3D transdimensional seismic tomography of the inner core

Inner core static tilt inferred from intradecadal oscillation in the Earth’s rotation

“…To explain the asymmetry between the inner core’s eastern and western hemispheres in seismological observations 42 , 43 , a previous dynamical model considers the crystallization and melting at the surface of the inner core and has similar suggestions 44 , i.e., the western hemisphere of the inner core is denser than its eastern hemisphere. Interestingly, a seismological study has suggested that the western hemisphere of the inner core may be relatively denser 45 , and a thicker compacting layer at the top of the inner core’s western hemisphere was also suggested 46 ; a more nuanced research found that the western zone is largely confined to the northern hemisphere 47 ; those suggestions are generally consistent with the westwards statically tilted inner core that we found.…”

“…Besides, the density jump of 0.52 ± 0.05 g/cm 3 at the ICB is also inverted based on the observed ICW period. Undeniably, it is difficult for seismological observations to detect such inner core static tilt directly, but interestingly, the results from seismological studies showed that the western/northwestern hemisphere (or at least its top layer) of the inner core may be relatively denser 42 – 47 . These suggestions, although they have some uncertainties, are qualitatively consistent with our finding of a westwards-tilted inner core, and we suggest such consistency should be helpful to the inner core oscillation or differential rotation.…”

Up-to-fivefold reverberating waves through the Earth’s center and distinctly anisotropic innermost inner core

“…Simultaneous observations of these exotic arrivals at regionally dense seismic networks opportunistically provide tools to constrain the IMIC properties because they sample the IMIC in an unprecedented fashion. Measurements from these observations, in agreement with recent independent findings 32 , 34 , 37 , 38 , confirm an anisotropically distinctive IMIC from the less anisotropic outer shell.…”

“…Note that a hemispherical structure of the IMIC has been suggested in two recent studies 38,62 . When inverting for the 3D structures of the IC using singlepassage PKIKP probes, the former study 38 found an IMIC confined in the eastern hemisphere with a slow direction at ~55 ± 16°. Our data sampling near the planetary center yields a similar value for the slow propagation direction.…”

An estimate of absolute shear-wave speed in the Earth’s inner core

“…Alternative from hcp as a candidate for stable crystallographic iron structures in the IC, bcc iron can also be stable in the IC condition 53,54 . Both hcp and bcc can explain distinct anisotropic properties of the innermost inner core, which was found seismologically to have a slow axis about 50-55°obliqued from the equator [55][56][57][58][59][60] . Additionally, the intrinsic properties of the bcc iron can explain the shear wave speed of 3.95 km/s 38 , which is just 3.5% higher than PREM values (Fig.…”