High Resolution Imaging of Mantle Discontinuities across South America at 20 Degrees South

Kelly LiuEAR-0001000这项计划将对横跨南美洲中部的20度S纬线上3000公里长的剖面下的主要不连续面进行高分辨率研究。这项研究将利用一个独特的数据集，它是1992-1995年期间进行的三个便携式地震实验的宽带数据集的组合。752个高质量径向接收器函数的非线性叠加的初步结果表明，410和660个不连续面在整个剖面上都有明显的空间变化。一些有趣的特征包括：1)俯冲板块将660不连续面压低至少35公里，或长达65公里，2)安第斯山脉以西，莫霍面深度约40-45公里，但在不到50公里的距离内增加到65-80公里，并在安第斯山脉东部边界以下减少到约45-50公里，3)过渡带厚度约为海洋一侧250公里，大陆一侧260公里，表明前者比后者热，4)在300公里深度以上存在一组强烈的负到达，但只在大陆一侧的板块上方。这项研究将使用一套程序，如P-P-S和S-P转换的相位深度成像，在不连续面上的深源地震波转换，以及合成地震记录，以改进和扩展初步结果，并测量不连续面的其他性质的空间变化，如其锐度和速度对比度。这项研究将开发一种程序，从倾斜的界面叠加转换波，以直接绘制俯冲板块。

Kelly LiuEAR-0001000This proposal will conduct a high resolution study of the major discontinuities beneath a 3000 km long profile along the 20 degree S latitude line across central South America. The study will utilize a unique data set, which is a combination of broadband data sets from three portable seismic experiments conducted during 1992-1995. Preliminary results by non-linear stacking of 752 high quality radial receiver functions suggest clear spatial variations of both the 410 and 660 discontinuities across the profile. Some interesting features include: 1) the 660 discontinuity is depressed by at least 35 km, or as large as 65 km, by the subducting slab, 2) west of the Andes, the depth to the Moho is about 40-45 km, but it increases to 65-80 km over a distance of less than 50 km and decreases to about 45-50 km beneath the eastern boundary of the Andes, 3) the transition zone thickness is about 250 km of the ocean side, and 260 km on the continent side, indicating that the former is hotter than the later, and 4) there exists a group of strong negative arrivals above the 300 km depth, but only above the slab on the continental side. The study will use a set of procedures such as phasing depth imaging of P-to-S and S-to-P conversions, conversions of waves from deep local earthquakes at discontinuities, and synthetic seismogram to improve and expand the preliminary results, and to measure the spatial variations of other properties of the discontinuities such as their sharpness and velcoity contrast. The research will develop a procedure to stack converted waves from tilted interfaces to directly map the subducting slab.