Description
Reflection imaging allows high imaging resolutions for targets inside the Earth. But imaging the deepest targets, like the Earth’s inner core, is impossible with active sources at the surface due to the required huge source power. Seismic interferometry (SI) with ambient noise and/or global earthquakes has allowed retrieval of virtual reflections from such deep targets. Retrieval of non-physical (ghost) arrivals with SI has allowed even closer look at the Earth’s deeper targets, but so far there have been no attempts to retrieve virtual zero-offset reflections from inside the inner core for describing changes in its velocity and/or boundary topography. We apply SI to global earthquakes to retrieve ghost zero-offset reflections from inside the inner core only, i.e., zero-offset reflections that would be recorded if a pulse-echo experiment were performed by placing an instrument directly at the inner-core boundary. The dataset, recorded in Spain and Morocco by PICASSO, contains several PKIKP phases from global earthquakes with epicenters close to diagonally in relation to PICASSO. We apply SI to each of these PKIKP phases to correlated them with their internal multiple through the inner core – PKIIIKP phases. We do this for each PICASSO station resulting in a correlation panel per phase and stack it per phase to improve the signal-to-noise ratio and retrieve the final ghost zero-offset reflection from inside the inner core. We interpret our results comparing them with calculated two-way traveltimes of expected zero-offset reflections using the AK135 model. For some of the phases, the retrieved ghost zero-offset reflections indicate differences with the AK135 model that would mean inner-core boundary topography at least twice larger than suggested in previous studies. Thus, we interpret such results as indicating velocity difference inside the inner core, along the ghost zero-offset reflection ray path, compared to the AK135 model extra to possible detected topography. For other phases, the retrieved ghost zero-offset reflections indicate differences with the AK135 model that are comparable to or smaller than explainable with possible topography. We interpret such result as indicating detected low inner-core boundary topography and/or small velocity differences with the AK135 model.| Period | 13 Dec 2022 |
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| Event title | AGU Fall Meeting 2022 |
| Event type | Conference |
| Location | Chicago, United StatesShow on map |
| Degree of Recognition | International |