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Velocity structure and radial anisotropy beneath the northeastern tibetan plateau revealed by eikonal equation-based teleseismic P-wave traveltime tomography

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Science China Earth Sciences 2022年第5期65卷 824-844页

作者： Mengyang LI Shaolin LIU Dinghui YANG Xiwei XU Wenhao SHEN Chaodi XIE Wenshuai WANG Shuxin YANG National Institute of Natural Hazards Ministry of Emergency Management of ChinaBeijing 100085China School of Earth Sciences Yunnan UniversityKunming 650091China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China School of Mathematics and Statistics Ningxia UniversityYinchuan 750021China

The northeastern tibetan plateau serves as the frontier for the northeastward expansion of the *** this area,the tibetan plateau interacts with the surrounding blocks,such as the Alxa Block,the Ordos Block,the Kunlun-West Qinling belt and the Sichuan *** of this expansion and interaction,this area suffers from intense *** present,the evolution and deformation mechanisms of the northeastern tibetan plateau remain *** provide new insights into these mechanisms,in this study,we conduct tomography of the P-wave velocity and radial anisotropy structures beneath the northeastern tibetan *** choose a total of 667 teleseismic earthquakes from August 2006 to October *** of these earthquakes were recorded by 921 broadband seismic stations in the northeastern tibetan plateau and surrounding *** first perform cross-correlation on waveforms of each station pair and obtain 770,749 P-wave traveltime ***,we invert the differential traveltime data by applying eikonal equation-based teleseismic ***,the P-wave velocity and radial anisotropy structures at depths from 30 to 800 km below the northeastern tibetan plateau are *** tomographic model shows clear low-velocity anomalies and positive radial anisotropy in the lower crust under the northeastern Qilian orogen,the northeastern Songpan-Ganzi belt and the western Qinling fold *** features are integrated to demonstrate the existence of lower crustal flow in the study *** low-velocity anomalies and positive radial anisotropy are found in the uppermost mantle beneath the Qilian orogen,the northeastern Songpan-Ganzi belt and western Qinling fold *** characteristics are combined to infer a weak lithosphere and horizontal asthenospheric flow under these tectonic *** the Ordos Block and the Sichuan Basin exhibit clear high-velocity anomalies and negative radial anisotropy in the uppermost mantle,thereby reflect

关键词： northeastern tibetan plateau Tomography P-wave velocity Radial anisotropy structure Indian plate

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The impacts of base level and lithology on fluvial geomorphic evolution at the tectonically active Laohu and Hasi Mountains,northeastern tibetan plateau

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Science China Earth Sciences 2021年第6期64卷 906-919页

作者： Zhengchen LI Xianyan WANG Yang YU Huiping ZHANG Qi SU Xiaodong MIAO Huayu LU School of Geography and Ocean Science Nanjing UniversityNanjing210023China Institute of Geology China Earthquake AdministrationBeijing100029China School of Resource and Environmental Sciences Linyi UniversityLinyi276000China

Previous researches had emphasized tectonic impacts on the fluvial system at the tectonically active areas,while the effects of lithology and local base level change have received relatively rare *** we investigated fluvial landforms at different spatial scales,focusing on knickpoints and channel network reorganization from an area affected by the Haiyuan Fault in the northeastern tibetan *** geomorphic indices,i.e.,drainage pattern andχanomalies,were calculated and *** results show that two regional radial drainages formed around the Laohu and Hasi *** the interior of the radial drainage,tributaries from the southeast side of the Laohu Mountain experienced near 180°direction *** interpret this as the gradual drainage capture originating from the height difference(~190 m)of the local base level between the two *** tributaries from the Hasi Mountain show alternating gorges and broad valleys controlled by ***,tectonic uplift and the lowering of base level(from the incision of the Yellow River)triggered an autogenic positivefeedback transition from parallel to dendritic drainage *** observations suggest that base level change and lithology play a crucial role in landscape evolution,even in a tectonically active region.

