Receiver Functions

Receiver function imaging from broadband arrays (e.g., Fig. 6) provide detailed views of the crust and upper mantle, with sensitivity to the locations and velocity steps of major layers boundaries (e.g., Yuan et al. 2000; Bostock et al. 2002; Zandt et al. 2004; Nabelek et al. 2009; Levander et al. 2011; Lowry and Perez-Gussinye 2011 and many others). Early studies in the Cascades (Langston 1979) revealed many aspects of structure that remain unexplained; the largest interface appears at 15-20 km depth unlike regional Moho estimates of 30-35 km (e.g., Parsons et al. 1998; Buehler and Shearer 2010), and large tangential-component signals may indicate large crustal anisotropy, in many ways similar to images of mid-crustal magmatic bodies seen elsewhere (e.g., Zandt et al. 2003), and complementary to MT images (Hill et al. 2009). We will extend to 3D a variety of techniques to image the subsurface from teleseismic scattered waves used previously, including migration techniques (Rondenay et al. 2008; Abers et al. 2009; MacKenzie et al. 2010), array methods that detect laterally scattered signals (Abers, 1998) and single- station methods that incorporate dipping layers (e.g., Rossi et al. 2006). The proposed data set will be one of the first to allow fully three-dimensional unaliased sampling of interfaces from mid-crustal depths down to the slab (Fig. 6), allowing (for example) detailed maps of Moho structure and depth, identification and characterization of mid-crustal interfaces that may be associated with the top of the regional MT anomaly, and delineation of the slab and 3D variations in its surface impedance. Data from these images will: (a) map out major interfaces and their variations; (b) provide velocity information and Vp/Vs estimates, together with Ambient Noise Tomography, to test models of crustal differentiation (e.g., Calkins et al. 2010 Tatsumi et al. 2008); (c) identify potential large low-velocity zones to constrain the manner of magma storage; (d) identify possible mantle layering to evaluate petrologic models of the mantle wedge (e.g., Leeman et al. 2005). These analyses should also provide information on anisotropy, which has proven to be significant in the mid-to-lower crust in active settings (e.g., Zandt et al. 2003; Nikulin et al. 2009), and may reflect magma transport (Holtzman et al. 2003).

Figure 6.  Receiver-function ray density estimate for proposed array at depth of 15 km (left) and 100 km (right).