Deep Seismic Crustal Structure Beneath Wallowa, Columbia River Flood Basalt Province

Date: 4/26/2019

Time: 04:45 PM

Room: Puget Sound

The Columbia River basalts (CRB) represent the largest volume of flood basalts associated with the Yellowstone hotspot, yet their source appears to be near the Wallowa Mountains, about 500 km north of the projected hotspot track (Hales et al., 2005). We extract teleseismic P-to-S converted phases from the temporary seismic linear-array to constrain deep seismic crustal structure in the source area of CRB eruptions. The dense, 160-km-long, N-S linear array covers an upper-mantle high-velocity anomaly that extends to ~225 km depth (Darold & Humphreys, 2013), and also a post-CRB bullseye pattern of topographic uplift with the Wallowa Mountains at the center. Receiver functions (RFs) and teleseismic migration provide enhanced sensitivity at localized velocity gradients across the lithospheric discontinuities. Preliminary images reveal a clear crust-mantle boundary shown as a single positive-polarity amplitude at 30-35 km depth at the southern and northern end of the seismic line. In the middle of the profile, where the seismic line crosses the bullseye topographic uplift (at 45.5°-46.5° latitude), we observe complex RF waveforms but mostly two positive-polarity amplitudes (at ~25 km and ~45 km depth), suggesting multi-layer structure interlaced with high and low velocities. The complexity in the waveforms indicates structural heterogeneities and/or anisotropy reflecting lithospheric interactions with the deep CRB magmatism.

Presenting Author: YoungHee Kim

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