A structural analysis was undertaken in the South Iceland Seismic Zone (SISZ) transform zone, and in the Hreppar Microplate (HMP) located between the propagating Eastern Rift Zone (ERZ) and the receding Western Rift Z...A structural analysis was undertaken in the South Iceland Seismic Zone (SISZ) transform zone, and in the Hreppar Microplate (HMP) located between the propagating Eastern Rift Zone (ERZ) and the receding Western Rift Zone (WRZ). The age of the oceanic crust in these areas is 3.4 Ma to present. About 20,000 fracture segments on aerial images reflect the dominance of NNE extensional structures in the WRZ. Around 9,000 basement faults, intrusions, secondary fractures, surface ruptures of earthquakes, and leakages were mapped in the outcrops of the HMP and the SISZ. About 23% of these fractures strike NNE, while 77% are dominantly northerly dextral and ENE sinistral, and secondarily E-W, WNW and NW sinistral strike- and oblique-slip structures, forming a Riedel shear pattern typical of a transform zone. Dyke injections into Riedel shears indicate a leaky transform zone. Fractures reactivated, accumulated slip, and re-opened for fluid flow. The ENE faults dip mostly to the southeast and could be the present boundary of the SISZ to the north. A 10 - 30 km wide ENE structural zone hosts a valley to the east, which could be deeper in the west. This ENE zone contains all the earthquakes, dominant ENE rivers, frequent ENE secondary fractures, and is likely the active part of the SISZ. The HMP does not show rotation since 3.4 Ma despite being between two rift segments. Future propagation/recession of the rift segments along their N55°E sections would cause a migration and a clockwise rotation of the SISZ from ENE to E-W. The boundary faults of the SISZ would then be E-W, with unchanged internal Riedel shears, compensating its sinistral motion. Insights into complexities of diverging plate boundaries are critical for resource management in such tectonic contexts.展开更多
The diverging plate boundaries in North Iceland and its shelf display a complex tectonic at the Kolbeinsey Ridge (K-R), the Northern Rift Zone (NRZ), and the Tj?rnes Fracture Zone containing the Grímsey Oblique R...The diverging plate boundaries in North Iceland and its shelf display a complex tectonic at the Kolbeinsey Ridge (K-R), the Northern Rift Zone (NRZ), and the Tj?rnes Fracture Zone containing the Grímsey Oblique Rift (GOR), the Húsavík-Flatey Fault (HFF), and the Dalvík Lineament (DL). While active deformation is well-known, the structural pattern is sporadically mapped and a comprehensive account of the upper Tertiary-present deformation is not fully at hand. To address the gaps, this paper provides new regional tectonic maps with continuous coverage, and detailed analyses of the deformation. Faults, open fractures, prominent joints and volcanic edifices were identified on Multibeam/Single beam, Spot 5, and Digital Elevation Model, and subjected to multidisciplinary structural analysis and correlation with selected data. Some of the results are: 1) Six sets constitute the structural pattern. The N-S rift-parallel normal faults are 1/3, and the shear fractures of the transform zone and the oblique rift 2/3 of the fracture population. The en échelon arrangements above deep-seated shear zones indicate dextral slip on WNW to NW, and sinistral slip on NNE to ENE faults, conformable with earthquake data. 2) During the polyphase tectonic, the six sets led to basin and horst formation, block compartmentalisation, rotation, horsetail splay, rhomb-graben in relay zone of strike-slips, and volcanism. 3) Listric faults are absent and the steeply-dipping faults are antithetic, synthetic, or form extensional flower structures above 4 km depth. The Plio-pleistocene/present syn-sedimentary deformation caused a deep half graben in the Eyjafjarearáll Basin (Ey), fault growth, rollover, and sediment onlaps, with some of the faults still active. 4) The plate boundaries of K-R/Ey, GOR/?xarfjreur/NRZ, and DL delimit a major microplate labelled here as Grímsey-Tj?rnes-Dalvík. 5) The WNW earthquake cluster in GOR corresponds either to a blind horsetail splay fault or to initiation of a transform segment parallel to the HFF. The described tectonic-sedimentary-magmatic deformation is relevant to other diverging plate boundaries where similar sets control the hydrocarbon and geothermal resources.展开更多
