High attenuation is another prominent global feature of the inner core (Widmer et al. Large-scale anisotropy in the inner core has been confirmed by using studies of normal modes (Tromp 1993 Durek & Romanowicz 1999) and PKP body wave traveltimes (Creager 1992), but the possible effects of mantle structure on PKP traveltimes are still under debate, especially the polar PKP paths with the strongest anisotropy from the South Sandwich Islands earthquakes (Leykam et al. Based on global data sets, large-scale seismic features of the inner core have been revealed by seismic waves. ![]() ![]() Most of our information about core structure is from seismology and a range of features have been revealed by seismologists in the last few decades (for recent reviews, see Deuss 2014 Tkalčić 2015). Additionally, studying its structure is also helpful to understand the features of magnetic field and then to predict its possible changes in the future (Glatzmaier & Roberts 1995).Ĭompared to the relatively uniform fluid outer core, the inner core, especially its upper layer, has a complex structure and attracts a great deal of interest (e.g. It is therefore of interest to study the seismic structure of the core in order to understand its formation and evolution. Cooling of the core results in the growth of the inner core at the ICB and this process contributes energy to power the dynamics of the Earth (e.g. The ICB, separating the solid inner core and liquid outer core, plays an important role in whole Earth dynamics and the maintenance and temporal variation of the magnetic field. The Inner Core Boundary (ICB) is one of the major interfaces in Earth's interior. Combining our clear observations with previous studies suggests either a hemispherical difference, or a regional variation, of small-scale heterogeneity in the inner core.Ĭore, outer core and inner core, Composition of the core, Body waves, Coda waves, Wave scattering and diffraction 1 INTRODUCTION Comparing our observations with numerical simulations, we conclude that this relatively weak ICS indicates small-scale heterogeneity in at least the top layer of the inner core beneath Central America. However, the ICS we observe in these 21 western hemisphere events is weaker than previously reported for the eastern hemisphere. In agreement with previous studies, inner core scattering (ICS), resulting in clear PKiKP coda, is found at epicentral distances of 60°–95°. We use seismic stations in the North America, including the Earthscope Transportable Array, to look at PKiKP and its coda waves. However, most previous observations sampled the inner core beneath the Pacific Ocean and Asia, often in the inner core's ‘eastern hemisphere’. ![]() Studies of these small-scale heterogeneities can provide critical information, such as the degree of alignment of iron crystals, the presence of possible partial melt and the grain size of iron crystals, all of which can be used to constrain the dynamic processes of the inner core. Small-scale volumetric heterogeneity has been detected in the top layer of the inner core by PKiKP coda observations. However it is still unclear which dynamic processes in the core are responsible for these variations. Significant lateral and depth variations of the inner core's properties, such as the large-scale hemispherical pattern, have been confirmed by a variety of seismological observations.
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