Migration Imaging of Mid-Upper Mantle Discontinuities

研究人员建议使用宽带Ps和其他分散的地震波相位来更好地对中上地幔的地震速度不连续性进行成像。 它们将侧重于150-400公里深度范围内的结构，在那里观察到了各种各样的不连续结构。 这些功能的起源可检验的假设包括：从位错蠕变扩散蠕变的过渡，层的流变学薄弱，由于挥发物富集，层的部分熔融，大陆岩石圈内的机械边界，和矿物相变。 不同的机制意味着不连续性的深度，极性，强度和各向异性的属性的差异，这些预测中的一些不同的构造环境，由于地幔温度的变化。 这些预测将与全球观测到的不连续结构（使用IRIS/全球地震网络台站）进行比较，并与大陆板块、活跃变形大陆区域、俯冲带和大洋中脊下的重点区域研究进行比较（使用PASSCAL实验和其他阵列的数据）。 将采用两种类型的偏移：通过对来自不同地理或后方位角箱的数据进行同时反褶积来确定接收器功能，以及正式的2D偏移。接收器函数合并作为后方位角的函数在解决各向异性方面特别有效，并且所提出的2D偏移具有很大的潜力来约束不连续处的P波和S波速度对比。 这项工作将有助于表征中上地幔流变学、变形机制、各向异性组构以及挥发分和熔体分布。

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.