FAULTS 



8lT 



"The fault strike is the direction of the intersection of the fault 

 surface, or the shear zone, with a horizontal plane." The same pre- 

 cautions apply here as in the case of the strike of the strata on a 

 sloping- hillside. (See p. 800.) The term "trend"' would be bet- 

 ter and would avoid confusion. 



"The fault dip is the inclination of the fault surface, or shear 

 zone, measured from a horizontal plane. It is never greater than 



90°.; 



"The hade is the inclination of the fault surface or shear zone, 

 measured from the vertical ; it is the complement of the dip." Hade 

 is to be preferred to dip to avoid confusion with dip of strata. (See 

 beyond.) 



"The hanging zvall is the upper wall of the fault." It generally 

 overhangs the vertical. 



"The foot wall is the lower wall of the fault." It generally pro- 

 jects footwise at the base. 



Fig. 193a. A horse. 



In stratified rocks faults may be parallel in strike to the strike of 

 the strata, when they are called strike faults, or the strike may be 

 approximately at right angles to the strike of the strata, when they 

 are called dip-faults. The bedding fault is a special type of strike 

 fault, in which the fault plane and bedding plane coincide. Be- 

 tween the strike faults and the dip faults are many directions giving 

 oblique faults. When the genera*l structure of a region is consid- 

 ered, the faults may be called longitudinal, when their strike (or 

 trend) is parallel to this structure, or transverse, when it is across 

 the structure. 



The slip of a fault is the displacement on the fault surface. The 

 net slip is the actual amount of movement between points on the 

 opposite walls originally in contact. The strike"^- slip (trend-slip) 



* Strike and dip here refer to the strike and dip of the fault, not of the strata. 

 Trend and hade would be better. 



