Seismo Lab Brown Bag Seminar

Repeating earthquakes offer a unique window into the temporal evolution of deep Earth. These events generate nearly identical seismic waves, allowing for the detection of subtle changes in the inner core (IC) and core-mantle boundary (CMB), both critical for understanding the Earth's internal dynamics.

There has been a long-standing controversy over the inner core's behavior for the past 30 years. Our analysis of 121 earthquake pairs from the South Sandwich Islands (1991–2023) recorded by the Eielson (ILAR) and Yellowknife (YKA) arrays, reveals that the inner core experienced periods of faster and slower rotation relative to the Earth's mantle. Extending this analysis, we found non-rotational changes at YKA between 2004 and 2008, indicating deformation near the shallow inner-core boundary. These findings point to both rotational and localized processes, likely driven by boundary topography and interactions with mantle and outer-core forces.

We further investigated temporal variations near the CMB using the same repeating earthquake data. We examined scattered waves from diffracted P and PKP precursor phases recorded at Alice Springs and YKA seismic arrays. Despite the high sensitivity of these waves, no significant changes were observed, suggesting that dynamic processes at the CMB may be too subtle to detect or occur on different timescales.