Upper-mantle shear velocity beneath eastern Australia from inversion of waveforms from SKIPPY portable arrays
Upper-mantle shear velocity beneath eastern Australia from inversion of waveforms from SKIPPY portable arrays
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DOI：
10.1111/j.1365-246x.1996.tb01530.x
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发表时间：
1996-10
影响因子：
2.8
通讯作者：
A. Zielhuis;R. Hilst
中科院分区：
文献类型：
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作者：
A. Zielhuis;R. Hilst
1993年，澳大利亚国立大学地球科学研究学院开始了一项全国性的地震测量项目SKIPPY，以便对澳大利亚大陆下面的上地幔进行全面研究。利用SKIPPY便携式阵列定位于澳大利亚东部时记录的宽带数据，采用波形反演技术，建立了澳大利亚东部及邻近海域上地幔和过渡带剪切速度的三维模型。SKIPPY数据由该地区永久地震观测站的数据增强。波形反演的第一步是将基模和高模瑞利波的波形与径向分层模型合成的波形进行匹配；在第二阶段，将剪切速度径向变化的线性约束结合到剪切速度非球面变化的层析反演中。首选模型将数据方差减少了90%。由于数据覆盖密集，横向尺寸大于250公里，纵向尺寸大于50公里的结构特征得以解决。从层析成像中推断出的主要结构特征是：(1)从大洋区到显生宙大陆和元古宙大陆区的高速“盖子”厚度大幅增加；(2)在澳大利亚东部地区下方140公里深处有一个明显的低速带，通常被称为塔斯曼褶皱带，这证实了先前从瑞利波频散曲线中得出的推断。(3)在大陆东部边缘下方有一个突出的低波速区，与新生代火山活动和热流增强区域重合；(4)在珊瑚海和塔斯曼海下方有深部低波速异常；(5)在澳大利亚东部地幔过渡带（深度410-660公里）有局部高波速扰动，特别是在新英格兰褶皱带和伊萨山地块下方。从图像中我们推断，前寒武纪盾的东部边界与强烈的地震对比并不一致，除非这个边界位于比通常假设的更东的地方。根据图像推断，澳大利亚东部的上地幔和过渡带的结构比澳大利亚中部和西部的前寒武纪克拉通的结构更为复杂，这可能是由于塔斯曼海打开之前东部大陆边缘的俯冲作用。如果这一解释是正确的，那么它就意味着部分上地幔在板块向北快速移动的过程中已经随着岩石圈横向移动了。
In 1993, the Research School of Earth Sciences of the Australian National University commenced a nationwide seismometry project, SKIPPY, for a comprehensive study of the upper mantle beneath the Australian continent. We applied a waveform inversion technique to broad-band data recorded while the SKIPPY portable arrays were positioned in eastern Australia in order to construct a 3-D model of shear velocity in the upper mantle and transition zone beneath eastern Australia and the adjacent oceanic regions. The SKIPPY data were augmented by data from the permanent seismological observatories in the region. The first step of the waveform inversion used involved the matching of the waveforms of fundamental- and higher-mode Rayleigh waves with waveforms synthesized from radially stratified models; in the second stage the linear constraints on radial variations in shear velocity were combined in a tomographic inversion for aspherical variations in shear velocity. The preferred model reduces the data variance by 90 per cent. Owing to the dense data coverage, structural features with dimensions larger than 250 km laterally and 50 km vertically are resolved. The major structural features inferred from the tomographic images are (1) a substantial increase in the thickness of the high-velocity ‘lid’ from the oceanic region to the Phanerozoic continental and Proterozoic continental regions, (2) a pronounced low-velocity zone centred at 140 km depth beneath the part of eastern Australia often referred to as the Tasman fold belt, which confirms previous inferences from Rayleigh-wave dispersion curves, (3) a prominent zone of low wave speeds beneath the eastern margin of the continent that coincides with locations of Cenozoic volcanism and regions of enhanced heat flow, (4) deep low-wave-speed anomalies beneath both the Coral and Tasman seas, and (5) localized high-wave-speed perturbations in the mantle transition zone (410-660 km depth) beneath eastern Australia, in particular beneath the New England fold belt and the Mount Isa block. From the images we infer that the eastern boundary of the Precambrian shields does not coincide with a sharp seismic contrast, unless this boundary is located further to the east than is commonly assumed. The structure of the upper mantle and transition zone beneath eastern Australia as inferred from the images is more complex than that beneath the Precambrian cratons of central and western Australia, which could be due to subduction beneath the eastern continental margin prior to opening of the Tasman sea. If correct, this interpretation would imply that part of the upper mantle has moved along laterally with the lithosphere during the relatively fast northward motion of the plane.