On the Nature of the P-Wave Velocity Gradient in the Inner Core beneath Central America  

作　　者：Hrvoje Tkali Thomas Bodin Mallory Young Malcolm Sambridge 

机构地区：[1]Research School of Earth Sciences, the Australian National University [2]Berkeley Seismological Laboratory, University of California at Berkeley

出　　处：《Journal of Earth Science》2013年第5期699-705,共7页地球科学学刊（英文版）

基　　金：Calculations were performed on the Terrawulf Ⅱ cluster,a computational facility supported through the AuScope Australian Geophysics Observing System(AGOS);Auscope Ltd.is funded under the National Collaborative Research Infrastructure Strategy(NCRIS)and the Education Investment Fund(EIF3),both Australian Commonwealth Government programmes

摘　　要：We conduct an experiment to investigate whether linearity in the observed velocity gradient in the volume of the inner core sampled by the PKP ray paths beneath Central America is a robust approximation. Instead of solving an optimization problem, we approach it within the Bayesian inference. This is an ensemble approach, where model specification is relaxed so that in- stead of only one solution, groups of reasonable models are acceptable. Furthermore, in transdimen- sional Bayesian inference used here, the number of basis functions needed to model observations is by itself an unknown. Our modeling reveals that in the ensemble of models, the most likely are those containing only 2 nodes （linear trend）. Thus our result justifies the assumption used for the deter- mination of inner core rotation with respect to the rest of the mantle that the observed gradient is constant in its nature （linear）. Recent observations in seismology suggest that it is likely that the spa- tial variability in elastic parameters is a widespread phenomenon in the inner core. Future array observations will further constrain spatial extent and magnitude of velocity changes and show whether there is a significant difference between these observations in the two quasi-hemispheres of the inner core.We conduct an experiment to investigate whether linearity in the observed velocity gradient in the volume of the inner core sampled by the PKP ray paths beneath Central America is a robust approximation. Instead of solving an optimization problem, we approach it within the Bayesian inference. This is an ensemble approach, where model specification is relaxed so that in- stead of only one solution, groups of reasonable models are acceptable. Furthermore, in transdimen- sional Bayesian inference used here, the number of basis functions needed to model observations is by itself an unknown. Our modeling reveals that in the ensemble of models, the most likely are those containing only 2 nodes （linear trend）. Thus our result justifies the assumption used for the deter- mination of inner core rotation with respect to the rest of the mantle that the observed gradient is constant in its nature （linear）. Recent observations in seismology suggest that it is likely that the spa- tial variability in elastic parameters is a widespread phenomenon in the inner core. Future array observations will further constrain spatial extent and magnitude of velocity changes and show whether there is a significant difference between these observations in the two quasi-hemispheres of the inner core.

关 键 词：solid earth physics deep geophysics. 

分 类 号：P31[天文地球—固体地球物理学]