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Extracted text: A seismic survey was carried out for a large project to determine the nature of the substrata. The results of the survey are given in Fig. i 2 in the form of a graph. Determine the depths of the strata. V, = 2250 m/sec x 5 x 10 C, V, Surface soil 6. V = 750 m/sec Sand and loose gravel V, Rock AB, = 8.75 x 10' sec AC, 33.75 x 1 sec AC: = 38.75 x 10 sec d; = 2.188 m dy = 22.5 m AB = 12.75 x 10 sec -V = 172 m/sec 20 d; Distance m 10 30 40 50 Figure Time of tirst wave arrival, seconds