4 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
bottoms that the vibratory movement due to the passage of the earth-wave was 
characterized by greater energy than where it traversed elastic rocks; but that this 
energy was manifested in a form of movement more destructive to structures upon 
the surface. The intensity of the shock upon the valley-bottoms, as inferred from 
damage, seemed abnormally high. In terms of energy it was probably not abnormal. 
It thus became necessary to discriminate between apparent intensity and real intensity. 
Inasmuch as we have to deal primarily with observable effects and record these as 
a basis for inference, it has been found convenient to use the term “apparent inten- 
sity”? in a technical sense thruout the report; and all the grades of intensity specified, 
even when the qualification ‘‘apparent”’ is omitted because of the wearisomeness of its 
reiteration, are grades of “apparent intensity” arrived at by applying literally the 
criteria of the Rossi-Forel scale. 
