Yinshan orogenic belt is relatively thin(less than 1 km).The crustal thickness of the study area varies between 27–48 km,of which the crust of the North China Plain is about 30–33 km,the central NCC is about 33–40 km,and the Ordos block is 40–48 km thick.The average v_(P)/v_(S)ratios in the study area is mostly between 1.66 and 1.90,and that in the Yanshan-Taihang mountain fold belt is between 1.70 and 1.85,and that in the Ordos block is between 1.65 and 1.90,with an average value of 1.77,indicating the absence of a thick basaltic lower crust.The obvious negative correlation between crustal thickness and average v_(P)/v_(S)ratio within Ordos and Central Asia orogenic belt may be related to magmatic underplating during the crustal formation.There is no significant correlation between the crustal thickness and the v_(P)/v_(S)ratio in the Lüliang-Taihang mountain fold belt,which may be related to the multiple geological processes such as underplating and crustal extension and thinning in this area.The lack of correlation between crust thickness and topography in the central orogenic belt and the North China Basin indicates the topography of these areas are controlled not only by crustal isostatic adjustment but also by the lithospheric mantle processes.展开更多
Geothermal resources are a promising approach to clean renewable energy;90%of them are deep reservoirs of hot dry rock that require hydraulic fracturing to create a network of connections among wells to enable efficie...Geothermal resources are a promising approach to clean renewable energy;90%of them are deep reservoirs of hot dry rock that require hydraulic fracturing to create a network of connections among wells to enable efficient heat exchange,known as an Enhanced Geothermal System(EGS).The Pohang EGS project in south Korea led to a devasting Mw5.5 earthquake,triggered by the reservoir's EGS stimulation,the largest earthquake known to have been induced by EGS development.Detailed investigations have been conducted to understand the cause of the Pohang earthquake;the conclusion has been that overpressurized injected fluids migrated into an unknown fault triggering this large earthquake.Detailed velocity images for the source zone of the 2017 Pohang earthquake,which could be helpful for further understanding its inducing mechanism,are unavailable.However,we have assembled detailed aftershock data recorded by 41 local stations installed within about three months after the Mw5.5 Pohang earthquake,and have then applied the V_(p)/V_(s)model's consistency-constrained double-difference seismic tomography method to determine the high-resolution three-dimensional Vp(compressional wave velocity),Vs(shear wave velocity),and V_(p)/V_(s)models of the source region that we report here,as well as earthquake locations within the source region.The velocity images reveal that the deep source area of the 2017 Pohang earthquake is dominated by low Vp,high Vs,and low V_(p)/V_(s)anomalies,a pattern that can be caused by overpressurized vapors due to high temperatures at these depths.Based on aftershock locations and velocity features,our studies support the conclusion that the 2017Pohang earthquake was triggered by injected EGS fluids that migrated into a blind fault.展开更多
The Yangbi M_(S)6.4 earthquake occurred on May 21,2021 in western Yunnan,China,where moderate earthquakes strike frequently.It exhibited a typical“foreshock-mainshock-aftershock”sequence and did not occur on a pre-e...The Yangbi M_(S)6.4 earthquake occurred on May 21,2021 in western Yunnan,China,where moderate earthquakes strike frequently.It exhibited a typical“foreshock-mainshock-aftershock”sequence and did not occur on a pre-existing active fault.The seismogenic environment and mechanism of this earthquake have aroused considerable research attention.In this study,we obtain the three-dimensional v_(P),v_(S)and v_(P)/v_(S)images using the v_(P)/v_(S)consistency-constrained double-difference tomography method,which improves the accuracy of v_(P)/v_(S)models.We focus on characteristics of v_(P)/v_(S)images in areas with a lateral resolution of 0.1°,and reveal the seismogenic environment of the Yangbi M_(S)6.4 earthquake.The conclusions are as follows:(1)Low velocity and high-v_(P)/v_(S)anomalies are revealed at different depths around the northern segment of the Red River fault.v_(S)and v_(P)/v_(S)images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature.