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171.
利用地震层析成象技术确定横向非均匀介质中的速度分布和界面位置 总被引:2,自引:0,他引:2
本文提出一种横向非均匀介质中的地震层析成象方法,由地震走时资料确定介质的速度分布和界面位置。计算中采用了参数分离、变阻尼、奇异值分解等技术,方程的解较稳定,且可得到解的分办。除反射波外,该方法还可同时利用分析波的资料。因此,适宜于折射及宽角度反射地震测深剖面的资料处理。数字试验结果表明,在模型内部,该方法能得到可靠的反演结果。在边界附近效果较差,受初始值影响较大。 相似文献
172.
腰椎管侧隐窝分型及影响侧隐窝狭窄症诊断的几个因素(附120例CTM分析) 总被引:1,自引:0,他引:1
作者对120例因下腰痛手术治疗在术前进行过CTM检查的患者作了影像学及临床分析.按形态不同,侧隐窝可分为五种类型:(1)三角型,即整个椎管呈倒三角形,其侧隐窝完全开放;(2)猫耳型,因后关节和椎体后缘轻度增生,形成底宽顶尖的侧隐窝,整个椎管形如猫头,侧脸窝为猫耳,基本开放;(3)牛角型,因关节突向椎体方向过度增生使侧隐窝呈横向伸开的带状,中央椎管不窄,横断面形如牛头,侧阴窝为牛角,严重者侧隐窝可近于闭塞;(4)三叶草型,极度增生的关节突加上向后实入的椎体后缘使整个椎管呈三叶草状,侧隐窝和中央椎管均狭窄;(5)混合型,多为上述形状的混合或两侧侧隐窝发育不对称.前二型不易形成对神经的压迫,后三型易造成压迫.但即使最狭窄的侧隐窝也不一定产生症状,因为关键在于神经根和侧隐窝的宽度的相对关系.因此作者提出单纯依靠侧隐窝的宽度不能诊断侧隐窝狭窄症,而是要判断神经是否被侧隐窝压迫.因此CTM在侧隐窝狭窄症的诊断中有突出意义. 相似文献
173.
Deep-large faults in the central continental margin of eastern China are well developed. Based on the regularity of spatial
and temporal distribution of the faults, four fault systems were divided: the Yanshan orogenic belt fault system, the Qinling-Dabie-Sulu
orogenic belt fault system, the Tanlu fault system and the East China Sea shelf basin-Okinawa trough fault system. The four
fault systems exhibit different migration behaviors. The Yanshan orogenic belt fault system deflected from an EW to a NE direction,
then to a NNE direction during the Indo-Chinese epoch-Yanshanian epoch. The thrust-nappe strength of the Qinling-Dabie orogenic
belt fault system showed the tendency that the strength was greater in the south and east, but weaker in the north and west.
This fault system faulted in the east and folded in the west from the Indo-Chinese epoch to the early Yanshanian epoch. At
the same time, the faults also had a diachronous migration from east to west from the Indo-Chinese epoch to the early Yanshanian
epoch. On the contrary, the thrust-nappe strength was greater in the north and west, weaker in the south and east during the
late Yanshanian epoch-early Himalayan epoch. The Tanlu fault system caused the basin to migrate from west to east and south
to north. The migration regularity of the East China Sea shelf basin-Okinawa trough fault system shows that the formation
age became younger in the west. The four fault systems and their migration regularities were respectively the results of four
different geodynamic backgrounds. The Yanshan orogenic belt fault system derived from the intracontinental orogeny. The Qinling-Dabie-Sulu
orogenic belt fault system derived from the collision of plates and intracontinental subduction. The Tanlu fault system derived
from the strike-slip movement and the East China Sea shelf basin-Okinawa trough fault system derived from plate subduction
and retreat of the subduction belt.
Translated from Journal of Jilin University (Earth Science Edition), 2005, 35(5): 554–563 [译自: 吉林大学学报 (地球科学版)] 相似文献
174.
三江盆地前进坳陷XDLZ地区构造较复杂,以往开展的二维叠后时间偏移成像精度低和空间位置不够准确,为此进行了二维叠前时间偏移处理研究,分析了Kirchhoff积分法叠前时间偏移处理中关键环节技术参数(叠前去噪、振幅补偿、反褶积、静校正、均方根速度建模和偏移孔径选取)对研究区复杂构造成像的影响及处理技巧。通过叠前时间偏移和叠后时间偏移在该区的应用效果对比分析,Kirchhoff积分法叠前时间偏移处理结果包含地震信息更加丰富,深层复杂构造成像在同相轴的连续性和断层及断点空间位置更趋合理,成像相位和振幅误差较小,构造成图精度提高了约4%。 相似文献
175.
To tackle the difficulties of a 3-D full volume prestack migration based on the double-square-root (DSR) one-way wave equation
in practical applications, the common-azimuth migration approach is first discussed using dual-domain wave propagators under
the theoretical frame of crossline common-offset migration. Through coordinate transforming, a common-azimuth prestack tau
migration technology that recursively continues the source and receiver wavefields and picks up the migrated results in the
two-way vertical traveltime (tau) direction is developed. The migrations of synthetic data sets of SEG/EAGE salt model prove
that our common-azimuth migration approaches are effective in both depth and tau domains. Two real data examples show the
advantages of wave-theory based prestack migration methods in accuracy and imaging resolution over the conventional Kirchhoff
integral methods.
Translated from Oil Geophysical Prospecting, 2006, 41(6): 629–634 [译自: 石油地球物理勘探] 相似文献
176.
