Crustal structure of the New York-Pennsylvania area

Abstract

Phase velocities of Rayleigh waves in the period range from 15 to 45 seconds were determined from seismograms of the Waynesburg, Pennsylvania‐Ottawa, Ontario‐Palisades, New York, tripartite array. A theoretical model, compatible with these data and with previously published seismic refraction data of Katz, consists of a low‐velocity sedimentary layer overlying two crustal rock layers which in turn overlie the earth's mantle. The total crustal thickness is about 37 kilometers. Calculations of Rayleigh wave dispersion for a variety of theoretical models show that small variations in elastic properties from place to place may cause significant errors in the determination of total crustal thickness if such variations are neglected when the phase‐velocity method is used independently. The error is considerably less if supplementary data are used in conjunction with phase‐velocity data as was done in the example cited above.

Seismic Studies of the Earth's Crust in Continents I: Evidence for a Low-Velocity Zone in the Upper Part of the Lithosphere

“…Particularly significant is the fact that the observed group velocity maxima are very close to the results of theoretical dispersion computations for a model which includes the sialic lowvelocity layer. In N. America discrepancies greater than the uncertainty in the experimental values have been noted when comparison is made between surface wave dispersion data and theoretical calculations for models based on seismic refraction results (see, e.g., Press 1960, Oliver, Kovach & Dorman 1961, Dorman & Ewing 1962. In order to reconcile these two sets of observations, the surface wave method required either a lower average shear velocity for the crust or an improbably thick layer of sediments.…”