The youngest core tops with the highest sediment focusing factors are located in the Panama Basin. The ages range from 790 to over 15,000 years. Is the core top modern? Observations from the eastern equatorial PacificĪ compilation of ages from 67 core tops in the eastern equatorial Pacific (EEP) does not display an easily discernible regional pattern. For the ``western" hemisphere, on the other hand, W2 velocity gradient
A change of velocity gradient and Q value is required in the deeper portion of the inner core. For the ``eastern" hemisphere, the observations indicate that the E1 velocity gradient and Q structure, inferred from the PKiKP-PKIKP observations sampling the top 80 km of the inner core, extend at least to 230 km inside the inner core. We construct two seismic velocity and attenuation models, with one for each ``hemisphere", by iteratively modeling the observed PKiKP-PKIKP waveforms, the PKPbc-PKIKP differential travel times and the PKIKP/PKPbc amplitude ratios. The PKIKP/PKPbc amplitude ratios are generally smaller for those sampling the ``eastern" hemisphere. The PKPbc-PKIKP travel time residuals are about 0.7 second larger for those sampling the ``eastern" hemisphere than those sampling the ``western" hemisphere. The observed PKPbc-PKIKP differential travel times and PKIKP/PKPbc amplitude ratios exhibit an ``east-west" hemispherical difference. We choose recordings for events from 1990 to 2000 with simple source time functions, so only those of intermediate and deep earthquakes are used. We select PKPbc-PKIKP waveforms from recordings in the Global Seismic Network (GSN) and several dense regional seismic arrays. To answer this question, we combine the PKiKP-PKIKP dataset and the PKPbc-PKIKP observations at the distance range of 147o-160o to study seismic velocity and attenuation structures in the top 400 km of the inner core along the ``equatorial paths" (the paths whose ray angles > 35o from the polar direction). The question now arises as such to what depth this hemispherical difference persists. The PKiKP-PKIKP observations they used only allowed them to constrain the seismic structure in the top 80 km of the inner core. Recent seismic studies reveal an ``east-west" hemispherical difference in seismic velocity and attenuation in the top of the inner core. Seismic velocity and attenuation structures at the top 400 km of the inner core
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