Imaging Upper Mantle Discontinuities Using Stacking and Finite-Frequency Methods

Abstract:

Imaging fine structure of upper mantle can help to reveal the pattern of mantle convection and put constrains on the thermal and chemical conditions of the mantle. The topography of 410- and 660-km discontinuities, which bound the transition zone, are important in understanding the phase transform, the pressure-temperature condition and the compositional heterogeneities of the upper mantle. For tens of years, people have made great effort studying the existence and the characters of mantle discontinuities and have already had much understanding about the mantle discontinuities. And thanks to the advent of high-density network, we are now possible to scrutinize some parts of the earth with more data and get more specific results.

In our research, transverse component SS precursors are used to map the topography of the 410- and 660-km discontinuities. We stack the data in 5°×5° cap and produce global map of the 410- and 660-km discontinuities topography. We also measure SdS-SS traveltime residual from stacked waveforms and calculate finite-frequency sensitivity kernels to invert for the topography of 410 km and 660 km discontinuities. We use data from IRIS, ORFEUS and F-net and get more than 60,000 bounce points globally. Several regions around the world are sampled well including north Pacific Ocean, mid Atlantic Ocean and the Arctic, which makes it possible to investigate the transition zone under plumes, mid ocean ridge and around subduction zones.