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I':' <br />2-2 <br />• A trial earth model was developed by examining geophysical logs <br />~.. of [he exploration holes and discussing the general geology of the area <br />with Coors personnel. Several theoretical field curves were calculated <br />from the trial earth model using RESIST, a computer program developed by <br />r Phillip A. Davie (1979). Davis' program utilizes linear filter theory to <br />solve the forward problem. The theoretical field curve is compared with <br />I the observed field curve and then modified to reflect the observed field <br />data curve. To perform [he final two steps, Ertec used INVERSE, another <br />code developed by Davis (1979). The inversion is accomplished using <br />Marquardt'e algorithm. Theoretical field values and observed field <br />values are compared and modified by the code until the difference in <br />values Ealls below a specified root mean square error. <br />In truth, there ie only one theoretical geoelectric model that <br />will exactly fit the observed field data. Accepting some limit of error <br />l and realizing [he range of possible solutions is constrained by the <br />l existing geology, we can develop a plausible ewdel to match the field <br />f • data observed. <br />L. <br />_~ After a satisfactory fit was achieved, which we assumed to be <br />a root mean square error of 10 or less, the depth to the claybedrock <br />interface was subtracted from the elevations surveyed by Coors person- <br />nel. These values were then used to produce a structural contour <br />map of the apparent bedrock surface top. <br />Geologic cross-sections were prepared for line 1 through line 6 <br />(Figures 2 - 7). Because of the short length of Line 7 and the question- <br />able data collected along the line, a cross-eection was not prepared. <br />Analysis of all data was straightforward and fairly uncomplicated. <br />Approximately 20 different models with varying layer thicknesses and <br />resiativities were needed because of the lateral nonhomogeneity of the <br />geology. Forty-five of the forty-nine soundings were modeled with root <br />mean square errors of leas than five. The remaining four were modeled <br />~ • <br />