520 



SEISMIC METHODS 



[Chap. 9 



Fig. 9-58. Reverse travel-time curve for deep- 

 seated escarpment. 



the travel-time curve from a 

 straight Une. Where it is 

 nearly enough parallel with 

 the ^2 curve, the time differ- 

 ence A^ may be determined 

 and is again approximately 

 proportional to the displace- 

 ment di — di . Fig. 9-59 is 

 an example of the determina- 

 tion of depth of overburden 

 and displacement of a fault at 

 the same time. The first part 

 of the profiles shown are at 

 right angles to a fault, and 

 the second part (profile D) is 

 in the strike of a fault, which 

 had been located by torsion 

 balance observations and by 

 wells. Faults are of commer- 



cial importance in this area, as the occurrence of hematite ore in the lime- 

 stone is associated with the faults. In this case the seismic problem was 



South 



Fig. 9-59. Seismic refraction profiles, hematite district, Millom, Cumberland, England 



(after Shaw). 



