Testing the utility of S receiver function analysis for mapping seismic discontinuities in the Sierran lithosphere.

摘要

Existing geologic, geodynamic, geochemical and geophysical evidence suggest that incipient lithospheric delamination of the Cretaceous Sierra Nevada batholith is responsible for the disappearance of its dense residual eclogitic root (Zandt et al., 2004). Lithospheric delamination may be an effective, widely occurring mechanism for both lithospheric thinning and the production of overall intermediate crust from a mafic mantle, processes that have long puzzled geologists (Bird et al., 1979; Zandt et al., 2004). In order to better understand this enigmatic process, the Sierra Nevada EarthScope Project deployed a two phase, broadband seismic array consisting of 95 sites spaced nominally at 25 km from 2005-2007. Seismic investigations using these and previously collected data reveal fine-scale, complex lithospheric seismic structure beneath the Sierra associated with the delamination process (Zandt et al., 2004; Frassetto et al., 2009).;The experimental S receiver function technique utilizes teleseismic S and Sp converted phases to map lithospheric seismic discontinuities. Though the method has been successfully implemented using large datasets from long-term deployments, few successful detailed studies exist for short-term deployments in regions of fine-scale, complex seismic structure such as the Sierra (Yuan et al., 2006; Li et al., 2007). In this study, we conduct S receiver function analysis of SNEP, EarthScope/USArray Transportable Array and Berkeley Digital Seismic Network data in order to test the potential utility of this technique in mapping seismic discontinuities of the Sierran lithosphere for implications on delamination. Efforts focus primarily on imaging the topography of the Sierran Moho to bolster recent P receiver function findings and detecting the Sierran basal low velocity zone, which often characterizes the lithosphere-asthenosphere boundary. We observe discontinuities broadly consistent with P receiver function results and delamination structures, however resolution considerations and other limitations inherent to the method preclude independent interpretation.