This paper presents a multidisciplinary structural analysis of a 165 km2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geother...This paper presents a multidisciplinary structural analysis of a 165 km2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geothermal field and its surroundings. About 10729 fracture segments (faults, open fractures, joints) are identified in the upper Tertiary to Holocene igneous series. The segments were extracted from aerial images and hillshade, and then analyzed in terms of number of sets, geometry, motions, frequency, and relative age. The correlation with surface geothermal manifestations, resistivity, earthquakes, and occasional well data reveals the critical regional and local fractures at the surface, reservoir level and greater depth. The main conclusions of this study are: 1) The structural pattern consists of N-S rift-parallel extensional fractures and the Riedel shears of the transform zone striking NNE, ENE, E-W, WNW and NW, which compartmentalize together the blocks at any scale. 2) The en échelon segmentation shows strike and oblique slips on the Riedel shears, with a dextral component on the WNW and NW planes and a sinistral component on the NNE to ENE faults. 3) Fractures form under the influence of the transform mechanism and the effect of rifting becomes significant only with time. 4) The WNW dextral oblique-slip Stórihver Fault of the transform zone has a horsetail splay that extends eastwards into the geothermal field. There, this structure, along with few NW, ENE, NNE and N-S fractures, controls the alteration, alignment of fumaroles, emanating deep gases. These fractures also rupture during natural or induced earthquakes. 5) The resistivity anomalies present en échelon geometries controlled by the six fracture sets. These anomalies display clockwise and anticlockwise rotations within the upper 8 km crustal depth, but at 8 km depth, only three sets (the N-S rift structures, and the E-W and the NW Riedel shears) are present at the rift and transform plate boundaries. Results of this study are relevant to resource exploration in other complex extensional contexts where rift and transform interact.ööö展开更多
A theoretical model that takes into account the flee-volume aided cooperative shearing of shear transformation zones （STZs） is developed to quantitatively understand the ductile-to-brittle transition （DBT） of meta...A theoretical model that takes into account the flee-volume aided cooperative shearing of shear transformation zones （STZs） is developed to quantitatively understand the ductile-to-brittle transition （DBT） of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-tvpe rearrangements to dilatational processes （termed tension transformation zones （TrZs））.展开更多
The continuous cooling transformation curve of heat-affected zone （HAZ） of X70 pipeline steel was mea- sured by Gleeble-3500 thermal mechanical simulator, optical microscope （OM） and hardness analysis. The microst...The continuous cooling transformation curve of heat-affected zone （HAZ） of X70 pipeline steel was mea- sured by Gleeble-3500 thermal mechanical simulator, optical microscope （OM） and hardness analysis. The microstructure transformation rule at different cooling rates and solution behaviors of microalloy carbonitride during heating process of simulated specimens were investigated. When the cooling rate changes from 10 to 20 ℃.s-l, microstructures at HAZ are identified as granular bainite, lathy bainite, and quasi-polygonal ferrite. This micro- structure is featured with fine ferrite grains, martensite/ austenite islands dispersed, high-density dislocations, and fine carbonitride particles, resulting in improving the strength and toughness of HAZ. With the cooling rate increasing to above 40 ℃.s-1, the microstructure is pre- dominantly coarse lathy bainite with clear primary aus- tenite grain boundary. While the cooling rate decreases to below 1 ℃.s-1, a fairly small amount of pearlite can be observed at the boundaries. The strength and toughness of HAZ are deteriorated because of coarse grains among these microstructures. Most of microalloy carbonitrides in HAZ could be dissolved in the matrix during heating process. A few of TiN particles existing as residues in the matrix can prevent austenite grain from growing, and then improve the strength and toughness of HAZ.展开更多
