Calculated gravity anomaly produced by possible fault under line 27-48

Abstract

The seismograph data from Line 27-48 of Party 47 indicates the possibility of a high angle fault win a displacement of roughly 1,000 feet under South Barrow Test Well No. 2. This fault vas discussed in E. Wiancko's report for United Geophysical Company entitled "Report of Reflection Seismograph Survey in the Barrow Area During 1948". Mr. Delta. and Mr. English recently expressed a desire to know the magnitude of the calculated gravity anomaly produced by this probable fault. Their purpose was to determine the feasibility of proving and locating this fault, if exists, by several traverses with the gravimeter. As interpreted in Wiancko's report, the fault is nearly east-west in strike and is a reverse fault with the up-thrust block on the north side. The assumptions made for the calculation of the theoretical anomaly were that the density of the basement rock was 2.7, the density of the overlying rocks was 2.2 and the fault itself was taken directly from Plate I, Drawing No. 2044, of Wiancko's report, simplified, and reduced by a factor of 2. The calculated anomaly is shown in Fig. 1. A polar chart similar to the type described on pages 153-154 of Heiland's "Geophysical Exploration" was used in computing the value of the anomaly. It was assumed that the feature is two-dimensional. Broken lines indicate values of limited accuracy. It should be mentioned here that Mr. Roland Henderson and Mr. Isidore Zietz of the Section of Geophysics of the Geological Survey carried out the calculations and plotted Fig. 1.