Speaker: Sunyoung Park, University of Chicago

Mantle rheology is one of the least constrained properties despite its importance in mantle dynamics. This talk will introduce a novel approach for understanding the rheological structure by examining the Earth’s response to deep earthquakes occurring near the bottom of the upper mantle. A major challenge in utilizing the postseismic deformation from deep earthquakes lies in observation; to date, most GPS observations have been limited to shallow earthquakes since the amplitude of the surface deformation from deep events is relatively small. To overcome this, data processing techniques such as independent component analysis are utilized to examine the GPS data from the 2018 MW 8.2 Fiji earthquake, one of the largest deep earthquakes ever recorded, which occurred at ~560-km depth. This allows the detection of large scale, significant postseismic deformation in the first two years following the event. The overall directionality and amplitude of the deformation strongly suggest the presence of a rheologically weak structure atop the lower mantle. I will also discuss additional insights into mantle rheology and the influence of subducting slabs on viscoelastic relaxation.