Alteration of the Pacific Lithosphere and Asthenosphere by the Hawaiian Hotspot: A Re-Examination

Session: Advances in Seismic Imaging of Earth’s Mantle and Core and Implications for Convective Processes
Type: Oral
Date: 4/29/2020
Time: 09:30 AM
Room: 120 + 130
Description: 

We re-examine the shear velocity structure in the vicinity of the Hawaiian hotspot and Hawaiian swell using Rayleigh wave data from the PLUME project in the 20-125 s period range. We improve resolution and stability of the tomographic imaging by: removing tilt and compliance noise from the vertical component; using a higher sampling rate in the time series; equalizing resolution of phase velocity across all periods; beginning with an a priori crustal model based on receiver function analysis and topography; employing finite frequency kernels that use both phase and amplitude data; and iterating progressively from coarse resolution to finer resolution with the previous coarser model serving as a new starting model. With the noise removal, we have approximately 3600 seismograms at 100 s with good signal-to-noise compared to ~ 5200 at 50 s. In the phase velocity inversion with the multiple plane wave technique, we solve simultaneously for azimuthally averaged phase velocities, azimuthal anisotropy, coefficients describing the incoming wavefield, station amplitude corrections and attenuation. Median phase misfits are ~ 0.9s at 50-s period and 1.1s at 100 s.

In the upper lithosphere, there are shear velocity reductions of 5-10% in an area that is at least 200 km across trending parallel to the seamount chain. In the asthenosphere, there are lateral variations in velocity of similar amplitude, with minimum velocities of ~ 3.9 km/s reached at depths of 130-150 km. Anomalously low asthenospheric anomalies extend over a broader region, underlying essentially all of the Hawaiian swell. Asthenospheric attenuation is significantly greater than beneath either the East Pacific Rise or the Juan de Fuca spreading centers.

Presenting Author: Donald W. Forsyth

Authors