关键词： River piracy Base level Lithology Geomorphic index Haiyuan Fault northeastern tibetan plateau

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Radial Anisotropy in the Crust beneath the northeastern tibetan plateau from Ambient Noise Tomography

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Journal of Earth Science 2015年第6期26卷 864-871页

作者： Jing Tan Hongyi Li Xinfu Li Ming Zhou Longbin Ouyang Sanjian Sun Dan Zheng Key Laboratory of Geo-Detection Ministry of Education China University of Geosciences Geological Exploration Technologies Institute of Anhui Province School of Geophysics and Information Technology China University of Geosciences

Through analysis of Rayleigh wave and Love wave Green＇s functions estimated from ambient noise tomography, we obtain radial anisotropy and shear wave velocity structure beneath the northeastern tibetan plateau. With two hundred and twenty three broadband seismic stations deployed by China Earthquake Administration, a collaborative seismic experiment of northern Tibet（ACSENT） experiment and northeastern Tibet seismic（NETS） experiment provide the unprecedented opportunity to resolve the spatial distribution of the radial anisotropy within the crust of the northeastern tibetan plateau. Discrepancies between Love（sh） and Rayleigh（sv） wave velocities show complex anisotropic patterns associated with the dynamic processes of the collision between the Indian and Eurasian plates：（1） In the upper crust, V（sv）〉V（sh） anisotropy is dominant throughout the study area which probably reflects fossil microcracks induced by the uplift, folding and erosion geodynamic processes;（2） in the middle crust, V（sh）〉V（sv） observed beneath the Songpan-Ganzi terrane and the northwestern Qilian orogen correlates well with a mid-crustal low velocity zone（LVZ）;（3） at depths deeper than 40 km, V（sh）〉V（sv） is still found in the Songpan-Ganzi terrane. This anisotropy could be caused by the sub-horizontal alignment of anisotropic minerals that has followed the collision between India and Eurasia. However, the northwestern Qilian orogen is associated with V（sv）〉V（sh） anisotropy which may be related to the vertically aligned seismic anisotropic minerals caused by the crustal thickening.

关键词： northeastern tibetan plateau ambient noise tomography radial anisotropy.

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Raindrop Size Distribution Measurements at High Altitudes in the northeastern tibetan plateau during Summer

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Advances in Atmospheric Sciences 2023年第7期40卷 1244-1256页

作者： Huibang HAN Yuxin ZHANG Jianbing TIAN Xiaoyan KANG Meteorological Disaster Prevention Technology Center in Qinghai Province Xining 810000China Key Laboratory for Disaster Prevention and Mitigation in Qinghai Province Xining 810000China

Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern tibetan *** analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 *** results show that the contribution of stratiform and convective precipitation with rain rate between 1≤Rnortheastern tibetan plateau.

关键词： raindrop size distribution precipitation microphysics northeastern tibetan plateau fall velocity

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Stable isotopes and chloride ion of precipitation events in the northeastern tibetan plateau, China

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Journal of Mountain Science 2021年第4期18卷 834-846页

作者： CUI Bu-li LI Dong-sheng JIANG Bao-fu WANG Ying WANG Ya-xuan WANG Long-sheng LI Xiao-yan State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing Normal UniversityBeijing 100875China School of Resources and Environmental Engineering Ludong UniversityYantai 264025China State Key Laboratory of Loess and Quaternary Geology Institute of Earth EnvironmentChinese Academy of SciencesXi’an 710061China

Stable isotopes and chloride ion of precipitation are ideal environmental tracers to explain and reveal the formation and evolution mechanisms of water bodies. It is crucial to investigate the stable isotopes and chloride in precipitation events in the northeastern part of the tibetan plateau(NETP) due to the limitation of available data. This study sampled each event of precipitation during the period from July 2018 to June 2019 and the monthly dustfall in the NETP to investigate the temporal changes of stable isotopes and chloride in precipitation, and to reveal the moisture source of precipitation over the NETP using a back trajectory model. Results showed that the δ^(2)H values of precipitation ranged from-183.51‰ to 17.75‰, and the δ^(18)O values ranged from-25.18‰ to 0.48‰. The slope of the Local Meteoric Water Line was slightly lower than 8 due to the effect of belowcloud secondary evaporation on the precipitation process. Most d-excess values were higher than 10‰ because moisture recycled from the continent and Qinghai Lake surface mixed with precipitation. The chloride in precipitation accounted for 86.5% of the annual total deposition mass of chloride(1329.64 mg/m2), indicating that precipitation was the main source of chloride in the NETP. The temperature and amount effects of stable isotope in the precipitation were obvious in the NETP. The precipitation was predominantly derived from the Westerly Circulation from September through May and the East Asian Monsoon from June to August, with precipitation amounts of 246.5 mm and 178.0 mm, respectively, indicating that the precipitation over the NETP brought by the Westerly Circulation was more than that brought by the East Asian Monsoon. The air mass over the NETP transited in late May and early September, and a slight change in transition period would mainly be related to the intensity of the East Asian Monsoon, which is strongly influenced by El Ni?o-Southern Oscillation. These results provide not only bas

