
| 
rh 
rH 
fl 
@ 
A 
[| 
Ete 
ies 


pec is 72 f 
(iL Se SeS |S 
ary Esse -_— 
ee a DETECTOR 
[ei eg SSRI ENE 7 Sel 
EES ay ay aoe Sy ae as eS == D3 
DER ier mer ae a OY 
RES a SS Sa | 5 
SE) ew Garay Ks ae 9 ame z 
ES eS Cea as De _ SS eee 
CELL = = = =e === = 
Fic. 4.—-Diagram showing use of well for determining position of fault plane at 
different depths. Patent applied for. 
also determines, with sufficient accuracy for all practical purposes, the 
extent of the mushroom condition. ‘This can be done by the method 
previously outlined only in a zone immediately adjoining a well being 
used for the test. It is possible, however, by an extension of this method, 
to determine definitely the existence of mushrooming on a wide zone on 
the opposite side of the dome from that on which the well is located. The 
procedure is illustrated in Figure 5. Here the detector is placed at any 
suitable depth in the well and a shot is fired 4 or 5 miles away from 
the dome on the same side of the dome as the well. This shot point 
is designated as Shot Point 1 in Figure 5, its direction being indicated 
by the arrow. When the shot is several miles away from the dome, 
experience has shown that under these conditions the wave front, instead 
of being spherical, becomes somewhat ellipsoidal, the deeper parts of the 
wave front being far in advance of the shallower parts, as shown by the 
curved line representing such a wave front in Figure 5. Because of this 
bulging of the wave front with increasing depth, that part of the wave 
front which first reaches the detector at D, is far in advance of the posi- 
tion of the same wave front which reaches a series of detectors on the 
surface at D,, D,, D,. If the detectors at all four of these positions be 
connected with a recorder, the amount of advance of the deeper parts 
of the wave front in excess of the surface part can be recorded accurately 
on a film. 
Another shot is next placed at Shot Point 2 on the opposite side of 
the dome, and a detector, D,, also is placed on the surface at a suitable 
point approximately symmetrical with respect to D,; in relation to the 
124 