The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformati...The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime.At relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base metal.When the cooling rate was below 9C/s,the welding HAZ would have an obvious softening.The analysis of transformation rates in continuous cooling processes was completed by numerical differential method.The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.展开更多
The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary condition...The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary conditions. With wave breaking and energy dissipation expressed in a direct form in the equation, the proposed model could provide an efficient numerical scheme and accurate predictions of wave transformation across the surf zone. The radiation boundary conditions are iterated in the model without use of approximations. The numerical predictions for wave height distributions across the surf zone are compared with experimental data over typical beach profiles. In addition, tests of waves scattering around a circular pile show that the proposed model could also provide reasonable improvement on the radiation boundary conditions for large incident angles of waves.展开更多
城市功能区识别可为城市建设决策提供技术支撑。本研究提出了面向城市功能区识别的多源场景特征Transformer融合方法。利用路网构建交通分析区(Traffic Analysis Zone,TAZ),采用Delaunay三角网创建POI(Point of Interest)数据的图结构,...城市功能区识别可为城市建设决策提供技术支撑。本研究提出了面向城市功能区识别的多源场景特征Transformer融合方法。利用路网构建交通分析区(Traffic Analysis Zone,TAZ),采用Delaunay三角网创建POI(Point of Interest)数据的图结构,通过TAZ获得遥感数据的影像对象;利用图卷积网络提取POI图结构的社会场景特征,由ResNet-50编码遥感数据的自然场景特征;基于Transformer的多头注意力机制融合多维特征,依托SoftMax实现功能区识别。以沈阳市主城区为例,以2021年的OpenStreetMap、POI和遥感数据为数据源。该方法的总体精度和Kappa系数为82.2%和70%,Kappa系数较单一数据方法和其他融合方法至少提高18%和9%。本研究采用Transformer融合社会场景特征和自然场景特征,解决了多源数据难以集成表达的问题,为城市功能区识别提供了新的技术路径。展开更多
Collecting waste water with a certain c onc entration of organic pollutants COD (chemical oxygen demand), static adsorption, static biodegradation and dynamic soil column experiments were made in laborato ry, we rese...Collecting waste water with a certain c onc entration of organic pollutants COD (chemical oxygen demand), static adsorption, static biodegradation and dynamic soil column experiments were made in laborato ry, we researched migration and transformation of COD in aerated zone, and put f orward a mathematical model showing the process. The results show that adsorptio n of organism in aerated zone is linear, which is represented by Henry's law s =K dc+s d, adsorption coefficient K d=0.069 3; biodegradati on diagram accord basically with first order kinetics equation c=c 0e -K 1t , biodegradation coefficient K 1 = 0.049 9 d -1 ; dispersio n coefficient D= 0.002 42 m 2/d in experiments. The migration and transform ation of organic pollutants (COD) in aerated zone jointly result from many f actors such as dispersion, adsorption and biodegradation etc..展开更多
Following a quasi-dynamic scheme proposed by Minear and Toksoz (1970), thermal structures of subduction zonesfor different models by finite element method (FEM) were calculated. Density distribution and p-wave anomaly...Following a quasi-dynamic scheme proposed by Minear and Toksoz (1970), thermal structures of subduction zonesfor different models by finite element method (FEM) were calculated. Density distribution and p-wave anomaly ofsubduction zones were calculated at the same time. Comparing with seismological evidences and results of laboratories. it is proposed that earthquakes occurred below 400 km depth are probably controlled by anti-crackmechanism.展开更多
The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to unde...The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to understand phase transformations of relevant mantle minerals under the high-temperature and high-pressure circumstance of the Earth's interior.In this study,we detect the X-discontinuity beneath the Ryukyu subduction zone using five intermediate-depth events recorded by the dense Alaska Regional Network(AK).The X-discontinuity is successfully revealed from the robust slant stacking of the secondary down-going and converting Sd P phases.From the depth distribution of conversion points,we find that the X-discontinuity's depth ranges between 269 km and 313 km,with an average depth of 295 km.All the conversion points are located beneath the down-dipping side of the Philippine Sea slab.From energy comparisons in vespagrams for observed and synthetic seismograms,the strong converted energy is more likely from a thin high-velocity layer,and the S-wave velocity jumps across the X-discontinuity are up to 5% to 8% with an average of 6.0%.According to previous petrological and seismological studies,the X-discontinuity we detected can be interpreted as the phase transformation of coesite to stishovite in eclogitic materials within the oceanic crust.展开更多
