Seismic structure of the upper mantle across California and the offshore Borderland

A. Christian Stanciu, & Eugene D. Humphreys

Submitted August 15, 2020, SCEC Contribution #10757, 2020 SCEC Annual Meeting Poster #045

We present new P, S, and Vp/Vs seismic tomography models of the upper mantle across California and the Outer and Inner Borderland regions to improve our understanding of the regional tectonic evolution and current physical state of the upper mantle. Increased resolution in the Borderland region and northwestern California is achieved through the incorporation of additional data from the ALBACORE and Northern California experiments. We account for the crustal component by using the SCEC CVM crustal velocity model. Several technical improvements, including 3-D ray-tracing and azimuthal ray weighting, result in improved imaging of the upper mantle seismic anomalies. We resolve higher amplitudes and narrower structures compared to previous published models. For example, the Transverse Ranges and Isabella anomalies are reduced by approximately 10%. Beneath the Outer Borderland a high-velocity lower-amplitude structure is imaged. While this may be influenced by the incoming ray distribution or the presence of a deep offshore high-velocity structure, our synthetic modeling supports its existence at the present location. The southern end of Juan de Fuca is clearly imaged in the northern part of our model. Abandoned remnants of the Farallon slab, e.g. the descending Transverse Ranges high-velocity structure, drive southern California northward, contributing to rifting in the Salton Trough. Partial melting and high temperature could explain the low seismic structures in this region as a response to rifting processes.

Key Words
tomography, upper mantle, California, Borderland

Stanciu, A., & Humphreys, E. D. (2020, 08). Seismic structure of the upper mantle across California and the offshore Borderland. Poster Presentation at 2020 SCEC Annual Meeting.

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