Mantle Transition Zone Seismic Discontinuities Studied Globally using Dozens of Dense Temporary Seismic Arrays

Abstract:

Global studies of Mantle Transition Zone (MTZ) seismic structure have traditionally been approached by averaging observations from sparse (>1000 km instrument spacing), long-duration recordings from the Global Seismic Network. In comparison, we study MTZ seismic structure using dense (average instrument spacing of ~70 km) regional temporary arrays from various geodynamic and tectonic settings around the globe. We target open source seismic data where arrays include an average of ~55 stations recording for a minimum of 18 months. Our array-based approach provides improved source estimations for deconvolution and complementary spatial sampling compared to previous global studies. We access arrays since ~1995 across a range of settings including: hot spots, continent-continent and ocean-continent subduction, spreading ridges, rift margins, and cratons. Stacked teleseismic P-to-S receiver functions are calculated using multichannel spectral deconvolution and migrated to depth. Synthetic receiver functions are calculated using the reflectivity method with identical slowness sampling and processing applied to the synthetics as was applied to the observed receiver functions. Results show frequency-dependent amplitude for the 410-km and 660-km discontinuities in each region and a range of results for the 520-km discontinuity including regions where it is not observed. The regional velocity jump and sharpness of MTZ seismic discontinuities will be inverted for using a Markov Chain Monte Carlo approach. Inversion results will be compared to results from modern laboratory mineral physics experiments that test the effect hydration, olive content, and temperature can have on velocity at mantle pressures.