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191.
井间地震层析成像分辨率研究 总被引:12,自引:1,他引:11
通过大量数值模型试验,并根据射线密度、射线正交性和点扩散函数,对井间地震层析成像的分辨率问题进行了研究。结果表明,井间地震层析成像的分辨率在空间上是可能性变的,垂直方向的分辨率好于水平方向,而且高速异常体和低速异常体的图像形态和分辨率是非一致的。高速异常体波形CT的图像水平方向最小分辨率距离为1/2波长,垂直分辨率最小分辨率距离为3/10波长;而低速异常体的波形CT图像的水平方向的最小分辨率约为2/5波长,垂向最小分辨率约1/5个波长;走时CT的图像水平方向最小分辨率为3个像元,垂直方向的最小分辨率距离为2个像元;当井深与井间距之比为2时,图像分辨率最高。 相似文献
192.
工业CT技术在卫星产品检测中的应用 总被引:2,自引:0,他引:2
卫星产品许多都采用了焊接结构。为了保证其使用的安全可靠性,必须对焊缝进行l00%的无损检测。然而对于一些形状复杂的精密电子束焊件,由于产品尺寸小,加之焊缝周围结构的遮挡,使常规方法的应用受到了限制。工业CT技术具有不受试件材料种类、形状结构及表面状况限制的特点,能给出与试件材料密度及尺寸特性相对应的断层扫描图象,分辨率高,在检测复杂构件方面显示出了优势。本文介绍了卫星产品精密复杂焊接件对无损检测技术的具体要求,研究了卫星产品电子束焊缝的工业CT检测方法,包括设备、对比试样、检测工艺、评定方法等,并通过电磁阀、喷注器、自锁阀、减压器、加注/排放阀、单向阀、气滤、过滤器等具体产品检测实例,描述了工业CT技术在卫星产品检测中的应用。实际应用表明:工业CT是检测航天卫星产品精密复杂结构件焊缝缺陷的理想手段,其成象直观,缺陷的定位、定性和定量结果可靠,完全能满足产品的质量控制要求。目前,累计用工业CT检测卫星产品数批若干件,检测焊缝上千条。剔出有超标缺陷的产品40件,避免了隐患。经过工业CT检测的产品,己在"返回式卫星"、"风云二号"、"东方红三号"、"资源一号"、"中星-22号"等型号卫星中取得了成功应用。 相似文献
193.
Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by
unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged
joint) zones as a result of subterranean erosion by flowing groundwater. Because of the irregular distribution of pinnacles
and cutters on the bedrock surface, uncertainties arise when "hit-or-miss" borehole drilling is used to locate potential collapse
sites. A high-resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding
the drilling program. Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a site
in southern Indiana where limestone is covered by about 9 m of clayey soils. Forty-nine transects were conducted over an area
of approximately 42,037 m2. The electrode spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were interpreted with
the aid of soil borings. The repeatability of ERT was evaluated by comparing the rock surface elevations interpreted from
pairs of transects where they crossed each other. The average difference was 2.4 m, with a maximum of 10 m. The discrepancy
between interpreted bedrock-surface elevations for a transect intersection may be caused by variations in the subsurface geology
normal to the transect. Averaging the elevation data interpreted from different transects improved the ERT results. A bedrock
surface map was generated using only the averaged elevation data at the transect junctions. The accuracy of the map was further
evaluated using data from four exploratory boreholes. The average difference between interpreted and actual bedrock surface-elevations
was less than 0.4 m. The map shows two large troughs in the limestone surface: one coinciding with an existing sinkhole basin,
while the other is in alignment with a small topographic valley. Because sinkholes were observed at the same elevation interval
in similar valleys in the vicinity, the delineated trough may have implications for future land use at the site.
Received: 4 January 1999 · Accepted: 8 March 1999 相似文献
194.
Chang Li Robert D. van der Hilst M. Nafi Toksöz 《Physics of the Earth and Planetary Interiors》2006,154(2):180-195
We have produced a P-wave model of the upper mantle beneath Southeast (SE) Asia from reprocessed short period International Seismological Centre (ISC) P and pP data, short period P data of the Annual Bulletin of Chinese Earthquakes (ABCE), and long period PP-P data. We used 3D sensitivity kernels to combine the datasets, and mantle structure was parameterized with an irregular grid. In the best-sampled region our data resolve structure on scale lengths less than 150 km. The smearing of crustal anomalies to larger depths is reduced by a crustal correction using an a priori 3D model. Our tomographic inversions reveal high-velocity roots beneath the Archean Ordos Plateau, the Sichuan Basin, and other continental blocks in SE Asia. Beneath the Himalayan Block we detect high seismic velocities, which we associate with subduction of Indian lithospheric mantle. This structure is visible above the 410 km discontinuity and may not connect to the remnant of the Neo-Tethys oceanic slab in the lower mantle. Our images suggest that only the southwestern part of the Tibetan plateau is underlain by Indian lithosphere and, thus, that the upper mantle beneath northeastern Tibet is primarily of Asian origin. Our imaging also reveals a large-scale high-velocity structure in the transition zone beneath the Yangtze Craton, which could have been produced in multiple subduction episodes. The low P-wave velocities beneath the Hainan Island are most prominent in the upper mantle and transition zone; they may represent counter flow from the surrounding subduction zones, and may not be unrelated to processes beneath eastern Tibet. 相似文献
195.
