A data‐adaptive, multiscale approach of finite‐frequency, traveltime tomography with special reference to P and S wave data from central Tibet
A data‐adaptive, multiscale approach of finite‐frequency, traveltime tomography with special reference to P and S wave data from central Tibet
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DOI：
10.1029/2010jb008190
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发表时间：
2011-06
影响因子：
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通讯作者：
S. Hung;Wang-Ping Chen;L. Chiao
中科院分区：
文献类型：
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作者：
S. Hung;Wang-Ping Chen;L. Chiao
[1]我们讨论了一种创新的走时层析成像，结合小波，多尺度参数化和有限频率理论，以解决两个突出的问题，不可避免地产生不均匀的源站分布和三维（3-D）波前愈合的性质：如何客观地解决固有的多尺度性质的数据覆盖范围，同时保持模型分辨率在每个尺度水平。本文应用新的综合方法研究了喜马拉雅-青藏造山带下P波和S波速度（δlnVP和δlnVS）的三维变化。特别地，我们能够通过δln（VP/VS）来约束泊松比的变化。该公式自然是数据自适应的，只有当所需的数据收敛可用时，才能在每个尺度上解析特征。首先出现的长波特征是一个明显的高δlnV异常，它在拉萨山脉北方边缘以外的一些地方延伸了500多公里。再往北，在西藏北方最近发生火山活动的区域下面有一个强烈的负异常。负δln（VP/VS）区域描绘了一个板状的近水平特征，集中在100-250 km深度之间。这些特点是一致的概念，化学难熔，因此浮力，地幔岩石圈的印度盾（“大印度”）已推进近水平向北远远超出了班公湖怒江缝合线。在地壳中，藏南隆格活动裂谷和亚东-古鲁活动裂谷沿着存在两个相互隔离的δlnV低区，深度均在100 km左右。深穿透裂谷意味着只有有限的水平位移被容纳在近垂直结构上。
[1] We discuss an innovation in traveltime tomography that combines wavelet-based, multiscale parameterization and finite-frequency theory to solve two outstanding issues that inevitably arise from uneven source station distributions and from the three-dimensional (3-D) nature of wavefront healing: how to objectively address the intrinsically multiscale nature of data coverage while simultaneously maintain model resolution at each scale level. We apply the new, integrated methodology to investigate 3-D variations of P and S wave speeds (δlnVP and δlnVS) beneath the Himalayan-Tibetan orogen. In particular, we are able to constrain variations in the Poisson's ratio via δln(VP/VS). The formulation is naturally data adaptive, resolving features at each scale only if the required data converge is available. The very first, long-wavelength feature that emerges is a clear anomaly of high δlnV that extends over more than 500 km beyond the northern edge of the Lhasa terrane at places. Farther northward, a strong negative anomaly underlies the region where recent volcanism occurs in northern Tibet. Regions of negative δln(VP/VS) delineate a slab-like, subhorizontal feature concentrated between depths of ∼100–250 km. Such characteristics are consistent with the notion that chemically refractory, and therefore buoyant, mantle lithosphere of the Indian shield (“Greater India”) has advanced subhorizontally northward far beyond the surficial Bangong-Nujiang suture. In the crust, two isolated regions of low δlnV, each extending to depths near 100 km, occur along the Lunggar and the Yadong-Gulu active rifts in southern Tibet. Deep penetrating rifts imply that only a limited amount of horizontal displacement is being accommodated on subvertical structures.