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A seismic array is a system of linked seismometers arranged in a regular geometric pattern (cross, circle, rectangular etc.) to increase sensitivity to earthquake and explosion detection. A seismic array differs from a local network of seismic stations mainly by the techniques used for data analysis. The data from a seismic array is obtained using special digital signal processing techniques such as beamforming, which suppress noises and thus enhance the signal-to-noise ratio (SNR). The earliest seismic arrays were built in 1950s in order to improve the detection of nuclear tests worldwide. Many of these deployed arrays were classified until 1990s. Today they become part of the IMS as primary or auxiliary stations. Seismic arrays are not only used to monitor earthquakes and nuclear tests, but also used as a tool for investigating nature and source regions of microseisms as well as locating and tracking volcanic tremor and analyzing complex seismic wave-field properties in volcanic areas. == Layout == Seismic arrays can be classified by size, which is defined by its aperture given by the largest distance between the single seismometers. The sensors in a seismic array are arranged in different geometry pattern horizontally. The arrays built in early 1960s were either cross (orthogonal linear) or L-shaped. The aperture of these arrays ranges from 10 to 25 km. Modern seismic arrays such as NORES and ARCES are located on concentric rings spaced at log-periodic intervals. Each ring consists of an odd number of seismometer sites. The number of rings and aperture differ from array to array, determined by economy and purpose.〔 Take the NORES design as an example, seismometers are placed on 4 concentric rings. The radii of the 4 rings are given by: : If the three sites in the inner ring are placed at 36, 156 and 276 degrees from due North, the five sites in the outer ring might be placed at 0, 72, 144, 216 and 288 degrees. This class of design is considered to provide the best overall array gain. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Seismic array」の詳細全文を読む スポンサード リンク
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