Migration Imaging of Mid-Upper Mantle Discontinuities

研究人员提出利用宽带Ps和其他分散的远震相位更好地成像中上部地幔的地震速度不连续。他们将把重点放在150-400公里深度范围内的结构上，在那里已经观察到丰富多样的不连续结构。这些特征起源的可验证假设包括：从位错蠕变到扩散蠕变的转变，由挥发性富集引起的流变弱层，部分熔融层，大陆岩石圈内的机械边界，以及矿物相变。各种机制暗示了不连续深度、极性、强度和各向异性性质的差异，并且由于地幔温度的变化，这些预测在不同的构造环境中有所不同。这些预测将与全球观测到的不连续结构进行比较（使用IRIS/全球地震台站），并与大陆克拉通、活跃变形的大陆区域、俯冲带和洋中脊下方的重点区域研究进行比较（使用来自pascal实验和其他阵列的数据）。将采用两种类型的迁移：通过同时对来自不同地理或反向方向的数据进行反卷积来确定接收函数，以及正式的二维迁移。接收函数合并作为反向方位的函数在解决各向异性方面特别有效，并且所提出的二维偏移具有很大的潜力来约束不连续处的纵波和横波速度对比。这项工作将有助于表征中上部地幔流变学、变形机制、各向异性结构以及挥发性和熔体分布。

FischerEAR-0208284The investigators propose to better image seismic velocity discontinuities in the mid-upper mantle using broadband Ps and other scattered teleseismic phases. They will focus on structure in the 150-400 km depth range, where a rich variety of discontinuity structures have been observed. Testable hypotheses for the origin of these features include: the transition from dislocation creep to diffusion creep, layers of rheological weakness due to volatile enrichment, layers of partial melt, mechanical boundaries within the continental lithosphere, and mineralogical phase transformations. The various mechanisms imply differences in discontinuity depth, polarity, strength and anisotropic properties, and some of these predictions vary between tectonic environments due to changes in mantle temperature. These predictions will be compared to observed discontinuity structure globally (using IRIS/Global Seismic Network stations), and with focused regional studies in continental cratons, actively deforming continental regions, subduction zones, and beneath a mid-ocean ridge (using data from PASSCAL experiments and other arrays). Two types of migration will be employed: determination of receiver functions by simultaneous deconvolution of data from different geographic or back-azimuth bins, and formal 2D migration. Receiver function binning as a function of back-azimuth is particularly effective at resolving anisotropy, and the proposed 2D migration has great potential to constrain both P-wave and S-wave velocity contrasts at discontinuities. This work will help to characterize mid-upper mantle rheology, deformation mechanism, anisotropic fabric, and volatile and melt distributions.