The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Tianyu Zheng - One of the best experts on this subject based on the ideXlab platform.
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geographic Boundary and shear wave velocity structure of the pacific anomaly near the core mantle Boundary beneath western pacific
Earth and Planetary Science Letters, 2006Co-Authors: Yumei He, Tianyu ZhengAbstract:We determine the Geographical Boundary and shear-velocity structure of a very-low velocity province at the base of the Earth's mantle beneath western Pacific (we term it the “Pacific anomaly”) based on the waveform modeling and travel time analysis of ScSH–SH phases. Our seismic data are from the China National Digital Seismographic Network, the F-net in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScS–SH differential travel-time residuals allow the northwestern geographic Boundary of the anomaly to be clearly defined. The seismic data also suggest that the average shearvelocity reduction inside the anomaly reaches �5% in the lowermost 300km of the mantle. Waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern Boundary is best characterized by a shear-velocity model with a velocity jump of about 2% at about 100–145km above the core–mantle Boundary and a thin (30-km thick) basal layer with a shear wave velocity reduction of �13%. Stacked seismic data sampling the middle of the anomaly, however, show no evidence for any internal discontinuity with a velocity decrease greater than �2% in the middle of the anomaly. Overall, the seismic data sampling the base of the “Pacific anomaly” can be explained by a negative shear-velocity gradient from 0% to �1% (top) to �13% (bottom) in the lowermost 220 km of the mantle, similar to those of a very-low velocity province beneath the South Atlantic Ocean and the Indian Ocean. Such a strong negative shear-velocity gradient can be explained by partial melting of a compositional anomaly produced early in the Earth's history located within a bottom thermal Boundary layer. Our travel time data also exhibit small-scale variations inside the anomaly, indicating existence of internal small-scale seismic heterogeneities inside the “Pacific anomaly”.
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Geographic Boundary and shear wave velocity structure of the “Pacific anomaly” near the core–mantle Boundary beneath western Pacific
Earth and Planetary Science Letters, 2006Co-Authors: Lianxing Wen, Tianyu ZhengAbstract:We determine the Geographical Boundary and shear-velocity structure of a very-low velocity province at the base of the Earth's mantle beneath western Pacific (we term it the “Pacific anomaly”) based on the waveform modeling and travel time analysis of ScSH–SH phases. Our seismic data are from the China National Digital Seismographic Network, the F-net in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScS–SH differential travel-time residuals allow the northwestern geographic Boundary of the anomaly to be clearly defined. The seismic data also suggest that the average shearvelocity reduction inside the anomaly reaches �5% in the lowermost 300km of the mantle. Waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern Boundary is best characterized by a shear-velocity model with a velocity jump of about 2% at about 100–145km above the core–mantle Boundary and a thin (30-km thick) basal layer with a shear wave velocity reduction of �13%. Stacked seismic data sampling the middle of the anomaly, however, show no evidence for any internal discontinuity with a velocity decrease greater than �2% in the middle of the anomaly. Overall, the seismic data sampling the base of the “Pacific anomaly” can be explained by a negative shear-velocity gradient from 0% to �1% (top) to �13% (bottom) in the lowermost 220 km of the mantle, similar to those of a very-low velocity province beneath the South Atlantic Ocean and the Indian Ocean. Such a strong negative shear-velocity gradient can be explained by partial melting of a compositional anomaly produced early in the Earth's history located within a bottom thermal Boundary layer. Our travel time data also exhibit small-scale variations inside the anomaly, indicating existence of internal small-scale seismic heterogeneities inside the “Pacific anomaly”.
Lianxing Wen - One of the best experts on this subject based on the ideXlab platform.
