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03/17/94 12:13 $303 238 0828 DRC ~ 002/003 <br />Seismic Travel~ime Determination Using Calibration Blasts <br />By setting off small blasts at each surface geophone site (see attached <br />map) and recording the time of arrival of seismic waves at each underground <br />geophone site, we can place constraints on a model of the velocity struc- <br />ture above the coal seam. This seismic velocity model is used to locate <br />seismic events. <br />Each blast will be i/3 to 1/2 of a stick oP powder (we'll use the permissi- <br />ble powder and caps that the Bureau has previously stored in the No. 3 <br />magazine). The powder will be placed at the bottom of an approximately a- <br />foot deep hole produced by driving a steel bar into the groin with a rock- <br />ing action (to produce a slightly conical hole). A contactor will be <br />attached to the geophone cable leading back to the training building (trbq) <br />to provide the exact time of detonation. Depending upon signal quality, we <br />will use one to five blasts at each site. Following the blasts at the <br />first surface geophone site, it will be necessary to determine if the blast <br />waves were recorded on the underground data acquisition system before mw- <br />inq to the next site. After demonstrating the success of recording on the <br />underground system, this manual check of the underground system may not be <br />needed for subsequent blasts at the remaining geophone sites. <br />~~Z ~~ /-S ~~aslz 4~ each v~ 9 STtPS ? ~' S <br />ir~vy.vch Sv~~ R~~r~w„cc P~~G?~a~ ~! ~t~tt M~0 / <br />~,vel 1 ~,.. cl ~~ ta-ce? No, L/-ela-w clef G/c,/~jJ o,~ ~hoi,e C/; ~~ <br />vsht~.~. -1,-~~~; ~ ? ~s~c -b ~..es a.~ve ~~~ We~,.~l.~- ~s y~ / ,~~n/I-F~( <br />wl-.~.. ? rn~ <br />~~ w~ Tcc ~ ~ ~s''// <br />yP wl~~Cq~~ <br />~ ~~~ ~.,~~ 6/~~~,~ - Joy Iv~9~~ <br />t' 7 ~ // <br />-~,yo-~• ~,~,~i~ ~ - ~e lvil/ CGrI~ /LIZ ~(No~2~- USFwS <br /> <br />