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

研究人员建议利用全世界两个全球地震台网和一个区域地震台网中约450个宽带地震台站记录的数万张地震图以及两个大型便携式地震台阵，对下地幔不连续性进行全面搜索。大约70，000个三分量，震源归一化地震图具有强P（或P_diff）到达将用于通过堆叠P到S转换的相位来对不连续性成像，并且大约25，000个具有强SS到达的震源归一化地震图将用于通过在震源中点处叠加底侧反射S波来研究不连续性，将叠加相同数量的合成地震记录以验证结果。通过叠加全球数字地震网络记录的大约20，000个P-to-S接收器函数的初步工作，揭示了1100、1600、2000、2450和2650 km深度处的几个可能的不连续性。这些结构面的叠加振幅约为P410 S的1/6 ~ 1/2，表明这些结构面的速度差约为1/2%。通过叠加P-S转换和小盖层中的SS前兆来绘制下地幔不连续性的空间变化，最后通过建立一个基于网络的数据库，将处理后的大约10万个三分量宽带地震图公之于众。

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.--