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Geographic Boundary of the “Pacific Anomaly” and its geometry and transitional structure in the north
Journal of Geophysical Research: Solid Earth, 2012Co-Authors: Lianxing WenAbstract:[1] We determine the Geographical Boundary and average shear velocity structure of the Pacific Anomaly at the base of the mantle based on travel time analysis of ScSH-SH and ScS2 (ScSScS)-SS phases and waveform modeling results. We further constrain the detailed geometry of the northern Anomaly around (20°N, −170°E) and its transition to the surrounding high velocity region along three perpendicular cross sections on the basis of forward waveform modeling of the observed direct S and ScS phases. The observed differential travel-time residuals and waveform modeling results allow the whole geographic Boundary of the Anomaly to be delineated and the area of the base of the Anomaly is estimated to be 1.9 × 107 km2. The maximum shear velocity perturbation inside the Anomaly reaches −5% in the lowermost 500 km of the mantle. Waveform analysis suggests that the northern Anomaly reaches 450 km above the CMB with both steeply and shallowly dipping edges and its basal layer extends beneath the surrounding mantle with the degree of extension changing rapidly across a small distance. The inferred characteristics of the Anomaly support the previous suggestion that the Pacific Anomaly represents a chemical anomaly. However, unlike the inferred features of the African Anomaly pointing to an ancient compositionally distinct and geologically stable anomaly, the existence of several separated piles extending into the mid-lower mantle, the complex morphology of the piles with both steeply and shallowly dipping edges and the presence of many ultra-low velocity zones at its base suggest that the Pacific Anomaly likely possesses varying intrinsic compositions and exhibits complex interaction with the surrounding mantle.
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Geographic Boundary and shear wave velocity structure of the “Pacific anomaly” near the core–mantle Boundary beneath western Pacific
Earth and Planetary Science Letters, 2006Co-Authors: Lianxing Wen, Tianyu ZhengAbstract:We determine the Geographical Boundary and shear-velocity structure of a very-low velocity province at the base of the Earth's mantle beneath western Pacific (we term it the “Pacific anomaly”) based on the waveform modeling and travel time analysis of ScSH–SH phases. Our seismic data are from the China National Digital Seismographic Network, the F-net in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScS–SH differential travel-time residuals allow the northwestern geographic Boundary of the anomaly to be clearly defined. The seismic data also suggest that the average shearvelocity reduction inside the anomaly reaches �5% in the lowermost 300km of the mantle. Waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern Boundary is best characterized by a shear-velocity model with a velocity jump of about 2% at about 100–145km above the core–mantle Boundary and a thin (30-km thick) basal layer with a shear wave velocity reduction of �13%. Stacked seismic data sampling the middle of the anomaly, however, show no evidence for any internal discontinuity with a velocity decrease greater than �2% in the middle of the anomaly. Overall, the seismic data sampling the base of the “Pacific anomaly” can be explained by a negative shear-velocity gradient from 0% to �1% (top) to �13% (bottom) in the lowermost 220 km of the mantle, similar to those of a very-low velocity province beneath the South Atlantic Ocean and the Indian Ocean. Such a strong negative shear-velocity gradient can be explained by partial melting of a compositional anomaly produced early in the Earth's history located within a bottom thermal Boundary layer. Our travel time data also exhibit small-scale variations inside the anomaly, indicating existence of internal small-scale seismic heterogeneities inside the “Pacific anomaly”.
Yumei He - One of the best experts on this subject based on the ideXlab platform.
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geographic Boundary and shear wave velocity structure of the pacific anomaly near the core mantle Boundary beneath western pacific
Earth and Planetary Science Letters, 2006Co-Authors: Yumei He, Tianyu ZhengAbstract:We determine the Geographical Boundary and shear-velocity structure of a very-low velocity province at the base of the Earth's mantle beneath western Pacific (we term it the “Pacific anomaly”) based on the waveform modeling and travel time analysis of ScSH–SH phases. Our seismic data are from the China National Digital Seismographic Network, the F-net in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScS–SH differential travel-time residuals allow the northwestern geographic Boundary of the anomaly to be clearly defined. The seismic data also suggest that the average shearvelocity reduction inside the anomaly reaches �5% in the lowermost 300km of the mantle. Waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern Boundary is best characterized by a shear-velocity model with a velocity jump of about 2% at about 100–145km above the core–mantle Boundary and a thin (30-km thick) basal layer with a shear wave velocity reduction of �13%. Stacked seismic data sampling the middle of the anomaly, however, show no evidence for any internal discontinuity with a velocity decrease greater than �2% in the middle of the anomaly. Overall, the seismic data sampling the base of the “Pacific anomaly” can be explained by a negative shear-velocity gradient from 0% to �1% (top) to �13% (bottom) in the lowermost 220 km of the mantle, similar to those of a very-low velocity province beneath the South Atlantic Ocean and the Indian Ocean. Such a strong negative shear-velocity gradient can be explained by partial melting of a compositional anomaly produced early in the Earth's history located within a bottom thermal Boundary layer. Our travel time data also exhibit small-scale variations inside the anomaly, indicating existence of internal small-scale seismic heterogeneities inside the “Pacific anomaly”.
