The use of arrays for earthquake seismology

Abstract

Abstract Several seismometer arrays are now being operated by the U.K. and U.S.A. for research connected with the detection of underground nuclear explosions. The processing techniques developed have proved to be valuable in the detection programme and, as they are equally applicable to earthquake seismology, some seismologists are already making use of the data obtained. The main factor likely to prevent general application is the cost of installing and of operating the array recording and analysis equipment. The cost of an array depends on many factors such as array design and site selection. These are discussed independently, and then three array systems of varying complexity are described and their relative cost and scientific capability compared. The first system consists of a single, close-spaced cluster of geophones, providing signal/ambient noise enhancement without the need for special analysis equipment. The second contains three clusters of geophones in a triangular configuration. This array, having dimensions comparable to the apparent signal wavelength, provides information about signal velocity and azimuth from the relative onset times. Triggered recorders are used to economize in the recording media and to minimize transcription and analysis time. The third system uses a large cross array, which permits beam-forming techniques to be used. This has the maximum scientific capability of the three methods, but requires a complex analysis facility. However, it is probable that earthquake seismologists will only require to analyse in detail a small percentage of the total number of events recorded, and can make use of a general purpose computer.