It has been suggested that a nonlinear, multi-channel summation process increases the signal-to-noise ratio of small coherent signals. Using the data base of the International Seismic Month, it is shown conclusively that a logarithmic beamforming process increases the detection probability for seismic events for a specified false alarm rate by at least a factor of two. A detector based on this process is working on-line at the Yellowknife seismic array.