Chap. 9] 



SEISMIC METHODS 



483 



tion of Young's modulus (or rigidity modulus) the damping tj represents 

 the tangent of a phase angle between elastic (E or y) and dissipative moduli 

 (Uifji and Utu) (see Fig. 9-23). The resulting elastic moduli, E = Eo + 

 jwUi and v = Vo + jwllt , are thus comparable with the apparent dielectric 

 constant (see Chapter 10, page 641). The reciprocal of the tangent of the 



I 



Conditions at Sesonanc* 



Complex Elastic Moduli 



Fig. 9-23. Oscillation of elastic systems represented by complex moduli (after Wegel 



and Walther). 



phase angle has also been designated as "dissipation" constant, although 

 this definition does not appear well chosen, since materials with the 

 greatest energy dissipation would have the smallest dissipation constants. 



III. METHODS OF SEISMIC PROSPECTING 



A. Technique of Shooting; Shot Instant Transmission; Review of 



Seismic Methods 



1. Source of energy: weights, explosives. In seismic exploration dyna- 

 mite is used almost exclusively. However, different energy sources have 



" H. Walther, Bell Lab. Record. 363-366 (Aug., 1934). 



