Searching for Mid-Mantle Water with Multitaper-Correlation SS Precursors
Abstract
Earths mantle transition zone (MTZ) is a possible global water reservoir and may be responsible for long-term (~100 Ma) ocean-mass regulation, driven by plate tectonics and mantle convection. Estimates of MTZ mineral water capacity are ~1 wt %, far greater than that of rocks of either the upper or lower mantle. When water-rich material from the transition zone penetrates the upper or lower mantle, partial melting occurs due to the decrease in water capacity after phase transition, generating a reduction in seismic velocities. This process can add an additional low-velocity interface that can be imaged above(below) the 410(660)-km discontinuities, if melt is present. Seismic receiver functions have detected velocity reductions both above and below the mantle transition zone, interpreted to be partial melting induced by high water content, under the Alpine orogeny, in the deep Japan-slab subduction zone, and the western United States. Here, we conduct a global survey for seismic low-velocity zones (LVZs) both above and below the MTZ using SS precursors. Detection and interpretation of LVZs surrounding sharp positive-velocity gradients, such as the 410-km or 660-km discontinuity, is often complicated by side lobes, an artifact of popular signal processing routines. To address this challenge, we estimate SS precursors via the multitaper-correlation (MTC) technique. MTC allows for analysis at higher frequency, leading to finer resolution, and can increase the number of useful data records. The precursors to the SS phase reflect off interfaces near the source-receiver midpoint, so seismic stations are not required to be located near the target region. Here, we conduct MTC SS-precursor analysis for seismic waveforms recorded on the ~125 stations of the Global Seismographic Network and other permanent networks. Results will be compared to LVZs interpreted from previous RF analysis.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMMR25A0064F