Shear-wave structure of the lithosphere above the Hawaiian hot spot from two-station Rayleigh wave phase velocity measurements

We have measured fundamental mode Rayleigh wave phase velocity dispersion f rom seismograms of five earthquakes recorded at stations on the islands of Hawaii and Oahu and inverted these data for upper mantle velocity structure . The seismic lithosphere of the velocity model is 88+/-7 km thick, which i s similar to that of 80-90 Myr oceanic lithosphere, indicating that no sign ificant lithospheric thinning takes place above the mantle plume. Below the lithosphere the shear wave velocity decreases to similar to 4.0 km s(-1). The seismic model is consistent with the structure of-the Hawaiian plume mo del of Watson and McKenzie [1991] which has a 72-km thick mechanical bounda ry layer with the shallowest melting occurring at 82 km depth. The differen ce between the dispersion measured on the Hawaii-Oahu path and that observe d by Woods and Okal [1996] on the Oahu-Midway path can be explained by the cooling of the injected hot plume material.