AN ANALYSIS OF THE MEASURED VALUES FOR THE STATE OF STRESS IN THEEARTH'S CRUST

Abstract

The state of stress in the crust of the earth is of great fundamental and practical significance. No totally satisfactory method for measuring the complete state of stress has been devised yet. Despite this, many efforts have been made to measure this state of stress at different locations. From a compilation of many of the results, fifty which yielded the complete state of stress and in which one of the principal stresses is vertical, have been selected for a statistical analysis in an endeavor to define the nature of the state of stress in the crust. These data have been analyzed as a whole, and divided into three groups depending upon whether the vertical stress is the maximum, minimum or intermediate principal stress. Linear regression analyses of the values of half the maximum stress difference as a function of half the sum of the maximum and minimum principal stresses have been made. The correlation coefficients for these fits are 0.786 for the data as a whole and 0.848, 0.790 and 0.383 for each of the groups. Values of the coefficient of sliding friction between blocks of rock comprising the crust, interpreted from the slopes of these lines, ranged from 0.625 (for those measurements where the vertical stress is the maximum principal stress) through 0.427 (for those cases where the vertical stress is the minimum principal stress), to 0.220 (for those cases where vertical stress is the intermediate principal stress). The 98 percent confidence limits for these values lie within +19.4 percent - 16.6 percent.