(2)The source region of the Yangbi M_(S)6.4 earthquake is located in a low-v_(P)/v_(S)zone implying high medium strength.High-v_(P)/v_(S)anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts,which are unfavorable for stress accumulation and triggering large earthquakes.Such conditions have also prevented the earthquake sequence from extending northwestward.(3)With the southeastward extrusion of materials from the Tibetan Plateau,fluid migration was blocked by the low-v_(P)/v_(S)body in the source region.The high-v_(P)/v_(S)anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer,and preparing the largest foreshock in the transition zone of high to low v_(P)/v_(S).Meanwhile,tectonic stress incessantly accumulated in the brittle upper crust,eventually led to the M_(S)6.4 earthquake occurrence.展开更多
The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as G...The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as GHF and ZDF,respectively).Although the extension of the ZDF to the northeast,which represents the amalgamation of the two sub-blocks has been confirmed,the development of the GHF to the southwest remains to be verified.To better constrain the detailed deep structure beneath the southwest Cathaysia,which hold great significance for revealing the evolution of the SCB,a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin(SSB).Combining with the regional 10 permanent stations(PA),we obtained two profiles with teleseismic P-wave receiver function stacking.The most obvious feature in our results is the ascending Moho towards the coastal area,which is consistent with the passive margin continental and extensional tectonic setting.The stacking profile from the dense nodal array(DNA)shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB.We deduce that this offset may be casued by the deep extension of the GHF,which represents the remnants of the amalgamation of the Cathaysia block.From the other evidences,we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface.The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB.The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF,which serves as a channel for upwelling hot materials.展开更多
基金the National Natural Science Foundation of China(41904116,41874156,42074167 and 42204135)the Natural Science Foundation of Hunan Province(2020JJ5168)the China Postdoctoral Science Foundation(2021M703629)for their funding of this research.
文摘As an important indicator parameter of fluid identification,fluid factor has always been a concern for scholars.However,when predicting Russell fluid factor or effective pore-fluid bulk modulus,it is necessary to introduce a new rock skeleton parameter which is the dry-rock VP/VS ratio squared(DVRS).In the process of fluid factor calculation or inversion,the existing methods take this parameter as a static constant,which has been estimated in advance,and then apply it to the fluid factor calculation and inversion.The fluid identification analysis based on a portion of the Marmousi 2 model and numerical forward modeling test show that,taking the DVRS as a static constant will limit the identification ability of fluid factor and reduce the inversion accuracy.To solve the above problems,we proposed a new method to regard the DVRS as a dynamic variable varying with depth and lithology for the first time,then apply it to fluid factor calculation and inversion.Firstly,the exact Zoeppritz equations are rewritten into a new form containing the fluid factor and DVRS of upper and lower layers.Next,the new equations are applied to the four parameters simultaneous inversion based on the generalized nonlinear inversion(GNI)method.The testing results on a portion of the Marmousi 2 model and field data show that dynamic DVRS can significantly improve the fluid factor identification ability,effectively suppress illusion.Both synthetic and filed data tests also demonstrate that the GNI method based on Bayesian deterministic inversion(BDI)theory can successfully solve the above four parameter simultaneous inversion problem,and taking the dynamic DVRS as a target inversion parameter can effectively improve the inversion accuracy of fluid factor.All these results completely verified the feasibility and effectiveness of the proposed method.
基金the National Natural Science Foundation of China(Nos.U1939204,and 41774056).
