238 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
sion effects, however, are believed to be due to the same cause as that which generated 
the wave forms; for there is no evidence of any true shortening, or lengthening, of the 
north-south dimension of this district, nor is there any probability of this having occurred. 
In addition, then, to the flow movement and the settling together of the loose materials 
causing depression, there was some sort of rhythmic movement in this loose earth which 
produced wave forms in the surface, with places of compression and places of stretching. 
It probably was this movement which was most effective in producing structural damage. 
It is not believed that these surface waves were traveling waves “frozen” as the shock 
subsided. If they had been of that character, the ground surface should be more broken 
than it appeared to be; for in relatively rigid materials such waves must develop open 
fissures along the crests, which would close with crushing in the troughs. It must be 
noted, without any attempt at explanation, that the destructive effects of great magni- 
tude which have been described above, are practically confined to the ‘‘made”’ land which 
occupies the old marsh site. 
Southeast of Brannan Street, where formerly lay Mission Bay, such effects are of less 
magnitude, in general; are less regular in their occurrence and are, on the whole, less 
prevalent. The complete devastation caused by the fire in this neighborhood leaves 
little to indicate the actual damage to the buildings wrought by the earthquake. Certain 
hotels or apartment houses are known to have collapsed, and many fatalities must have 
occurred. Probably a few dwellings were thrown down. A fairly large percentage of 
the buildings, one must believe, were rendered dangerous for occupation, even tho not 
completely thrown down. 
The new United States Post-office building (plate 948), at the corner of Seventh and 
Mission Streets, was just on the margin of the district. It is a steel and granite struc- 
ture, resting upon a foundation of piling driven to a considerable depth, but not as far 
as some had considered advisable. At its southwest corner, the streets are deformed 
into great waves, some with an amplitude of at least 3 feet, causing fissures and sharp 
compressional arches in the pavement and sidewalks. Some of the granite flanking 
structures, which did not rest upon the pile foundation of the building, shared this 
undulatory movement. In consequence, the building appears badly damaged to the 
casual observer. It is quite true that the structure was terribly shaken and greatly 
damaged — such injuries as the destruction of mosaics in the arches of the corridor 
helped to increase the loss — but the structure was not in peril of collapse, tho one of 
the low walls had to be supported by timbers. For the most part, the building survived 
the ordeal, and is in a safe condition for use. 
As stated briefly above, a similar district of high intensity occurs in an area of made 
land along the lower portion of the former course of Mission Creek. ‘This district varies in 
width from 1 to 2 blocks, extending from near the corner of Ninth and Brannan Streets 
westward for about 3 blocks, then southwestward for about 2 blocks more; and finally, 
westward some 4 blocks more to a point on Nineteenth Street just east of Dolores Street. 
Mission Creek was formerly a sinuous tidal stream, with narrow fringes of salt marsh 
about its banks. Near its mouth the stream wound around a rocky point where the 
serpentine hills of the Potrero rose abruptly from its southern bank. Here, along its 
margin, is found the most sudden transition from high to low intensity that is anywhere 
encountered in the city. Along Dore Street, a narrow alley running from Bryant Strect 
to Brannan Street, between Ninth and Tenth Streets, the street pavement was broken 
into a series of waves. The photographs, plate 89p, looking along Dore Street from 
Bryant toward Brannan Street; plate 90a, looking from Brannan Street in the reverse 
direction; and plate 908, showing in detail the trough of one of these waves, with the 
fissuring of the pavement near the farther crest, indicate more clearly than words the 
great intensity manifested here. Less than 2 blocks south on the hill slopes, more than 
