ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 345 
earthquake; and all that can be done is to indicate the evidence which points that way, 
and cite certain facts which detract from the force of that evidence and tend to corre- 
late the locally high intensity in the San Joaquin Valley with similar high apparent 
intensities in other valleys thus far discust. 
The apparent intensity on the floor of the Sacramento Valley, as has been stated, 
ranges about VI + of the scale. This is somewhat higher than at several points in the 
adjacent Coast Ranges to the west, and the difference is ascribable to the alluviated 
character of the valley-floor and the water-saturated condition of the alluvium. As we 
follow the Sacramento Valley southward into the San Joaquin Valley, it converges upon 
the San Andreas Rift, and we should naturally expect an increase in the intensity by 
reason of the diminution of the distance from the seat of disturbance. This expecta- 
tion is in a measure realized by an eastward bulge in the isoseismal VII opposite Suisun 
Bay, and by the somewhat higher intensity at Tracy and Westley than at Sacramento 
and Stockton. 
Southward from Westley, however, the apparent intensity increases at a rate which 
can not be referred to the slight approximation of the region to the seat of the main 
disturbance. At Crow’s Landing the apparent intensity is VII; at Newman it is VEE: 
at Volta it is VIII+; and at Los Banos it is IX. These points lie on the west side of 
the valley between the San Joaquin River and the flanks of the Coast Ranges. South 
of Los Banos, on the valley floor, settlements are very few, and information as to the 
apparent intensity is unfortunately lacking over an extensive territory. At Coalinga, 
however, the apparent intensity is VII, indicating that the abnormally high figures 
prevail over the western side of the valley from Crow’s Landing to southward of Coalinga, 
a distance in a north and south direction of not less than 100 miles. That the high 
apparent intensity was not wholly confined to the valley-floor, but also extended into 
the flanks of the Coast Ranges, is shown by the remarkable series of landslides which 
were started by the earthquake for a distance of about 23 miles northwestward from 
the vicinity of Cantua, reported by Mr. §. C. Lillis, and described by Prof. G. D. Louder- 
hack in another part of this report. 
\Now Los Banos, where the apparent intensity was highest, is distant 40 miles from 
tht nearest point on the San Andreas fault at San Juan, its southern end. It is nearly 
34 ‘niles in an air-line from Hollister, the nearest point to the westward having a simi- 
larly high apparent intensity. In the Coast Ranges between Hollister and Los Banos, 
the intensity was as low as V. 
Thise facts are suggestive, as already stated, of a local disturbance at or about the 
se Hn as the main movement along the San Andreas fault. 
Certain circumstances detract, however, from the force of this suggestion, and indicate 
another'possible explanation which, it must be confest, is not very conclusive in view of 
the remcteness of Los Banos from the seat of disturbance. The portion of the San 
Joaquin Valley in which Los Banos lies is undoubtedly an underground water reservoir. 
It lies at the base of the alluvial fans of the Coast Ranges where the streams sink, and 
the waters \f the San Joaquin River maintain the water-table at no great distance below 
the surface.\ As shown by the experiments of Prof. F. J. Rogers, described in another 
part of this teport, water plays an important part under certain conditions in increasing 
the amplituds of the earth vibrations and, therefore, their destructive effect. In this 
respect the region about Los Banos would be particularly favorably conditioned for the 
development & high apparent intensities, as inferred from destructive effects. The 
general conditioys are quite analogous to those in the Salinas Valley, in the bottom-lands 
of the Pajaro River and the Russian River, and in the region about the south end of San 
Francisco Bay. Whe chief difference is in the greater remoteness of the Los Banos region 
from the seat of disturbance, if only one such seat be assumed. 
