Studies of noise and signals from the Hagfors sub-array for array configuration design

The signal and noise correlation as a function of sensor separation is studied. By means of the correlation values the beamgain is calculated for different array configurations. Thus, the optimal array configuration for different number of seismometers can be found. The nine seismometers offer 36 different sensor combinations ranging from 194 to 2206 m resulting in 36 cross correlation values. For all the frequency bands the noise correlation curves show a negative minimum before tending to zero at larger sensor separations. The signal correlations are calculated by means of two nuclear explosions conducted in east Kazakhstan at the Soviet test site. Only the P-phase is studied. The Hagfors sub-array with 6 seismometers and the aperture of 1000 m has a beamgain of 6.3 decibels at 1.5 4.0 Hertz. The Hagfors sub-array correlation curves are compared to the corresponding curves from the seismological stations Noress in Norway and Finesa in Finland. The noise correlation curves intersect zero at smaller distances. The negative minima of the curves are approximately as small as the Noress ones while the Finesa minima without exception are smaller.