文摘The Hi-CLIMB seismic array is located in the central-western Tibetan Plateau.The H-κ-c method(Li JT et al.,2019)was applied to receiver function data on the HiCLIMB,which corrects the back-azimuthal variations in the arrival times of Ps and crustal multiples caused by crustal anisotropy and dipping interfaces before performing H-κstacking.Compared to the traditional H-κmethod,the H-κstacking results after harmonic corrections showed considerable improvements,including greatly reduced errors,significantly less scattered H(crustal thickness)andκ(crustal v_(P)/v_(S)ratio)values,and clearer patterns of H andκin different Tibetan blocks.This demonstrates that the H-κ-c method works well even for regions with complex crustal structures,such as the Tibetan Plateau,when there are helpful references from nearby stations or other constraints.The variation in crustal thickness agrees with previous studies but tends to be relatively shallower beneath most of the plateau.Two regions with particularly high crustal v_(P)/v_(S)were observed,namely,one in the northern Himalaya block and beneath the YarlungZangbo suture,and the other in the Qiangtang block.Their correlation with mid-crust low S velocities from previous studies suggests the possible presence of fluid or partial melt in the two regions,which may have implications for the crustal flow model.In contrast,the Lhasa block had relatively lower crustal v_(P)/v_(S)and relatively higher crustal S velocity within the plateau,which is interpreted to be mechanically stronger than the Himalaya and Qiangtang blocks,and without mid-crust partial melt.
基金supported by the National Science Foundation of China(No.U1839210)。
文摘The North China Craton(NCC)is one of the oldest cratons on earth.Several important tectonic transformations of MesozoicCenozoic tectonic regime led to the destruction of the North China craton.The knowledge of crustal structure can provide important constraints for the formation and evolution of cratons.New maps of sediment thickness,crustal thickness(H)and v_(P)/v_(S)(κ)in the central and western NCC were obtained using sequential H-κstacking.P-wave receiver functions are calculated using teleseismic waveform data recorded by 405 stations from Chin Array project.Benefiting from the densely distribution of temporary seismic stations,our results reveal details of the crustal structure in the study area.The thickness of sedimentary layer in North China ranges from 0–6.4 km,and the thickest sedimentary layer is in Ordos block and its surroundings(about 2.8–6 km);The thickness of sedimentary layer in the Mongolia fold belt and Yinshan orogenic belt is relatively thin(less than 1 km).The crustal thickness of the study area varies between 27–48 km,of which the crust of the North China Plain is about 30–33 km,the central NCC is about 33–40 km,and the Ordos block is 40–48 km thick.The average v_(P)/v_(S)ratios in the study area is mostly between 1.66 and 1.90,and that in the Yanshan-Taihang mountain fold belt is between 1.70 and 1.85,and that in the Ordos block is between 1.65 and 1.90,with an average value of 1.77,indicating the absence of a thick basaltic lower crust.The obvious negative correlation between crustal thickness and average v_(P)/v_(S)ratio within Ordos and Central Asia orogenic belt may be related to magmatic underplating during the crustal formation.There is no significant correlation between the crustal thickness and the v_(P)/v_(S)ratio in the Lüliang-Taihang mountain fold belt,which may be related to the multiple geological processes such as underplating and crustal extension and thinning in this area.The lack of correlation between crust thickness and topography in the central orogenic belt and the North China Basin indicates the topography of these areas are controlled not only by crustal isostatic adjustment but also by the lithospheric mantle processes.