Michael C. Ewers 《GeoJournal》2007,68(2-3):119-130
Urban areas compete with one another for people, goods, capital, ideas and other inputs of economic activity. Under the rubric
of globalization, instead of only maintaining or improving the initial stock of assets in a city, the power of a place to
attract outside flows of economic activity from elsewhere is increasingly important to economic development. Similarly, global
or world cities are characterized as the command and control points through which these global economic flows operate. In
response to the heightened mobility of highly-skilled labor across national borders, research has begun to examine the role
of international human capital as an economic flow. This paper will examine the role of places in determining where the highly-skilled
go in the global economy by viewing global city command and control functions as requiring unique labor flows. By reviewing
the evidence found in the literature, we can better understand the potential for urban areas to compete for highly-skilled
labor in the global economy. Known indicators of place attractiveness are assessed to examine the relationship between the
economic trajectories of cities and their labor requirements. Cities are situated between firms and states as the key place-based
actors which influence the mobility of highly-skilled labor. Finally, the paper also examines measurement issues and methodological
problems in creating indices of world cities as well as explores possibilities for new research. 相似文献
177.
Tadashi Kito reas Rietbrock Christine Thomas 《Geophysical Journal International》2007,169(3):1201-1209
We have developed a new array method combining conventional migration with a slowness-backazimuth deviation weighting scheme. All seismic traces are shifted based on the theoretical traveltime of the scattered wave from specific gridpoints in a 3-D volume. Observed slowness and backazimuth are calculated for each raypath and compared with theoretical values in order to estimate slowness and backazimuth deviations. Subsequently, stacked energy calculated by a conventional migration method is weighted by the slowness and backazimuth deviations to suppress any arrival energy whose slowness and backazimuth are inconsistent with the expected theoretical values. This new method was applied to two P- wave data sets which comprise (1) underside reflections at the 410 and 660 km mantle discontinuities and (2) D" reflections as well as their corresponding synthetic data sets. The results show that the weighting scheme dramatically increases the resolution of the migrated images and enables us to obtain well-constrained, focused images, making upper-mantle discontinuities and D" reflections more distinct by reducing their surrounding energy. 相似文献
178.
179.
Pb and Th in settling particles in the western Northwest Pacific Ocean: Particle flux and scavenging
A mooring of three conical time-series sediment traps was deployed at two sites in the western Northwest Pacific Ocean for 9 months. Total mass fluxes and activities of 210Pb and 230Th were determined for the settling particles to elucidate their scavenging and transport processes. Sediment samples also were analyzed for 210Pb activities. Total mass fluxes, 210Pb fluxes and 230Th fluxes showed large seasonal variations and their weighted mean fluxes tended to increase with depth, with an especially large increase near-bottom. The ratios of the observed 210Pb fluxes to the 210Pb deficiency fluxes in the upper traps at the two sites were only 0.02 and 0.12, and were attributable to advective export of 210Pb from the surface waters. Those ratios in the near-bottom traps ranged between 1.22 and 2.63. This suggests that these high ratios are due to effective particle scavenging, large lateral 210Pb import and input of resuspended particles that have not become incorporated into the sediments. The mean total 230Th fluxes at the near-bottom traps were 4.2–6.7 times higher than that expected from production in the overlying water column. The 210Pb activities in the surficial sediments were much lower than those in the near-bottom traps. The 210Pb accumulation rates estimated from the excess 210Pb inventory in the sediment column were 40–70% higher than the mean 210Pb fluxes at the near-bottom traps. The ratios of the 210Pb accumulation rates to the 210Pb deficiency fluxes at the near-bottom traps ranged between 2.0 and 3.7. The high fluxes of particulate 210Pb and 230Th at the near-bottom traps reflected a combination of enhanced scavenging of dissolved nuclides and the lateral redistribution of particulate matter by downslope and alongshore transports. However, it was not possible to discriminate among the various processes contributing to high nuclide fluxes. 相似文献
180.
An eruption on the eastern flank of Piton de la Fournaise volcano started on 16 November, 2002 after 10 months of quiescence.
After a relatively constant level of activity during the first 13 days of the eruption, lava discharge, volcanic tremor and
seismicity increased from 29 November to 3 December. Lava effusion suddenly ceased on 3 December while shallow earthquakes
beneath the Dolomieu summit crater were still recorded at a rate of about one per minute. This unusual activity continued
and increased in intensity over the next three weeks, ending with the formation of a pit crater within Dolomieu. Based on
ground deformation, measured by rapid-static and continuous GPS and an extensometer, seismic data, and lava effusion patterns,
the eruptive period is divided into five stages: 1) slow summit inflation and sporadic seismicity; 2) rapid summit inflation
and a short seismic crisis; 3) rapid flank inflation, onset of summit deflation, sporadic seismicity, accompanied by stable
effusion; 4) flank inflation, coupled with summit deflation, intense seismicity, and increased lava effusion; and finally
5) little deflation, intense shallow seismicity, and the end of lava effusion. We propose a model in which the pre-intrusive
inflation of Stage 1 in the months preceding the eruption was caused by a magma body located near sea level. The magma reservoir
was the source of an intrusion rising under the summit during Stage 2. In Stage 3, the magma ponded at a shallow level in
the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano,
causing lava effusion. Pressure decrease in the magmatic plumbing system followed, resulting in upward migration of a collapse
front, forming a subterranean column of debris by faulting and stoping. This caused intense shallow seismicity, increase in
discharge of lava and volcanic tremor at the lateral vent in Stage 4 and, eventually the formation of a pit crater in Stage
5. 相似文献