172 



HELD ET AL. REPORT ON NOMENCLATURE OF FAULT: 



the perpendicular, or shortest, distance, measured on the fault plane, be- 

 tween the two parts of a dislocated bed, vein, or other surface; bd in 

 figure 2. 15 The trace-slip and the perpendicular slip are rectangular 

 components of the net slip. 



SHIFT 



It frequently happens that a fault has not a single surface of shear. 

 but consists of a series of small slips on closely spaced surfaces, and in 

 some faults the strata in the neighborhood of the fault surface are bent. 

 so that the relative displacements of the rock masses on opposite sides 

 of the fault may be quite different from the slip and not even parallel 

 with it. The word "shift" is used to denote the relative displacements 

 of the rock masses situated outside the zone of dislocation : the qualifying 



Figuee 4. — The Shift 



words relate to the strike and dip of the fault with one exception, in 

 which the meaning is clear. 



The shift, or net shift, denotes the maximum relative displacement of 

 points on opposite sides of the fault and far enough from it to be outside 

 the dislocated zone: de in figures 3 and -i. where d is the position of a 

 selected point before and e after the faulting. 



The strike-shift is the component of the shift parallel with the fault- 

 strike ; df in figures 3 and 4. 



The dip-shift is the component of the shift parallel with the fault dip; 



Spurr calls this the '"lateral separation. 



