High-Resolution Crustal Imaging in South-Central Alaska Across the Denali Fault with Dense Geophone Deployment and Beamforming

Abstract:

Between February and March of 2019, we deployed a dense semi-linear array of 306 three-component nodal geophone stations in south-central Alaska across the Denali Fault with ~1 km spacing. Combined with data from Alaska Regional Network, the US Array, and the FLATS Array, we calculate multi-component noise cross-correlations to extract Rayleigh wave phase velocities between 5 and 12 sec period using a beamforming method. The resulting phase velocity profile with 15 km lateral resolution shows strong changes in seismic velocity across all of the major fault zones in central Alaska including the Denali, Hines Creek, Northern Foothills, and Talkeetna Faults. The strongest velocity contrast is observed across the Hines Creek fault – the major boundary between the Wrangellia and Yukon Composite Terranes – with the North side having nearly 30% lower velocity than the South at 6s to 10s periods. The Denali fault is expressed as a low velocity zone with consistent ~20% reduction in velocity at periods 5s to 11s and faster velocities to the South of the fault. We are currently performing piece-wise 1D inversions to map changes in seismic velocity to depth and the final 2D shear velocity model across the array will be summarized and presented.