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261.
262.
青藏高原现代降水中dδ^18O/dT的变化 总被引:3,自引:2,他引:3
不同时间尺度dδ^18O/dT的天气气候意义是不同的,其数值大小也是不一样的。本根据对青藏高原沱沱河、德令哈、西宁三站大气降水中δ^18O与温度关系的分析,并与具有长序列资料的地区进行比较。初步给出了青藏高原不同时间尺度dδ^18O/dT之间的差异。 相似文献
263.
The phase velocities of Rayleigh waves and the lateral variation of lithospheric structure in Tibetan Plateau 总被引:1,自引:0,他引:1
According to a Sino-U. S. joint project, eleven broadband digital PASSCAL seismometers had been deployed inside the Tibetan
Plateau, of which 7 stations were on the profile from Lhasa to Golmud and other 4 stations situated at Maxin, Yushu, Xigatze
and Linzhi. Dispersions and phase velocities of the Rayleigh surface waves (10s–120s) were obtained on five paths distributed
in the different blocks of Tibetan Plateau. Inversions of the S-wave velocity structures in Songpan-Ganzi block, Qiang-Tang
block, Lhasa block and the faulted rift zone were obtained from the dispersion data. The results show that significant lateral
variation of the S-wave velocity structures among the different blocks exists. The path from Wenquan to Xigatze (abbreviated
as Wndo-Xiga) passes through the rift-zone of Yadong-Anduo. The phase velocities of Rayleigh waves from 10s to 100s on this
path are significantly higher than that on other paths. The calculated mean crustal velocity on this path is 3.8 km/s, much
greater than that on other paths, where mean crustal velocities of 3.4–3.5 km/s are usually observed. Low velocity zones with
different thicknesses and velocities are observed in the middle-lower crust for different paths. Songpan-Ganzi block, located
in the northern part of Tibetan Plateau is characterized by a thinner crust of 65 km thick and a prominent low velocity zone
in the upper mantle. The low velocity zone with a velocity of 4.2 km/s is located at a depth form 115 km to 175 km. While
in other blocks, no low velocity zone in the upper mantle is observed. The value of Sn in Songpan-Ganzi is calculated to be
4.5 km/s, while those in Qiang-Tang and Lhasa blocks are about 4.6 km/s.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 566–573, 1992. 相似文献
264.
Preliminary study of crust-upper mantle structure of the Tibetan Plateau by using broadband teleseismic body waveforms 总被引:2,自引:0,他引:2
Lu-Pei Zhu Rong-Sheng Zeng Francis T. Wu Thomas J. Owens George E. Randall 《地震学报(英文版)》1993,6(2):305-316
As part of a joint Sino-U.S. research project to study the deep structure of the Tibetan Plateau, 11 broadband digital seismic
recorders were deployed on the Plateau for one year of passive seismic recording. In this report we use teleseimic P waveforms
to study the seismic velocity structure of crust and upper mantle under three stations by receiver function inversion. The
receiver function is obtained by first rotating two horizontal components of seismic records into radial and tangential components
and then deconvolving the vertical component from them. The receiver function depends only on the structure near the station
because the source and path effects have been removed by the deconvolution. To suppress noise, receiver functions calculated
from events clustered in a small range of back-azimuths and epicentral distances are stacked. Using a matrix formalism describing
the propagation of elastic waves in laterally homogeneous stratified medium, a synthetic receiver function and differential
receiver functions for the parameters in each layer can be calculated to establish a linearized inversion for one-dimensional
velocity structure.
Preliminary results of three stations, Wen-quan, Golmud and Xigatze (Coded as WNDO, TUNL and XIGA), located in central, northern
and southern Plateau are given in this paper. The receiver functions of all three stations show clear P-S converted phases.
The time delays of these converted phases relative to direct P arrivals are: WNDO 7.9s (for NE direction) and 8.3s (for SE
direction), TUNL 8.2s, XIGA 9.0s. Such long time delays indicate the great thickness of crust under the Plateau. The differences
between receiver function of these three station shows the tectonic difference between southern and north-central Plateau.
