Searching for Seismic Discontinuities in the Lower Mantle Using Broadband Seismic Data

EAR-0207466刘凯利研究人员建议利用全球两个全球地震台网和一个区域地震台网和两个大型便携式地震台阵的全球约450个宽带地震台站记录的数万张地震记录，全面寻找下地幔不连续。大约70,000条具有强P(或P_DIFF)到达的三分量归一化震源记录将被用于通过叠加P-to-S转换相来成像不连续性，而大约25,000条具有强SS到达的震源标准化记录将被用于通过在震源-接收器路径的中点叠加底部侧反射S波来研究不连续性。同样数量的合成地震记录将被叠加以验证结果。通过叠加全球数字地震台网记录的大约20,000个P-to-S接收器功能的初步工作，发现了1100、1600、2000、2450和2650公里深处可能存在的几个不连续面。这些不连续面的叠加幅度大约是P410S的1/6到1/2，这意味着这些明显不连续面上的速度差在1%到2%的量级。拟议的工作包括通过使用三倍以上的数据来改进初步观测，通过叠加SS前兆和合成地震图来补充和验证P-to-S结果，通过以小盘叠加P-to-S转换和SS前兆来绘制下地幔不连续面的空间变化图，最后通过建立一个基于网络的数据库来公布处理后的约10万个三分量宽带地震图。

EAR-0207466Kelly LiuThe investigators propose to perform a comprehensive search for lower mantle discontinuities by using tens of thousands seismograms recorded by about 450 broadband seismic stations worldwide in two global and one regional seismic networks, and two large portable seismic arrays. About 70,000 three-component, source-normalized seismograms with strong P (or P_diff) arrivals will be used to image the discontinuities by stacking P-to-S converted phases, and about 25,000 source-normalized seismograms with strong SS arrivals will be used to study discontinuities by stacking bottom-side reflected S waves at the mid-point of the source-receiver path. The same amount of synthetic seismograms will be stacked to verify the results. Preliminary work from stacking about 20,000 P-to-S receiver functions recorded by the Global Digital Seismic Network revealed several possible discontinuities at the depths of 1100, 1600, 2000, 2450, and 2650 km. The stacking amplitudes of those discontinuities are about 1/6 to 1/2 of that of P410S, implying that the velocity contrasts across those apparent discontinuities are in the order of 1 to 2%.The proposed work includes improving the preliminary observations by using three times more data, complementing and verifying the P-to-S results by stacking SS precursors and using synthetic seismograms, mapping spatial variation of lower mantle discontinuities by stacking P-to-S conversions and SS precursors in small caps, and finally, making the processed about 100,000 three-component, broadband seismograms public by establishing a web-based database.--