文摘A structural analysis was undertaken in the South Iceland Seismic Zone (SISZ) transform zone, and in the Hreppar Microplate (HMP) located between the propagating Eastern Rift Zone (ERZ) and the receding Western Rift Zone (WRZ). The age of the oceanic crust in these areas is 3.4 Ma to present. About 20,000 fracture segments on aerial images reflect the dominance of NNE extensional structures in the WRZ. Around 9,000 basement faults, intrusions, secondary fractures, surface ruptures of earthquakes, and leakages were mapped in the outcrops of the HMP and the SISZ. About 23% of these fractures strike NNE, while 77% are dominantly northerly dextral and ENE sinistral, and secondarily E-W, WNW and NW sinistral strike- and oblique-slip structures, forming a Riedel shear pattern typical of a transform zone. Dyke injections into Riedel shears indicate a leaky transform zone. Fractures reactivated, accumulated slip, and re-opened for fluid flow. The ENE faults dip mostly to the southeast and could be the present boundary of the SISZ to the north. A 10 - 30 km wide ENE structural zone hosts a valley to the east, which could be deeper in the west. This ENE zone contains all the earthquakes, dominant ENE rivers, frequent ENE secondary fractures, and is likely the active part of the SISZ. The HMP does not show rotation since 3.4 Ma despite being between two rift segments. Future propagation/recession of the rift segments along their N55°E sections would cause a migration and a clockwise rotation of the SISZ from ENE to E-W. The boundary faults of the SISZ would then be E-W, with unchanged internal Riedel shears, compensating its sinistral motion. Insights into complexities of diverging plate boundaries are critical for resource management in such tectonic contexts.
文摘The diverging plate boundaries in North Iceland and its shelf display a complex tectonic at the Kolbeinsey Ridge (K-R), the Northern Rift Zone (NRZ), and the Tj?rnes Fracture Zone containing the Grímsey Oblique Rift (GOR), the Húsavík-Flatey Fault (HFF), and the Dalvík Lineament (DL). While active deformation is well-known, the structural pattern is sporadically mapped and a comprehensive account of the upper Tertiary-present deformation is not fully at hand. To address the gaps, this paper provides new regional tectonic maps with continuous coverage, and detailed analyses of the deformation. Faults, open fractures, prominent joints and volcanic edifices were identified on Multibeam/Single beam, Spot 5, and Digital Elevation Model, and subjected to multidisciplinary structural analysis and correlation with selected data. Some of the results are: 1) Six sets constitute the structural pattern. The N-S rift-parallel normal faults are 1/3, and the shear fractures of the transform zone and the oblique rift 2/3 of the fracture population. The en échelon arrangements above deep-seated shear zones indicate dextral slip on WNW to NW, and sinistral slip on NNE to ENE faults, conformable with earthquake data. 2) During the polyphase tectonic, the six sets led to basin and horst formation, block compartmentalisation, rotation, horsetail splay, rhomb-graben in relay zone of strike-slips, and volcanism. 3) Listric faults are absent and the steeply-dipping faults are antithetic, synthetic, or form extensional flower structures above 4 km depth. The Plio-pleistocene/present syn-sedimentary deformation caused a deep half graben in the Eyjafjarearáll Basin (Ey), fault growth, rollover, and sediment onlaps, with some of the faults still active. 4) The plate boundaries of K-R/Ey, GOR/?xarfjreur/NRZ, and DL delimit a major microplate labelled here as Grímsey-Tj?rnes-Dalvík. 5) The WNW earthquake cluster in GOR corresponds either to a blind horsetail splay fault or to initiation of a transform segment parallel to the HFF. The described tectonic-sedimentary-magmatic deformation is relevant to other diverging plate boundaries where similar sets control the hydrocarbon and geothermal resources.