The waveforms of the receiver functions for WNDO and TUNL are very simple, while the receiver function of XIGA has an additional
midcrustal converted phase. The S wave velocity structures at these three stations are estimated from inversions of the receiver
function. The crustal shear wave velocities at WNDO and TUNL are vertically homogeneous, with value between 3.5–3.6 km/s down
to Moho. This value in the lower crust is lower than the normal value for the lower crust of continents, which is consistent
with the observed strong Sn attenuation in this region. The velocity structure at XIGA shows a velocity discontinuity at depth
of 20 km and high velocity value of 4.0 km/s in the midcrust between 20–30 km depth. Similar results are obtained from a DSS
profile in southern Tibet. The velocity under XIGA decreases below a depth of 30 km, reaching the lowest value of 3.2 km/s
between 50–55 km. depth. This may imply that the Indian crust underthrusts the low part of Tibetan crust in the southern Plateau,
forming a “double crust”. The crustal thickness at each of these sites is: WNDO, 68 km; TUNL, 70 km; XI-GA, 80 km.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 581–592, 1992. 相似文献
265.
Moment tensors of eleven major earthquakes in the Tibetan Plateau and its surrounding region from 1966 to 1980 are estimated
by generalized inverse technique. The seismic source time function and focal depth are immediately determined in the inversion.
The results show that moment tensors of some events differ significantly from double couple, the deviation increases with
decreasing plunge angle of null axis. All these events occurred in the upper crust, much shallower than those reported so
far, for example, in NEIS Bulletin. Focal mechanism solution obtained from the moment tensors are consistent with the idea
that the Indian plate collides northwards with the Eurasian plate and that an eastward spreading exists in the crust of the
Tibetan Plateau. The stress drops for earthquakes of intraplate are systematically higher than those of earthquakes in suture
zone. The source process duration becomes longer with seismic moment, but for the same seismic moment, the process duration
for earthquakes in suture zone is about 1.4 times of those for intraplate event, these results suggest that the earthquakes
near suture zone may be of a special characteristics in source process differently from those in intraplate.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 423 – 434, 1992. 相似文献
266.
青藏高原地理环境研究进展 总被引:27,自引:4,他引:23
经三纪青藏地区曾二次隆升与夷平,3,4Ma以来经历了高原强烈隆起,现代季风形成,高原山地抬升、进入冰冻圈,环境剧烈波劝,高原内部干旱化及全新世环境波动变化等古寺理演化阶段。 相似文献
267.
268.
青藏高原物质东流的岩石层力学背景探讨 总被引:3,自引:0,他引:3
利用地表大地热流观测资料、岩石生热率及热导率数据研究了三江和四川盆地 6个地区的岩石层平均温度结构及强度分布。结果表明 ,整个三江地区岩石层温度较高 ,而四川盆地温度较低 ;在岩石层强度分布上 ,四川盆地为高强度区 ,而三江地区则为低强度区 ;整个三江地区构成了一条青藏高原物质东流的低强度通道 ;由于四川盆地高强度块体的阻挡 ,青藏高原向东的物质流在此转向近南向 ,沿三江地区流逸 ;不同岩石层块体的强度差异可能是控制高原物质流动态势的重要力学背景之一。 相似文献
269.
高原季风强弱对南亚高压活动的影响 总被引:17,自引:10,他引:7
分析了高原季风强弱对夏季南亚高压活动和三峡库区旱涝的影响,揭示了如高原夏季风偏强(弱),育藏高原上空及其以东地区100hPa南亚高压也偏强(弱),位置偏北偏东(偏南偏西)。高原季风强年,南亚高压脊线6月北跳比多年平均早1候,8月南撤晚1~2侯;高原季风弱年。脊线北跳晚1~2候,南撤早1候。同时显示了高原夏季风强年,5~6月三峡库区降水随着南亚高压脊线北移而增多,7~8月三峡库区降水减少;高原夏季风弱年,主汛期前期库区降水少,后期降水略有增多。 相似文献
270.
温室效应对青藏高原及青藏铁路沿线气候影响的数值模拟 总被引:25,自引:12,他引:13
在一个全球模式中嵌套了RegCM2区域气候模式,进行了CO2加倍对中国区域气候影响的数值试验,对青藏高原及青藏铁路沿线地区进行了重点分析。结果表明,在CO2加倍的情况下,这里的气温将明显升高,升高值一般在2.6~2.8℃以上,高于全国平均值。同时降水在青藏高原大部分地区也将明显增加;其中青藏铁路沿线的增加率一般在25%以上,远高于全国平均值水平。温室效应同时会使得青藏铁路沿线的日平均最高气温升高。 相似文献