GEOPHYSICAL METHODS OF INVESTIGATING 



241 



is crooked the time will vary accordingly. The time taken 

 by the wave in traveling to the geophone will give the length 

 of its path when we know the vertical velocity of the local 

 formations by the above or similar computations (Mr. 

 Malamphy simplifies these computations drastically), since 



Fig. 161. — (a) Plan sketch showing ideal location of shot points for deter- 

 mining deviation of hole from vertical. H' indicates the position on the surface 

 directly above the point at which the detector is placed in the hole. This point 

 is determined by arcs from the various shot points. (6) Vertical section along 

 line E W showing crooked drill hole and path of the seismic waves to the detector, 

 (c) Vertical section showing method of shooting profile to determine true depth 

 and average vertical velocity. {After M. C. Malamphy.) 



the depth of the apparatus in the hole is known direct 

 (Fig. 161). The time taken by the shot wave from W 

 will be less than that from E (Fig. 161&) if the hole is 

 crooked. Knowing the depth and vertical path we may 

 get the other side of the triangle and thus the distance 

 from H' to E and to W; the point H' being on the surface 