关键词： Stable isotope Chloride ion Precipitation Moisture source northeastern tibetan plateau

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Geomorphometric Features of the Alluvial Fans around the Chaka-Qinghai Lake in the northeastern tibetan plateau

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Journal of Earth Science 2014年第1期25卷 109-116页

作者： Huiping Zhang Yuanyuan Lü State Key Laboratory of Earthquake Dynamics Institute of GeologyChina Earthquake Administration Key Laboratory of Saline Lake Resources and Environment Institute of Mineral ResourcesChinese Academy of Geological Sciences

This article aims to study the geomorpometric features of alluvial fans since they act as a small-scale geomorphic unit response to tectonics and climate changes around the Chaka-Qinghai Lake area in the northeastern tibetan plateau. We quantitatively extracted geomorphic parameters, such as the surface area and slope of alluvial fans adjacent to the Qinghai Nan Shan and Ela Shan. Alluvial fans in the Chaka Lake partition area, south of the Qinghai Nan Shan, are featured by a small area and short length, but the largest slope. Geomorphic parameters of the alluvial fans in Ela Shan area are in- termediate in size, and the alluvial fans in the Qinghai Lake partition area north of Qinghai Nan Shan have the gentlest slope. Together with the regional faulting activity analysis, we suggest that the alluvial fans with the high slopes in the south of Qinghai Nan Shan are mainly controlled by the reverse faulting along the Qinghai Nan Shan faults, and the strike-slip movement of the Eia Shan fault zone plays a weak role. In contrast, due to the lack of active faults, the alluvial fans near the Qinghai Lake area north of the Qinghai Nan Shan only respond to regional erosion, transportation, and deposition proc- esses, thereby forming relatively gentle geomorphic units.

关键词： northeastern tibetan plateau Chaka-Qinghai Lake alluvial fan geomorphometric fea- ture geomorphic process.

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Typical Geochemical Elements in Loess Deposit in the northeastern tibetan plateau and Its Paleoclimatic Implication

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Acta Geologica Sinica(English Edition) 2006年第1期80卷 110-116页

作者： TAN Hongbing MA Haizhou ZHANG Xiying LU Huayu WANG Jianguo Institute of Salt Lakes Chinese Academy of Sciences Xining Qinghai 810008 Institute of Earth Environment Chinese Academy of Sciences Xi＇an Shaanxi 710075

Widespread and thick loess deposit in the northeastern tibetan plateau records paleoclimatic changes over the Quaternary period. In this study, we investigate a loess section located in a high terrace of the Huangshui River in the Xining Basin, and collect samples at 20-cm intervals by digging a well of 16-m depth （including paleosol S1 and SO and several loess interlayers over the last glacial-interglacial cycle and the Holocene）. Concentration of some active elements （Sr and Ca） and inert elements （Rb, Zr, Ti） in these loess samples are measured. The results show that ratios of those elements （oxide）, such as Rb/Sr, Ti/Sr, and Zr/CaO ratios, would indicate sensitively paleoclimatic changes, especially the history of precipitation over the last glacial-interglacial and the Holocene. Moreover, the curves of Rb/Sr, Ti/Sr, and Zr/CaO ratios had almost the same variable trends from the bottom to the top and also closely correlated with values of magnetic susceptibility and the global marine δ^18O record. But compared with the curves of magnetic susceptibility, the changes of ratios of these elements （oxide） are clearer and easy to understand. Therefore, the ratios of these typical chemical elements in the loess deposit may be used as an excellent index to investigate the history of paleoclimate, particularly precipitation changes in the northeastern tibetan plateau.