基金supported by the National Natural Science Foundation of China(42304056)the Natural Science Foundation of Hebei Province(D2023305007)+1 种基金supported by the Basic Research Project(GP2020-017,GP2020027)of the Korea Institute of Geoscience and Mineral Resources(KIGAM)funded by the Ministry of Science and ICT of Korea。
文摘Geothermal resources are a promising approach to clean renewable energy;90%of them are deep reservoirs of hot dry rock that require hydraulic fracturing to create a network of connections among wells to enable efficient heat exchange,known as an Enhanced Geothermal System(EGS).The Pohang EGS project in south Korea led to a devasting Mw5.5 earthquake,triggered by the reservoir's EGS stimulation,the largest earthquake known to have been induced by EGS development.Detailed investigations have been conducted to understand the cause of the Pohang earthquake;the conclusion has been that overpressurized injected fluids migrated into an unknown fault triggering this large earthquake.Detailed velocity images for the source zone of the 2017 Pohang earthquake,which could be helpful for further understanding its inducing mechanism,are unavailable.However,we have assembled detailed aftershock data recorded by 41 local stations installed within about three months after the Mw5.5 Pohang earthquake,and have then applied the V_(p)/V_(s)model's consistency-constrained double-difference seismic tomography method to determine the high-resolution three-dimensional Vp(compressional wave velocity),Vs(shear wave velocity),and V_(p)/V_(s)models of the source region that we report here,as well as earthquake locations within the source region.The velocity images reveal that the deep source area of the 2017 Pohang earthquake is dominated by low Vp,high Vs,and low V_(p)/V_(s)anomalies,a pattern that can be caused by overpressurized vapors due to high temperatures at these depths.Based on aftershock locations and velocity features,our studies support the conclusion that the 2017Pohang earthquake was triggered by injected EGS fluids that migrated into a blind fault.
基金This work was jointly supported by the National Key R&D Program of China(No.2021YFC3000700)the National Natural Science Foundation of China(No.42174066).
文摘The Yangbi M_(S)6.4 earthquake occurred on May 21,2021 in western Yunnan,China,where moderate earthquakes strike frequently.It exhibited a typical“foreshock-mainshock-aftershock”sequence and did not occur on a pre-existing active fault.The seismogenic environment and mechanism of this earthquake have aroused considerable research attention.In this study,we obtain the three-dimensional v_(P),v_(S)and v_(P)/v_(S)images using the v_(P)/v_(S)consistency-constrained double-difference tomography method,which improves the accuracy of v_(P)/v_(S)models.We focus on characteristics of v_(P)/v_(S)images in areas with a lateral resolution of 0.1°,and reveal the seismogenic environment of the Yangbi M_(S)6.4 earthquake.The conclusions are as follows:(1)Low velocity and high-v_(P)/v_(S)anomalies are revealed at different depths around the northern segment of the Red River fault.v_(S)and v_(P)/v_(S)images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature.(2)The source region of the Yangbi M_(S)6.4 earthquake is located in a low-v_(P)/v_(S)zone implying high medium strength.High-v_(P)/v_(S)anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts,which are unfavorable for stress accumulation and triggering large earthquakes.Such conditions have also prevented the earthquake sequence from extending northwestward.(3)With the southeastward extrusion of materials from the Tibetan Plateau,fluid migration was blocked by the low-v_(P)/v_(S)body in the source region.The high-v_(P)/v_(S)anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer,and preparing the largest foreshock in the transition zone of high to low v_(P)/v_(S).Meanwhile,tectonic stress incessantly accumulated in the brittle upper crust,eventually led to the M_(S)6.4 earthquake occurrence.
基金the National Natural Science Foun-dation of China(Grant Nos.41874052 and 41730212)the Guangdong Province Introduced Innovative R&D Team(Grant No.2017ZT072066)+2 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0701)the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311021002)the Guangdong Collaborative Innovation Center for Earthquake Prevention and Mitigation(Grant No.2018B020207011).
文摘The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as GHF and ZDF,respectively).Although the extension of the ZDF to the northeast,which represents the amalgamation of the two sub-blocks has been confirmed,the development of the GHF to the southwest remains to be verified.To better constrain the detailed deep structure beneath the southwest Cathaysia,which hold great significance for revealing the evolution of the SCB,a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin(SSB).Combining with the regional 10 permanent stations(PA),we obtained two profiles with teleseismic P-wave receiver function stacking.The most obvious feature in our results is the ascending Moho towards the coastal area,which is consistent with the passive margin continental and extensional tectonic setting.The stacking profile from the dense nodal array(DNA)shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB.We deduce that this offset may be casued by the deep extension of the GHF,which represents the remnants of the amalgamation of the Cathaysia block.From the other evidences,we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface.The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB.The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF,which serves as a channel for upwelling hot materials.
