Seismic velocity structure and composition of the continental crust: A global view

Abstract. Seismic techniques provide the highest-resolution measurements of the structure of the crust and have been conducted on a worldwide basis. We summarize the structure of the continental crust based on the results of seismic refraction profiles and infer crustal composi-tion as a function of depth by comparing these results with high-pressure laboratory measure-mentsof seismic velocity for a wide range of racks that are commonly found in the crust.. The thickness and velocity structure of the crust are well correlated with tectonic province, with extended crust showing an average thickness of 30.5 km and orogens an average of 46.3 km. Shields and platforms have an average crustal thickness nearly equal to the global average. We have coiTected for the nonuniform geographical distribution of seismic refraction profiles by estimating the global area of each major crustal type. The weighted average crustal thick-ness based on these values is 41.1 km. This value is 10 % to 20 % greater than previous esti-mates which underrepresented shields, platforms, and orogens. The average compressional wave velocity of the crust is 6.45 kmls, and the average velocity of the uppermost mantle (Pn velocity) is 8.09 kmls. We summarize the velocity structure of the crust at 5-km depth inter-vals, both in the form of histograms and as an average velocity-depth curve, and compare thes