Notes on the variability of reflected inner core phases
Dunzhu Li1, Daoyuan Sun2, Don Helmberger1
1 Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA 2 Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA
Notes on the variability of reflected inner core phases
Dunzhu Li1, Daoyuan Sun2, Don Helmberger1
1 Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA 2 Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA
摘要Recent events beneath Central America have produced excellent sets of inner core reflection (PKiKP phase) at high frequency recorded by USArray ranging from 18 to 30. However, the amplitude of this phase displays considerable scatter with a factor of six or more. Such scatter has been attributed to upper-mantle scattering and the Inner Core Boundary (ICB) in combination. Here, we show that neighboring events share upper-mantle scatterers beneath the receivers, and their ratio allows a clearer image of deep earth structure. After confirming some of the measured variation is indeed due to deep structure, we stacked nearby traces to reduce fine scale variations which are mostly due to shallow structure. Then, the remaining relatively large scale variation pattern of PKiKP phase is caused by the inner core boundary, as demonstrated by numerical experiments. After migration of data to the ICB, we observe a consistent image. We find such a pattern can be explained by a patch of mushy material of a few kilometers high where the material changes gradually from that of the outer core to that of the inner core.
Abstract:Recent events beneath Central America have produced excellent sets of inner core reflection (PKiKP phase) at high frequency recorded by USArray ranging from 18 to 30. However, the amplitude of this phase displays considerable scatter with a factor of six or more. Such scatter has been attributed to upper-mantle scattering and the Inner Core Boundary (ICB) in combination. Here, we show that neighboring events share upper-mantle scatterers beneath the receivers, and their ratio allows a clearer image of deep earth structure. After confirming some of the measured variation is indeed due to deep structure, we stacked nearby traces to reduce fine scale variations which are mostly due to shallow structure. Then, the remaining relatively large scale variation pattern of PKiKP phase is caused by the inner core boundary, as demonstrated by numerical experiments. After migration of data to the ICB, we observe a consistent image. We find such a pattern can be explained by a patch of mushy material of a few kilometers high where the material changes gradually from that of the outer core to that of the inner core.
收稿日期: 2013-12-28
出版日期: 2014-08-08
基金资助:NSF EAR-1053064 and CSEDI EAR-1161046 at CalTech with partial support of D. Sun at USC under EAR-0809023
通讯作者:
Dunzhu Li
E-mail: lidunzhu@gmail.com
引用本文:
Dunzhu Li, Daoyuan Sun, Don Helmberger. Notes on the variability of reflected inner core phases[J]. 《地震学报》英文版, 2014, 27(4): 441-468.
Dunzhu Li, Daoyuan Sun, Don Helmberger. Notes on the variability of reflected inner core phases. Earthquake Science, 2014, 27(4): 441-468.