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

研究人员建议对下地幔不连续层进行全面搜索，方法是利用全球两个全球和一个区域地震台网中约450个宽带地震台站以及两个大型便携式地震阵列记录的数万张地震记录。大约7万张具有强P（或P_diff）到达的三分量、震源归一化地震图将被用来通过叠加P- S转换相位来成像不连续体，大约2.5万张具有强SS到达的震源归一化地震图将被用来通过叠加震源-接收路径中点的底部反射S波来研究不连续体。将叠加相同数量的合成地震图以验证结果。通过叠加全球数字地震台网记录的约20,000个P-to-S接收函数，初步工作揭示了1100、1600、2000、2450和2650 km深度可能存在的不连续。这些不连续面的叠加振幅约为P410S的1/6 ~ 1/2，这意味着这些明显不连续面的速度差在1 ~ 2%之间。建议的工作包括：利用3倍以上的数据来改进初步观测，通过叠加SS前兆和使用合成地震记录来补充和验证P-to-S结果，通过叠加小盖头的P-to-S转换和SS前兆来映射下地幔不连续性的空间变化，最后通过建立网络数据库，将处理后的约10万个三分量宽带地震记录公开

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.--