Paul R Renne - One of the best experts on this subject based on the ideXlab platform.
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temporal spatial evolution of low sio2 volcanism in the pleistocene west eifel volcanic field west germany and relationship to upwelling asthenosphere
Journal of Geodynamics, 2015Co-Authors: Dieter F Mertz, Werner Lohnertz, Sebastien Nomade, Alison Pereira, Dejan Prelevic, Paul R RenneAbstract:Abstract The temporal–spatial evolution of low-SiO 2 lavas from the Pleistocene West Eifel volcanic field (Central European Volcanic Province) and linked petrogenetic variations are evaluated using 40 Ar/ 39 Ar age and geochemical data. Geochronological and petrological evidence is related to the physical structure of the previously established seismologically anomalous asthenosphere interpreted as thermally upwelling mantle (Eifel Plume). Lava flows >480 ka (Middle Pleistocene) occur exclusively in the NW of the volcanic field. After a time span of ca. 400 ka lacking significant activity, volcanism has migrated to the SE generating flows At melting depth >70 km of parental asthenospheric melts in garnet–spinel peridotite the surface-projected contour of the low-velocity P -wave anomaly coincides with the Geographical Boundary separating >480 ka volcanism in the NW from 480 ka volcanism reside within and beyond the P -wave velocity anomaly, respectively. The coupling between time-space pattern of volcanism and seismological contrast in the mantle sources indicates that volcanic activity is linked to a highly dynamic low-velocity anomaly with lateral and vertical motion rates of 4–5 cm/year and up to 6 cm/year, respectively. The change in seismological contrast is accompanied by a transition in the petrogenetic style resulting from differently intense thermal erosion of multiply metasomatized lithosphere by upwelling asthenosphere. Asthenosphere-lithosphere interaction is widespread in the NW and subordinate in the SE of the volcanic field, where melts ascended through a more refractory lithosphere which has been affected by preferential melting of hydrous portions by pre-80 ka thermal exposure.
Ke Guo - One of the best experts on this subject based on the ideXlab platform.
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Geographical Boundary and climatic analysis of Pinus tabulaeformis in China: Insights on its afforestation
Ecological Engineering, 2016Co-Authors: Ke GuoAbstract:Abstract Pinus tabulaeformis , as an endemic species in China, is one of the main tree species for afforestation. For rational cultivation planning and conservation, it is necessary to understand the Geographical boundaries and the ecological characteristics of P. tabulaeformis , and to explore its priority afforestation areas. In this study, maximum entropy modeling (MaxEnt) was used to identify and prioritize suitable habitats of P. tabulaeformis , based on 13 climatic variables and GlobCover 2009 data. The results show that the MaxEnt model performs better than random prediction, with an average test area under the curve (AUC) value of 0.93 (0.91–0.94). Precipitation of wettest month (PWM), annual biotemperature (ABT), mean temperature of the coldest month (MTCM), annual mean temperature (AMT), precipitation of driest month (PDM), coldness index (CI), annual precipitation (AP), and mean temperature of the warmest month (MTWM) are identified as dominant variables which explain 94.6% of variability the Geographical distribution of P. tabulaeformis . Climatic conditions of P. tabulaeformis in the core area of its distribution are as follows: PWM, 100–246 mm; ABT, 3.0–4.7 °C; MTCM, −20.2 to −1.1 °C; AMT, 2.9–14.7 °C; PDM, 2–11 mm; CI, −49.4–0 °C; AP, 431–1122 mm; and MTWM, 19.6–31.2 °C. The suitable areas for afforestation are 2.6 × 10 4 km 2 (patches with an area >1 km 2 ), 1.6 × 10 4 km 2 (patches with an area >10 km 2 ), and 1.2 × 10 4 km 2 (patches with an area >100 km 2 ), which are mainly located in north Shaanxi, south Ningxia, and the middle of Gansu and Liaoning provinces with serious landscape fragmentation caused by human agricultural activities. Our simulation results can improve our understanding of the Geographical and ecological characteristics of P. tabulaeformis and provide prediction of priority areas for afforestation of this species under current and future climate change scenarios in China.