Introduction

When the arrays came into routine operation the focus of research shifted from the design of the arrays and the recording systems to the analysis and interpretation of the SP body-wave (principally P) seismograms. With such high-quality recordings (on which local effects are suppressed) with the flexibility to change the playout speeds and magnification, routine analysis (the measurement of times, polarities, A and T) could be carried out with less error than on conventional paper and photographic recordings. The development of ways of increasing the bandwidth of SP recordings and correcting for the effects of attenuation further improved methods of analysis. But, whereas such improvements are valuable, there had to be more that could be learnt from array seismograms than this; and this proved to be so, for with the aid of the programs to synthesize seismograms, progress began to be made with the detailed interpretation of array recordings. An hypothesis about some feature of a seismogram could be tested by setting up the appropriate model and comparing the synthetic seismogram with the observed one. Synthesizing seismograms can also be used to explore the effects of variation in source and Earth models to answer the question ‘What would be the effect of…?’.