ESTIMATION OF CRUSTAL POISSONS RATIO FROM BROAD-BAND TELESEISMIC DATA

Knowledge of Poisson's ratio constitutes an important constraint on the physical properties of the continental crust. To date there are only a few locations in the world where direct measurements of this parameter have been made. In this paper we describe a single station technique for measuring crustal Poisson's ratio from the boundary interaction phases in broad band teleseismic waveforms. In principle we can derive an estimate from one seismogram, although in practice using several seismograms helps overcome the low signal to noise ratio of the boundary interaction phases. We apply our method to 6 North American stations using 9 deep focus earthquakes in various locations. By performing a nonlinear search for the optimum Poisson's ratio and Moho depth, we are able to make a stable estimate of Poisson's ratio in each case. The estimates range from 0.22 to 0.315, representing the extremes that are usually found on the North American continent. The low value at station COL (Fairbanks, AL). is corroborated by a refraction survey in the same region. Because of the small number of seismograms needed, this technique is especially well suited for portable teleseismic experiments. In addition, we will be able to obtain estimates at each of the 100+ permanent broad band stations that are to be shortly deployed, ensuring that the number of measurements of this important parameter can quickly increase by an order of magnitude.