关键词： northeastern tibetan plateau loess aleosol geochemical elements paleoclimate

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Attenuation relations for horizontal peak ground acceleration and response spectrum in northeastern tibetan plateau region

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Acta Seismologica Sinica(English Edition) 2004年第6期17卷 651-661页

作者： YU Yan-xiang(俞言祥) WANG Su-yun(汪素云) Institute of Geophysics China Earthquake Administration Beijing 100081 China Institute of Geophysics China Earthquake Administration Beijing 100081 China

The seismic intensity attenuation relations in northeastern tibetan plateau region are established by a regression analysis on isoseismal data. Then the attenuation relations for horizontal peak ground acceleration and short-period response spectrum for western North America are derived based on the database of HUO Jun-rong and strong mo-tion data from recent earthquakes. The attenuation relations of long-period response spectrum for western North America are developed by analyzing the broadband digital seismic recordings of southern California. By integrat-ing the short-period and long-period attenuation relationships, the attenuation relations for horizontal acceleration response spectrum in the period range of 0.04~6 s for western North America are established. The attenuation equation that accounts for the magnitude saturation and near-field saturation of high frequency ground motion is used. Finally the attenuation relations for horizontal peak ground acceleration and response spectrum for the region of northeastern tibetan plateau are developed by using the transforming method.

关键词： attenuation relation response spectrum northeastern tibetan plateau

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Crustal structure of northeastern tibetan plateau and Ordos block:Waveform interpretation of the Maqen-Jingbian seismic refraction profile

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Earthquake Science 2009年第4期22卷 365-371页

作者： Fuyun Wang Hong Shang Xiankang Zhang Geophysical Exploration Center China Earthquake Administration Zhengzhou 450002 China

The Maqen-Jingbian wide-angle seismic reflection and refraction experiment was carried out in 1998, which aims at determining detailed structure in the crust and top of the upper mantle and understanding structural relation between the northeastern tibetan plateau and the Ordos block. The 1-D crustal models inferred by waveform inversion show strong variations in crustal structure, which can be classified into four different types： ① an Ordos platform with the Proterozoic crust and two high-velocity layers in the northeast section, ② a transitional crust between the northeastern tibetan plateau and the Ordos block across the Haiyuan earthquake zone, ③ the Qilian orogenic zone in the central part, and ④ the Qinling orogenic zone in the southwestern section. The Moho depth increases from -42 km to -62 km from the NE part to the SW part of the profile. The crystalline crust consists of the upper crust and lower crust in northeastern tibetan plateau. There is an obviously low P-wave velocity layer dipping northeastward, which is 12-13 km thick, at the bottom of the upper crust in Qinling orogenic zone and Haiyuan earthquake zone. The lower crust is characterized by alternating high and low P-wave velocity layers. Beneath Ordos block, i.e., the NE part of the profile, the crust shows quite a smooth increase in P-wave ve- locity down to the Moho at a depth of about 42 km.

关键词： crustal structure northeastern tibetan plateau Ordos block waveform interpretation seismic refraction

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200-kg large explosive detonation facing 50-km thick crust beneath west Qinling,northeastern tibetan plateau

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Earthquake Science 2009年第4期22卷 389-393页

作者： Qiusheng Li Rui Gao Haiyan Wang Jisheng Zhang Zhanwu Lu Pengwu Li Ye Guan Rizheng He Lithosphere Research Centre Institute of Geolog) Chinese Academy of Geological Sciences Beijing 100037 China Eearthprobe and Geodynamics Open Laboratory of Chinese Academy of Geological Sciences Beijing 100037 China

It is difficult to acquire deep seismic reflection profiles on land using the standard oil-industry acquisition parameters. This is especially true over much of tibetan plateau not only because of severe topography and rapid variation of both velocity and thickness of near-surface layer, but also strong attenuation of seismic wave through the thickest crust of the Earth. Large explosive sources had been successfully detonated in US, but its application in tibetan plateau rarely has an example of good quality. Presented herein is the data of a 200-kg single shot we recorded in west Qinling, northeastern tibetan plateau. The shot gather data with phenomenal signal-to-noise ratios illustrate the energy of the Prop phase. Although the observations are only limited to the northeastern tibetan plateau and thus cannot comprise an exhaustive study, they nevertheless suggest that large explosions may be a useful exploration tool in tibetan plateau where standard seismic sources and profiling methods fail to produce adequate data of low crust.

关键词： northeastern tibetan plateau deep seismic reflection profile Moho, large explosive sources

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