Sp receiver function analysis further constraining the physical properties of the lithosphere-asthenosphere boundary within the southwestern United States

The lithosphere of the western United States has been found to be thinner than that of much of the contiguous US; associated slow seismic wave speeds are thought to be indicative of the presence of partial melt in the region. However, the discussion around the amount and distribution of melt, as well as the relationship between mantle wave speeds and surface volcanism, is ongoing. The purpose of this study is to provide an updated characterization of the lithosphere-asthenosphere boundary (LAB) across California and Nevada using Sp receiver functions combined with detailed comparisons to seismic tomography models. To better understand the physical properties of the LAB in the western US, we begin by calculating single-station and common-conversion-point stacked (CCP) Sp receiver functions using data from over 1000 broadband stations from more than 50 temporary and permanent networks, ranging from 31°N to 43°N and 112°W to 126°W. In our analysis we use an extended time multi-taper cross-correlation method and depth migrate using the 1D velocity model AK135. The receiver functions are then stacked for both single stations as well as for common conversion points (CCP) over the volume of the study area, as described in Lekic et al. 2011. CCP stacked receiver functions are then plotted and compared to earlier work. We are particularly interested in the shallower than expected LAB beneath parts of Walker Lane and variations in thickness beneath the Mojave Block, both of which may be related to recent volcanism or other tectonic processes. Preliminary results from the CCP stacking image the LAB at depths shallower than 100km depth. This shallow LAB depth generally agrees with previous studies (i.e., Lekic et al. 2011, Ford et al. 2014). Throughout the whole region, the LAB has discontinuities due to its evolving thickness, and because the LAB is an interface interpreted as a velocity gradient rather than a velocity step. In the future we intend to more accurately characterize the properties of the LAB using our calculated Sp receiver functions by forward model synthetic receiver functions to determine the best fitting velocity gradient for the LAB and comparing these results to previously published tomography models.