Seismic P wave

Behn M. D. and Kelemen P. B. (2003) The relationship between seismic P-wave velocity and the composition of anhydrous igneous and meta-igneous rocks. Geochem. Geophys. Geosys. (4)1041, doi 10.1029/2002GC000393. 

Shaw et al, 1994), the Baltic Shield (Joeleht and Kukkonen, 1998), and the Indian Shield (Roy and Rao, 2000). Nevertheless, these efforts remain limited to a few exceptional areas (Rudnick and Fountain, 1995). One outstanding problem is that the lowermost crust cannot be sampled directly, except perhaps in the Ivrea Zone, Italy, or in the Kohistan arc, Pakistan (Miller and Christensen, 1994). In seismic Shield models, the lowermost crust, identified by seismic P-wave velocities in the range 6.8-7.2kms makes up 16 km out of 45 km of the crustal column (Durrheim and Mooney, 1991 Christensen and Mooney, 1995). This large fraction of the crust remains elusive. 

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