Phase velocities from seismic noise using beamforming and cross correlation in Costa Rica and Nicaragua

An expression for the cross correlation of noise between seismic stations and the 2D Green's function is derived assuming that noise travels as 2D surface waves. The phase velocity is obtained directly from the noise correlation function with a phase shift of +pi/4. Mean phase velocity dispersion curves are calculated for the TUCAN seismic array in Costa Rica and Nicaragua from ambient seismic noise using two independent methods, noise cross correlation and beamforming. The noise cross correlation and beamforming methods are compared and contrasted by evaluating results from the TUCAN array. The results of the two methods as applied to the TUCAN array agree within 1%, giving good confidence in the phase velocities extracted from noise.