文摘This paper presents a multidisciplinary structural analysis of a 165 km2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geothermal field and its surroundings. About 10729 fracture segments (faults, open fractures, joints) are identified in the upper Tertiary to Holocene igneous series. The segments were extracted from aerial images and hillshade, and then analyzed in terms of number of sets, geometry, motions, frequency, and relative age. The correlation with surface geothermal manifestations, resistivity, earthquakes, and occasional well data reveals the critical regional and local fractures at the surface, reservoir level and greater depth. The main conclusions of this study are: 1) The structural pattern consists of N-S rift-parallel extensional fractures and the Riedel shears of the transform zone striking NNE, ENE, E-W, WNW and NW, which compartmentalize together the blocks at any scale. 2) The en échelon segmentation shows strike and oblique slips on the Riedel shears, with a dextral component on the WNW and NW planes and a sinistral component on the NNE to ENE faults. 3) Fractures form under the influence of the transform mechanism and the effect of rifting becomes significant only with time. 4) The WNW dextral oblique-slip Stórihver Fault of the transform zone has a horsetail splay that extends eastwards into the geothermal field. There, this structure, along with few NW, ENE, NNE and N-S fractures, controls the alteration, alignment of fumaroles, emanating deep gases. These fractures also rupture during natural or induced earthquakes. 5) The resistivity anomalies present en échelon geometries controlled by the six fracture sets. These anomalies display clockwise and anticlockwise rotations within the upper 8 km crustal depth, but at 8 km depth, only three sets (the N-S rift structures, and the E-W and the NW Riedel shears) are present at the rift and transform plate boundaries. Results of this study are relevant to resource exploration in other complex extensional contexts where rift and transform interact.ööö
基金supported by the National Nature Science Foundation of China (Grant Nos.11522221,11372315,11472287,and 51171138)the National Basic Research Program of China (Grant No.2012CB937500)+1 种基金the CAS/SAFEA International Partnership Program for Creative Research Teamspartially also by DFG
文摘A theoretical model that takes into account the flee-volume aided cooperative shearing of shear transformation zones （STZs） is developed to quantitatively understand the ductile-to-brittle transition （DBT） of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-tvpe rearrangements to dilatational processes （termed tension transformation zones （TrZs））.
基金financially supported by the National Natural Science Foundation of China(No.51274083)the Natural Science Foundation of Hebei Province(No.E2013209228)+1 种基金the Innovation Team Leading Talent in Universities Cultivation Plan of Hebei Province(No.LJRC007)the Science and Technology Project of Tangshan City(No.131302108b)
文摘The continuous cooling transformation curve of heat-affected zone （HAZ） of X70 pipeline steel was mea- sured by Gleeble-3500 thermal mechanical simulator, optical microscope （OM） and hardness analysis. The microstructure transformation rule at different cooling rates and solution behaviors of microalloy carbonitride during heating process of simulated specimens were investigated. When the cooling rate changes from 10 to 20 ℃.s-l, microstructures at HAZ are identified as granular bainite, lathy bainite, and quasi-polygonal ferrite. This micro- structure is featured with fine ferrite grains, martensite/ austenite islands dispersed, high-density dislocations, and fine carbonitride particles, resulting in improving the strength and toughness of HAZ. With the cooling rate increasing to above 40 ℃.s-1, the microstructure is pre- dominantly coarse lathy bainite with clear primary aus- tenite grain boundary. While the cooling rate decreases to below 1 ℃.s-1, a fairly small amount of pearlite can be observed at the boundaries. The strength and toughness of HAZ are deteriorated because of coarse grains among these microstructures. Most of microalloy carbonitrides in HAZ could be dissolved in the matrix during heating process. A few of TiN particles existing as residues in the matrix can prevent austenite grain from growing, and then improve the strength and toughness of HAZ.