几种静校正方法的比较研究 总被引:3,自引:4,他引:3
为解决近地表速度异常和地形起伏引起的静校正问题,已出现了多种静校正方法,这常常使资料处理人员无所适从。这里从众多的静校正方法中选择了三个具有代表性的,在生产中用得较多的方法(折射静校正、无射线追踪层析静校正、非线性层析静校正),从方法原理、方法特点、实际应用效果等方面进行了比较研究,最后给出了针对不同目标选择适当静校正方法的建议,以帮助资料处理人员在实际资料处理中,有针对性地选择静校正方法,快速有效地完成资料处理任务,提高处理质量。 相似文献
196.
最小生成树相位解缠中冗余去除算法 总被引:1,自引:0,他引:1
目前,相位解缠的方法中以Goldstein提出的枝切法最为经典,它通过枝切线将残差点相互连接使得残差点电荷中和,在相位展开处理的积分中,积分路径不能穿过分支,从而限制误差的传播。但是由于枝切线连接策略的不合理,往往造成连成的枝切线过多、过长,甚至多条枝切线形成闭合区域,造成不能解缠的“死区”,特别是在残差点较多的情况,这种现象更为严重。本文在最小生成树原理的基础上,提出的枝切线冗余去除算法能简单、准确地去除枝切树中的冗余,并保证了相位解缠具有最好的效果。 相似文献
197.
地震层析成像技术在岩体完整性测试中的应用 总被引:3,自引:0,他引:3
地震波层析成像借鉴了医学上X射线断面扫描的基本原理,利用地震波穿过地质体后走时及能量的改变等物理信息,通过数学处理重建地质体内部图像,从而得到所研究地质体的岩性及构造分布。本文利用这种方法,在一个钻孔中利用电火花震源激了弹性波,在另一个钻孔布设多个检波点同时接收,拾取弹性波初至时间,将接收到的数据利用SIRT方法进行反演迭代计算,最终形成一个弹性波速度谱图,然后利用岩土体的弹性波速度差异推断岩体完整性分布。与其它测试方法比较,该方法分辨率高,空间位置准确,在工程物探、岩土工程勘察中具有较好的应用前景。 相似文献
198.
Introduction The northwest of China includes Tarim, Junggar and Qaidam basins, and Kunlun, Tianshan, Altun and Qilian mountains, as well as the north part of the Tibetan Plateau. For a long time, the study of lithosphere structures and dynamics in this area has been a popular topic in geoscience, and has yielded many results. For example, TANG (1994) and LI et al (1998) suppose that the tectonic structure of Tarim Basin is various with geological periods, which changes many times betwee… 相似文献
199.
Jean -Luc Got Vadim Monteiller Jean Virieux Paul Okubo 《Pure and Applied Geophysics》2006,163(2-3):405-430
Seismic velocity parameters in limited, but heterogeneous volumes can be inferred using a double-difference tomographic algorithm,
but to obtain meaningful results accuracy must be maintained at every step of the computation. MONTEILLER et al. (2005) have devised a double-difference tomographic algorithm that takes full advantage of the accuracy of cross-spectral
time-delays of large correlated event sets. This algorithm performs an accurate computation of theoretical travel-time delays
in heterogeneous media and applies a suitable inversion scheme based on optimization theory. When applied to Kilauea Volcano,
in Hawaii, the double-difference tomography approach shows significant and coherent changes to the velocity model in the well-resolved
volumes beneath the Kilauea caldera and the upper east rift. In this paper, we first compare the results obtained using MONTEILLER
et al.'s algorithm with those obtained using the classic travel-time tomographic approach. Then, we evaluated the effect of using
data series of different accuracies, such as handpicked arrival-time differences (``picking differences'), on the results
produced by double-difference tomographic algorithms. We show that picking differences have a non-Gaussian probability density
function (pdf). Using a hyperbolic secant pdf instead of a Gaussian pdf allows improvement of the double-difference tomographic
result when using picking difference data. We completed our study by investigating the use of spatially discontinuous time-delay
data. 相似文献
200.