The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source S...The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source SdP sampling from a large global dataset,we image topographies of transition zone discontinuities such as the 410-km and 660-km discontinuities(410 and 660)beneath the Kamchatka and conduct cross-section comparisons with the seismicity.Compared with the IASP91 model,the 410 exhibits apparent uplifts of 45-65 km with an average of 55 km in a horizontal width of~130 km,corresponding to lowtemperature anomalies of 750-1083 K with an average of 916 K.In contrast,the 660 shows depressions of 15-37 km with an average of 25 km together with downward deflections in a width of~260 km,implying low-temperature anomalies of 161-397 K with an average of 268 K.Thus,we confirm a thickened MTZ with a thickness of 325-345 km around the cold descending Pacific slab.We suggest that topographic patterns of transition zone discontinuities imply a Pacific slab that has been significantly heated in the MTZ with broadened thermal effects on the 660.When considered along with other studies,we infer that the slab is possibly heated by hot mantle flows around the torn slab window extended to at least the MTZ range,thus inducing variations in thermal and rheological properties of the slab.Our seismic results can provide more insight into slab dynamics in the northwestern Pacific.展开更多
Digital waveform data recorded by the vertical component short period stations at the American networks of SCSN, NCSN and PNSN and three components broadband stations at the Germany and Swiss networks and arrays of GR...Digital waveform data recorded by the vertical component short period stations at the American networks of SCSN, NCSN and PNSN and three components broadband stations at the Germany and Swiss networks and arrays of GRFN, GRSN and SDSNet for the events between 1981 and 2000 under Izu-Bonin are used as data sets. The N-th root slant stack method was used to pick up the SdP phase converted at the velocity interface beneath source and the regionalized difference of the 660 km discontinuity beneath Izu-Bonin is studied. It is found that while the dip angles of the subducting slab and the maximal depths of sources increase gradually from 35N to 26N, the 660 km discontinuity appears regionalized differences. The discontinuity exists at 660 km while there is no effect from subducting slab, but it is depressed to the depth of 720 km while there are obvious effects. The dispersion of converted points is still an unsolved problem which maybe result from the complex structure of the discontinuity, converted phases which were misjudged, or the assumption of one dimensional spherical earth model.展开更多
Upper mantle discontinuities play an important role in slab dynamics and mantle responses in the subduction zones.Despite increasing numbers of seismological observations in the Hindu Kush, fine structures of mantle d...Upper mantle discontinuities play an important role in slab dynamics and mantle responses in the subduction zones.Despite increasing numbers of seismological observations in the Hindu Kush, fine structures of mantle discontinuities still remain less explored, highlighting less understood interactions of the Indian slab and discontinuities. Here we collected a large dataset of several dense seismic networks/arrays, extracted near-source SdP waves in P-wave codas using the N-th root slant stackings, and then systematically imaged upper mantle discontinuities around the Indian slab beneath Hindu Kush. In comparison with the IASP91 model, we confirmed an abrupt topographic transition of the 410-km discontinuity(410) from uplifts of up to 41 km to depressions of less than 20 km near the slab edge and a slightly depressed 660-km discontinuity(660) with depths of 660 to 668 km below the slab front, as well as a fluctuating 300-km discontinuity(300) with depths of 264 to 337 km. We suggest that the 410 is elevated by the Indian slab due to the interior coldness, and deepened near the slab edge by the hot upwelling slab-entrained mantle that escapes below the slab bottom. Based on a depressed 410 inside the Indian slab and a 660with slight depressions below the slab, we infer that the subducted Indian slab currently stretches into the upper MTZ. Moreover,we interpret the fluctuant 300 as the coesite to stishovite phase transition in the subduction-zone mantle enriched in the eclogite.When considered alongside other studies, our results can provide more insights into the dynamics of the Indian slab and mantle responses.展开更多
The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth r...The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth root slant stack and digital records from networks in Germany and the western United States. Results show the obvious evidence for reflected and refractive phases associated with the 410 km and 660 km discontinuities. There may be discontinuities at other depths such as 150 km, 220 km and 520 km. The 410 km discontinuity is elevated and the 660 km discontinuity is depressed respectively, consistent with the expected thermal signature of the phase transitions. The subducting slab has penetrated into the lower mantle in the northern part of the Sea of Okhotsk, while it is stagnant on the 660 km discontinuity in the southern part.展开更多
The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath I...The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath Izu-Bonin and Japan Sea. The mantle discontinuities and the effects of subducting slab on the 660 km and 410 km discontinuities are studied. It is found that there are mantle discontinuities existing at the depths of 170, 220, 300, 410, 660, 850 and 1150 km. Beneath Izu-Bonin, the 410 km discontinuity is elevated, while the 660 km discontinuity is depressed; for both discontinuities, there are regionalized differences. Beneath Japan Sea, however, there is no depth variation of the 410 km discontinuity, and the 660 km discontinuity is depressed without obvious effect of the subducting slab.展开更多
基金supported by the Central Public-interest Scientific Institution Basal Research Fund(No.CEAIEF 20220201)the National Natural Science Foundation of China(Nos.42374113 and 42074101)the Central Publicinterest Scientific Institution Basal Research Fund(No.CEAIEF20230204).
