Laserfiche WebLink
Mr, pale Ream <br />Cooley Gravel Co, <br />July 10, 1972 <br />Pae'e 5 <br /> <br />The second shot, June 17, 1972, was recorded on the property of Rufus <br />Johnson, the closest continuously used human habitation, Mr, Dale <br />Ream of the Cooley Gravel Company reported that this shot consisted <br />of 209 sacks of AFNQ in 108 holes each 40 feet deep. <br />The site was in a road cut on firm, undisturbed fill, probably less than <br />10 feet thick. Instruments used were an accelerometer, a velocity- <br />sensing short-period seismometer, and a recording sound-level meter. <br />The short-period vertical seismometer functioned well but details of the <br />ground motion were lost due to an insufficient ink supply to the pen. This <br />problem did not prevent the recovery of the maximum velocity and dom- <br />inant frequency of ground motion recorded by this instrument, The read- <br />. ings are summarized in Table 2, Maximum vertical ground motion <br />recorded was less than 0.07 inch/second. <br />The RFT-250 accelerometer was set up near the same spot, Figure 3 <br />is a 4X enlargement of the accelerometer record. Analysis of the data <br />is shown in Table 3, This record shows a vertical equivalent velocity of <br />0.08 inch/second, and a maximum ground velocity equivalent of 0, 11 <br />inch second. <br />7'he signal of the sound-level meter was lost at the time of the shot, due <br />to an upsurge of local wind noise at the input microphone. Ambient noise <br />levels in the general area were recorded, including a decelerating diesel <br />ti^uck which reached a sound level of 90 db, <br />Only an expert structural engineer could evaluate the effects of similar <br />g:^ound motions on specific structures. For information purposes only, <br />we have included Figure 4 which shows the probable effects of these mo- <br />ti~ns on structures. The maximum recording From the second shot is <br />marked on that graph. The U. S. Bureau of Mines also divides the <br />arnplitudes of ground motions into two zones, a "safe" zone and a "damage" <br />zone. The dividing line is 2, 0 inches second, about 20 times greater than <br />the maximum ground velocities measured at this site. <br />~i <br />i <br />