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elevation using compass , hand level , and measuring tape methods . <br /> Locations and elevations should be considered approximate . <br /> The data reduction and interpretation procedure consisted of <br /> the following sequence of tasks : <br /> o visually picking first breaks of compression waves ( P-waves ) <br /> from the analog records of the oscillograph / seismograph system, <br /> o plotting of time-distance graphs utilizing the raw data , <br /> o preliminary determination of apparent velocities , <br /> o plotting of elevation data along the profiles , <br /> o measurement of differences between act.ual geophone <br /> elevations and a constant -slope profile , <br /> o computer analysis of preliminary apparent velocities and <br /> elevation differences to determine travel —time corrections , <br /> o adjustment of the time-distance graphs and refinement of <br /> apparent velocity determinations satisfying reciprocity , <br /> o comparison of time-distance and velocity data with a catalog <br /> of subsurface structures to interpret an appropriate seismic <br /> refraction model , <br /> o computer analysis ( computer program by Shires , 1983 , <br /> principles published by Mooney , 1977 , Handbook of Engineering <br /> Geophysics , utilizing the condition of reciprocity , travel - time <br /> distance / velocity , and Snell ' s Law of Refraction ) of apparent <br /> velocity and intercept time data to determine depthsof <br /> refractors , true velocities , dips of refractors , and angles of <br /> seismic raypaths , <br /> o measurement of time deviations from "best fit " apparent <br /> velocity slopes on the time-distance graphs , <br /> o computer analysis of apparent velocities and time deviations <br /> to determine refractor profile corrections , <br /> o. adjustment of refractor depths to reflect time deviations , <br /> o correlation of results : with known geologic factors ( from <br /> mapping and borehole logs ) and adjacent or overlapping seismic <br /> refraction data , and _ <br /> o final preparation of interpreted subsurface velocity <br /> profiles . <br /> The equipment used for the seismic refraction survey <br /> consisted of 12 geophones at one time of 4 . 5 Hz natural <br /> frequency . The geophones were connected to 25-foot take-out <br /> spacing cables using Mueller clips . The seismograph used was a 24 <br /> -channel Texas Instruments Explorer 3500 Model . The oscillograph <br />