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91.
Chongjin Zhao Luolei Zhang Peng Yu Yuzhu Liu Shaokong Feng 《Geophysical Prospecting》2019,67(7):1764-1777
In this work, we propose a method for determining reflection travel times based on the acquisition of first-arrival travel times via the fast sweeping method. The accuracy of this scheme was proven by conducting model experiments to establish a foundation for first-arrival tomography, reflection tomography and combined tomography. Reflection tomography was subsequently achieved using the adjoint-state method; on this basis, we propose a combined tomography method involving both first-arrival and reflection tomography. In the model experiments, excellent results were obtained via first-arrival tomography, reflection tomography and our combined tomography method. Finally, full-waveform inversion was performed, with the inversion produced by combined tomography used as the initial model. Excellent results were obtained using this approach. However, combined tomography reproduced and characterized the model much more realistically. 相似文献
92.
本文选取河南及邻区39个宽频带和甚宽频带地震台站记录的2014年1月~2015年12月垂直分量的连续波形资料,通过波形互相关和叠加运算得到台站间的经验格林函数,并用时频分析方法提取了498条瑞利波群速度频散曲线,进而采用噪声层析成像方法反演获得了河南及邻区8~25s的瑞利波群速度分布图像。结果表明,8s周期的群速度分布与地表构造特征密切相关,平原地区表现为低速异常,而基岩出露的山区呈现为高速异常;14s、20s周期的群速度在山区表现的高速异常与8s相似,说明中上地壳与地壳浅部结构有一定的相关性和继承性;8~20s周期的群速度在华北平原地区存在低速异常范围随周期增加而减小的现象。华北平原地区在下地壳表现出的低速异常,可能与大陆地壳减薄有关。大致以太行-武陵重力梯度带为界,下地壳表现出的西部低速、东部至研究区中部高速异常差异,体现了地壳东薄西厚的结构特征。 相似文献
93.
Colliding Blast Waves Driven by the Interaction of a Short-Pulse Laser with a Gas of Atomic Clusters
Roland A. Smith James Lazarus Matthias Hohenberger Alastair S. Moore Joseph S. Robinson Edward T. Gumbrell Mike Dunne 《Astrophysics and Space Science》2007,307(1-3):131-137
Collisions between shocks are commonly found in many astrophysical objects, however robust numerical models or laboratory
analogues of these complex systems remain challenging to implement. We report on the development of scaled laboratory experiments
which employ new techniques for launching and diagnosing colliding shocks and high Mach number blast waves, scalable to a
limited subset of astrophysically-relevant regimes. Use of an extended medium of atomic clusters enables efficient (>80%)
coupling of 700 fs, 1 J, 1054 nm laser pulses to a “cluster” gas with an average density of ≈1019 particles cm−3, producing an initial energy density >105 J cm−3, equivalent to ≈5×109 J/g. Multiple laser foci are used to tailor the spatial profile of energy deposition, or to launch pairs of counter-propagating
cylindrical shocks which then collide. By probing the collision interferometrically at multiple view angles in 5^ increments and applying an inverse Radon transform to the resulting phase projections we have been able to tomographicall
reconstruct the full three-dimensional, time-framed electron density profile of the system. 相似文献
94.
95.
Shear zones in porous sand: Insights from ring-shear experiments and naturally deformed sandstones 总被引:2,自引:1,他引:2
In a high-resolution small-scale seismic experiment we investigated the shallow structure of the Wadi Araba fault (WAF), the principal fault strand of the Dead Sea Transform System between the Gulf of Aqaba/Eilat and the Dead Sea. The experiment consisted of 8 sub-parallel 1 km long seismic lines crossing the WAF. The recording station spacing was 5 m and the source point distance was 20 m. The first break tomography yields insight into the fault structure down to a depth of about 200 m. The velocity structure varies from one section to the other which were 1 to 2 km apart, but destinct velocity variations along the fault are visible between several profiles. The reflection seismic images show positive flower structures and indications for different sedimentary layers at the two sides of the main fault. Often the superficial sedimentary layers are bent upward close to the WAF. Our results indicate that this section of the fault (at shallow depths) is characterized by a transpressional regime. We detected a 100 to 300 m wide heterogeneous zone of deformed and displaced material which, however, is not characterized by low seismic velocities at a larger scale. At greater depth the geophysical images indicate a blocked cross-fault structure. The structure revealed, fault cores not wider than 10 m, are consistent with scaling from wear mechanics and with the low loading to healing ratio anticipated for the fault. 相似文献
96.
97.
98.
CT对隐性骨折的诊断价值 总被引:1,自引:0,他引:1
目的:探讨CT对隐性骨折的诊断价值。方法:回顾性分析84例隐性骨折患者,其中男64例,女20例,年龄7 ̄73岁,平均42.6岁。所有患者均行轴位或冠状位CT扫描。结果:扫描发现脊柱骨折28例,髋臼骨折8例,胫骨平台骨折11例,眶骨骨折12例,颞骨骨折13例。肩胛骨骨折12例。结论:CT对隐性骨折的诊断具有极大价值,对于高度怀疑骨折而X线片未显示骨折征象的患者应进一步给予CT扫描检查。 相似文献
99.
100.
青藏高原东南缘岩石圈变形强烈、地震活动频繁,对其深部结构进行研究有助于提高对其演化及强震发震机理等问题的认识.本研究利用青藏东南缘固定和流动观测台站记录的地震P波走时数据,采用体波走时层析成像方法得到研究区地壳、上地幔顶部三维P波速度结构.结果显示,峨眉山大火成岩省内带范围呈明显的高速异常,推测为二叠纪时期地幔柱活动残留在地壳内的基性和超基性幔源物质.川西北次级块体和大火成岩省内带东西两侧存在低速带,可能是壳内部分熔融存在和中下地壳流动的证据:高原物质向南运移时受大火成岩省壳内高速体阻挡后分为两支,东支沿安宁河断裂—则木河断裂—小江断裂延伸,西支沿红河断裂向上地壳运移并逐渐穿过红河断裂.云南漾濞MS6.4地震序列全部位于西支低速通道之上,推测构造块体SE向运动和地壳流作用使得应力在上地壳震源区进一步集中,共同驱动断裂活动导致漾濞地震发生. 相似文献