Using PKiKP coda to study heterogeneity in the top layer of the inner core

Abstract:

Significant lateral variations of the inner's core properties, such as the large-scale hemispherical pattern, have been confirmed by a variety of seismological observations. However the details of more regional variations are unclear. The Earthscope Transportable Array (TA), which is composed of nearly 2000 stations, and the Caltech Regional Seismic Network (CI) provide us an excellent opportunity to detect the properties of the inner core underneath the inner core's “western” hemisphere

 We have collected seismograms from both the TA and CI networks for more than 1000 earthquakes in the Americas with magnitude greater than 5.5 around U.S. which took place after 2002. This enabled us to find more than 40 events with clear PKiKP observations. These PKiKP observations are used to constrain the properties of the top layer of the inner core and the coda signal of PKiKP is also present in the data. PKiKP coda provides useful information about the small scale heterogeneity in the top layer of the inner core which is likely to be the region most strongly affected by of present-day inner core dynamical processes. The distance for these PKiKP observations ranges from near-podal to 95 degrees. In agreement with in previous studies we find inner core scattering (ICS), which causes strong PKiKP coda, in the distance range 45-75 degrees. However, the ICS we observe in these 40 western hemisphere events might be much weaker than the reported estimations. These differences may show the regional variations of the inner core properties and indicate more complex dynamical processes of the core.