Abstract

The small-aperture array NORESS in southern Norway was designed to detect phases from events at regional distances (up to 2000 km). In addition, this array has shown an excellent ability to detect teleseismic events.

This study has been conducted to determine the achievable P-phase SNR (signal-to-noise ratio) gains at various frequencies. It has been found that by carefully choosing the proper array subgeometry at different frequencies, gains exceeding 10 dB can be consistently achieved over almost the entire frequency band 0.5 to 10 Hz. The optimum subgeometries are as follows:

0.5 to 1.0 Hz:  AO, D ring (10 elements) 
1.0 to 2.3 Hz:  AO, C, D rings (17 elements) 
2.3 to 5.0 Hz:  AO, B, C, D rings (22 elements) 
5.0 to 10.0 Hz:  AO, A, B, C, D rings (25 elements, i.e., full array) 
0.5 to 1.0 Hz:  AO, D ring (10 elements) 
1.0 to 2.3 Hz:  AO, C, D rings (17 elements) 
2.3 to 5.0 Hz:  AO, B, C, D rings (22 elements) 
5.0 to 10.0 Hz:  AO, A, B, C, D rings (25 elements, i.e., full array) 

An assessment has also been made of the processing gains that could be achieved using arrays smaller than NORESS. Thus, for an intermediate array (comprising AO, A, B, C rings, i.e., 16 elements, 1.4 km diameter) gains exceeding 8 dB could be consistently achieved from 1.5 to 10 Hz. For a small array (AO, A, B rings, i.e., 9 elements, 0.65 km diameter), gains exceeding 6 dB could be achieved from 3 to 10 Hz.

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