226 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 














Rossi-ForeEuL OmoRI SAN FRANCISCO ACCELERATION 
SCALE. SCALE. SCALE. mm. PER SEC. PER SEC. 
No. 7 
— 4,000 _ 
Grade A 
No. 6 
— 3,000 - 
E 2,500 — 
10 No. 5 
Grade B 
senteitees 1 ee a 1 2POOu) SS 
9 No. 4 
; — {900 aS 
No. 3 ; 
Grade C a 900 ie 
8 — S00. 
2 
Grade D 
———~ — 300 _ 
y No. 1 A 200 ie 
Grade E 
It may be perhaps well to point out that Grade D lies between Nos. VIT and VIII of 
the Rossi-Forel scale. This grade characterizes the greater part of the city, as the in- 
tensity map shows. Grade B, equivalent to Nos. LX and X of the same scale, is character- 
istic of very small areas only. Grade A is not exhibited in the city proper. 
Utilizing the San Francisco scale, intensity map No. 19 was prepared, which indicates 
the location and areal extent of the districts characterized by each grade of intensity. 
It presents graphically the results of the field work. In the field study, practically all of 
the city proper, including the large area devastated by fire, was thoroly traversed, ex- 
cepting one or two isolated hilly localities where a brief examination showed no significant 
damage. Unbuilt districts were, of course, comparatively neglected, except where dis- 
turbances of natural objects were found or lookt for. Chimneys, buildings, streets, 
paving, curbing, sidewalks, car tracks, retaining walls, etc., were subjected to careful 
scrutiny, and such injuries as were observed were classified on the spot in terms of the San 
Francisco scale. The intensity indicated was recorded by a spot of color placed upon a 
field map of suitable scale (1,760 feet to the inch, or 1: 21,120). Many photographs 
were made, some of which appear as illustrations in this report. 
Detailed field notes were made only when damage of unusual or striking character was 
encountered, or when it was perplexing. When effects were observed which seemed 
likely to be of value in analyzing the character of the earth motion, notes were made. 
Little indoor evidence was obtained or sought. 
It will thus be seen that the field study, while adequate for the purposes in view, did not 
constitute an expert engineering investigation, dealing with specific details and location 
of damage. Frequently there was doubt as to what grade of intensity should be assigned 
to a given city block, because of conflicting or inadequate evidence in the field. This is 
particularly true of districts swept by fire, especially where the intensity was low; for most 