文摘The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source SdP sampling from a large global dataset,we image topographies of transition zone discontinuities such as the 410-km and 660-km discontinuities(410 and 660)beneath the Kamchatka and conduct cross-section comparisons with the seismicity.Compared with the IASP91 model,the 410 exhibits apparent uplifts of 45-65 km with an average of 55 km in a horizontal width of~130 km,corresponding to lowtemperature anomalies of 750-1083 K with an average of 916 K.In contrast,the 660 shows depressions of 15-37 km with an average of 25 km together with downward deflections in a width of~260 km,implying low-temperature anomalies of 161-397 K with an average of 268 K.Thus,we confirm a thickened MTZ with a thickness of 325-345 km around the cold descending Pacific slab.We suggest that topographic patterns of transition zone discontinuities imply a Pacific slab that has been significantly heated in the MTZ with broadened thermal effects on the 660.When considered along with other studies,we infer that the slab is possibly heated by hot mantle flows around the torn slab window extended to at least the MTZ range,thus inducing variations in thermal and rheological properties of the slab.Our seismic results can provide more insight into slab dynamics in the northwestern Pacific.
基金State Natural Science Foundation of China (49874020) and the Special Funds for Major State Basic Research of China (95-13-04-06).
文摘Digital waveform data recorded by the vertical component short period stations at the American networks of SCSN, NCSN and PNSN and three components broadband stations at the Germany and Swiss networks and arrays of GRFN, GRSN and SDSNet for the events between 1981 and 2000 under Izu-Bonin are used as data sets. The N-th root slant stack method was used to pick up the SdP phase converted at the velocity interface beneath source and the regionalized difference of the 660 km discontinuity beneath Izu-Bonin is studied. It is found that while the dip angles of the subducting slab and the maximal depths of sources increase gradually from 35N to 26N, the 660 km discontinuity appears regionalized differences. The discontinuity exists at 660 km while there is no effect from subducting slab, but it is depressed to the depth of 720 km while there are obvious effects. The dispersion of converted points is still an unsolved problem which maybe result from the complex structure of the discontinuity, converted phases which were misjudged, or the assumption of one dimensional spherical earth model.
基金supported by the National Natural Science Foundation of China (Grant Nos. 42074101, 42374113, 42074103)the Central Public-interest Scientific Institution Basal Research Fund (Grant Nos. CEAIEF20220201, CEAIEF20230204)+1 种基金the Science & Technology Fundamental Resources Investigation Program (Grant No. 2023FY101500)the TianHe Qingsuo Special Fund Project。
文摘Upper mantle discontinuities play an important role in slab dynamics and mantle responses in the subduction zones.Despite increasing numbers of seismological observations in the Hindu Kush, fine structures of mantle discontinuities still remain less explored, highlighting less understood interactions of the Indian slab and discontinuities. Here we collected a large dataset of several dense seismic networks/arrays, extracted near-source SdP waves in P-wave codas using the N-th root slant stackings, and then systematically imaged upper mantle discontinuities around the Indian slab beneath Hindu Kush. In comparison with the IASP91 model, we confirmed an abrupt topographic transition of the 410-km discontinuity(410) from uplifts of up to 41 km to depressions of less than 20 km near the slab edge and a slightly depressed 660-km discontinuity(660) with depths of 660 to 668 km below the slab front, as well as a fluctuating 300-km discontinuity(300) with depths of 264 to 337 km. We suggest that the 410 is elevated by the Indian slab due to the interior coldness, and deepened near the slab edge by the hot upwelling slab-entrained mantle that escapes below the slab bottom. Based on a depressed 410 inside the Indian slab and a 660with slight depressions below the slab, we infer that the subducted Indian slab currently stretches into the upper MTZ. Moreover,we interpret the fluctuant 300 as the coesite to stishovite phase transition in the subduction-zone mantle enriched in the eclogite.When considered alongside other studies, our results can provide more insights into the dynamics of the Indian slab and mantle responses.
基金This work was supported by the Special Funds for the State Major Basic Research of China (Grant No. 95-13-04-06)the National Natural Science Foundation of China (Grant No. 49874020)the Ph.D. Programs Foundation of the Ministry of Education of Chi
文摘The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth root slant stack and digital records from networks in Germany and the western United States. Results show the obvious evidence for reflected and refractive phases associated with the 410 km and 660 km discontinuities. There may be discontinuities at other depths such as 150 km, 220 km and 520 km. The 410 km discontinuity is elevated and the 660 km discontinuity is depressed respectively, consistent with the expected thermal signature of the phase transitions. The subducting slab has penetrated into the lower mantle in the northern part of the Sea of Okhotsk, while it is stagnant on the 660 km discontinuity in the southern part.
基金the National Natural Science Foundation of China(Grant No.49874020) the Ph D Programs Foundation of Ministry of Education of China(Grant No.99000108).
文摘The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath Izu-Bonin and Japan Sea. The mantle discontinuities and the effects of subducting slab on the 660 km and 410 km discontinuities are studied. It is found that there are mantle discontinuities existing at the depths of 170, 220, 300, 410, 660, 850 and 1150 km. Beneath Izu-Bonin, the 410 km discontinuity is elevated, while the 660 km discontinuity is depressed; for both discontinuities, there are regionalized differences. Beneath Japan Sea, however, there is no depth variation of the 410 km discontinuity, and the 660 km discontinuity is depressed without obvious effect of the subducting slab.