文摘The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime.At relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base metal.When the cooling rate was below 9C/s,the welding HAZ would have an obvious softening.The analysis of transformation rates in continuous cooling processes was completed by numerical differential method.The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.
基金This research is supported by the National Science Council of Taiwan under the grant of NSC 86-2611-E-006-019.
文摘The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary conditions. With wave breaking and energy dissipation expressed in a direct form in the equation, the proposed model could provide an efficient numerical scheme and accurate predictions of wave transformation across the surf zone. The radiation boundary conditions are iterated in the model without use of approximations. The numerical predictions for wave height distributions across the surf zone are compared with experimental data over typical beach profiles. In addition, tests of waves scattering around a circular pile show that the proposed model could also provide reasonable improvement on the radiation boundary conditions for large incident angles of waves.
文摘城市功能区识别可为城市建设决策提供技术支撑。本研究提出了面向城市功能区识别的多源场景特征Transformer融合方法。利用路网构建交通分析区(Traffic Analysis Zone,TAZ),采用Delaunay三角网创建POI(Point of Interest)数据的图结构,通过TAZ获得遥感数据的影像对象;利用图卷积网络提取POI图结构的社会场景特征,由ResNet-50编码遥感数据的自然场景特征;基于Transformer的多头注意力机制融合多维特征,依托SoftMax实现功能区识别。以沈阳市主城区为例,以2021年的OpenStreetMap、POI和遥感数据为数据源。该方法的总体精度和Kappa系数为82.2%和70%,Kappa系数较单一数据方法和其他融合方法至少提高18%和9%。本研究采用Transformer融合社会场景特征和自然场景特征,解决了多源数据难以集成表达的问题,为城市功能区识别提供了新的技术路径。
文摘Collecting waste water with a certain c onc entration of organic pollutants COD (chemical oxygen demand), static adsorption, static biodegradation and dynamic soil column experiments were made in laborato ry, we researched migration and transformation of COD in aerated zone, and put f orward a mathematical model showing the process. The results show that adsorptio n of organism in aerated zone is linear, which is represented by Henry's law s =K dc+s d, adsorption coefficient K d=0.069 3; biodegradati on diagram accord basically with first order kinetics equation c=c 0e -K 1t , biodegradation coefficient K 1 = 0.049 9 d -1 ; dispersio n coefficient D= 0.002 42 m 2/d in experiments. The migration and transform ation of organic pollutants (COD) in aerated zone jointly result from many f actors such as dispersion, adsorption and biodegradation etc..
文摘Following a quasi-dynamic scheme proposed by Minear and Toksoz (1970), thermal structures of subduction zonesfor different models by finite element method (FEM) were calculated. Density distribution and p-wave anomaly ofsubduction zones were calculated at the same time. Comparing with seismological evidences and results of laboratories. it is proposed that earthquakes occurred below 400 km depth are probably controlled by anti-crackmechanism.
基金supported by the China Postdoctoral Science Foundation(119103S282)National Natural Science Foundation of China(41704090,41474040 and 41504050)
文摘The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to understand phase transformations of relevant mantle minerals under the high-temperature and high-pressure circumstance of the Earth's interior.In this study,we detect the X-discontinuity beneath the Ryukyu subduction zone using five intermediate-depth events recorded by the dense Alaska Regional Network(AK).The X-discontinuity is successfully revealed from the robust slant stacking of the secondary down-going and converting Sd P phases.From the depth distribution of conversion points,we find that the X-discontinuity's depth ranges between 269 km and 313 km,with an average depth of 295 km.All the conversion points are located beneath the down-dipping side of the Philippine Sea slab.From energy comparisons in vespagrams for observed and synthetic seismograms,the strong converted energy is more likely from a thin high-velocity layer,and the S-wave velocity jumps across the X-discontinuity are up to 5% to 8% with an average of 6.0%.According to previous petrological and seismological studies,the X-discontinuity we detected can be interpreted as the phase transformation of coesite to stishovite in eclogitic materials within the oceanic crust.
