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~,. _ <br />i'- ., <br />•' , ; ~ <br />I`~1[CROGEOPHYSICS <br />r-, r:/~`'`,~ CORPORATION <br />... _:~ <br />~/ j <br />" 1 The Deer Creek Canyon area has been subjected to naturally <br />~ occurring ground vibration in the recent past. In 1967, three <br />-'. '+ n.agnitude 5+ earthquakes occurred in northeast Denver. On <br />.. '-' January 5, 1979 a magnitude 3.1 earthquake occurred in Divide, <br />Colorado, t•!aximum particle velocities at the quarry site can <br />^; ~ ~ ire estimated by the equation: <br />-.. J <br />~ -- ~ V = 15 eM (R + 0. ~7 e0.59;d) -1. 7 <br />P;here V = ma::imum grour., velocity (cm/sec) <br />-,~"~~ R = hypocentral distance (km) <br />' ~ ~. ~-'.j And h1 = magnitude <br />r '~ (From Neonnark and Rosenblueti, 1971, 'Fundamentals of Earth- <br />`'- cuake Engineering', Prentice Hail, Inc., Englecaood Cliffs, N.J.) <br />~~:;~-J 'r~ Plaximum particle velocity at Deer Creek Canyon for the 1967 <br />`,+`__ events would have been 1.2 in/sec and for the 1979 event, <br />-.•y _.a " 0.16 in/sec. Therefore, ground notions of the order induced <br />~;~•^;,.`„•n by F7inslow Construction Company quarry shots are part of the <br />-'~~,s"""~ natural environment. <br />- .. , -.,- <br />''q(( Although Winslow Construction Company has not violated ground <br />vibration standards or exceeded naturally occurring particle <br />'~ ~~' __j <br />- ``;~= velocities, ~~ recommend that Winslow Construction Company adopt <br />" delay blasting methods. Use cf delay blasting methods divides <br />Z;;-"`> ~ a production shot into smaller units detonated at 25 millisecond <br />~'~'~ intervals. This small separation in time reduces induced <br />~~;. . <br />.:~,~ ground vibration to that produced by the quantity of explosives <br />,,.. ~" in each delay. Thus, a small change in technique, would reduce <br />~- •. ~-• .~'-p <br />- ` -~ t:>e effects noticed by neighbors and resultant complaints. <br />-~.~ .•.-. ,d <br />P~_ ,,;',raj The report accompanying tY.is letter describes the investigation, <br />''' •~° -,y interpretation and conclusion in detail. <br />.~ 1 <br />'> ,. <br />~ - > - Sincere ~ y, <br />.. ~ <br />~` Q <br />~~ v,~ ~u~ <br />~, '~ ' <br />;.~ "' - Roge Bowman David But er, r. . <br />t•7a .ay-er Registered Geophysicist <br />.~ ~ Engineering Division California No. GP412 <br />~. <br />..' ~ ~~~, JRB/tw , <br />i <br />.~ ~ <br />j X0900 WEST 44TH AL'ENUE / WHEAT RIDGE. COLORADO 80033 ! (303) 424-0499 <br />J <br />