Characterizing the lithosphere-asthenosphere boundary in southern and eastern California

Beth Shallon, & Heather A. Ford

Published September 11, 2022, SCEC Contribution #12228, 2022 SCEC Annual Meeting Poster #262 (PDF)

The thickness of the lithosphere in the western United States has been found to be thinner than that of the stable continental interior of North America. Explanations for this thin lithosphere range from active tectonics to the presence of partial melt in the asthenosphere. While regional variations appear robust, it is less clear how lithospheric thickness estimates vary based on seismic imaging methods, such as receiver function analysis and surface wave tomography. Crucially, estimates of lithospheric thickness are used as inputs for the SCEC Community Thermal Model (CTM), which is used as an input in the SCEC Community Rheology Model (CRM). Therefore, understanding whether systematic differences in observed lithospheric thickness estimates exist between methods may help us to better understand the uncertainties in the SCEC community models.

To better understand how constraints on lithospheric thickness vary between receiver functions (RF) and surface wave tomography, we first calculated Sp receiver functions using data from over 1000 broadband stations from more than 50 temporary and permanent networks from across the southwestern U.S. We find the average depth of the lithosphere-asthenosphere boundary (LAB) phase across our study area to be 65.3 km, but absolute depths vary from roughly 30 to 100 km. Here, we focus our presentation on the depth of the LAB phase beneath southern and eastern California, divided into sections based on the physiographic boundaries of Fenneman and Johnson (1946) in order to understand the potential relationship between the depth of the LAB phase and tectonics.

Lastly, we compare depth picks of the LAB from Sp RF to the surface wave tomography model of Shen and Ritzwoller (2016) to assess if, and to what extent, our interpretation of the LAB correlates with features of their model. Across the study area, roughly 80% of the RF LAB depth picks fall within the depth range of negative velocity phase determined from tomography, suggesting a coarse agreement between methods in most locations. However, no correlation exists between RF LAB depth and other aspects of the tomography model, such as the depth of the maximum negative velocity gradient, or the maximum or minimum velocity depths. Ongoing work is being done to better understand the differences in seismic constraints of the LAB and resulting mantle structure, which can then be used to improve the CTM and CRM.

Citation
Shallon, B., & Ford, H. A. (2022, 09). Characterizing the lithosphere-asthenosphere boundary in southern and eastern California. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)