Stressed state in the southeastern part of the German democratic republic based on field investigations and data on contemporary crustal movements

Abstract

A comparison between the results of stress measurements in underground conditions and geophysical data and a analysis of contemporary crustal movements show that there is a direct relation between the measured stress fields and the long-term movements of the crust recorded at the surface. The results of an analysis of the crustal movements agree with the measured stresses within the measurement error. Recent measurements of the stress state in underground conditions are receiving geological and tectonic interpretations with greater frequency. In most cases it is found that the stress state differs from the usual ideas of lithostatic pressure increase. In large regions (and over long intermediate times) there are relatively constant stress fields which may have local deviations. In conformity with the geological structure of the investigated region of the GDR, we can distinguish zones with similar movement behavior and obviously constant stress states in space. Only by comparing the stress state and the contemporary crustal movements can we estimate the validity and utility of the measurements of the principal stress state of a given region. Furthermore, quantitative estimates can be made of the required number of stress measurements and the best sites for them. The relations revealed here are of practical importance for the efficiency and safety of mining operations. The value of reliable and precise information concerning the stress state of the rocks in estimating the stability of underground workings and pillars is obvious. The question of the distribution of point determination of the stresses in areas and regions remains largely avoidable or solvable only by means of very costly experiments. The results show that even at relatively great distances we can regards the principal stress state as constant provided that we do not go outside the established block boundaries. Otherwise, even at short distances from the measurement site we can observe marked changes in the stress states of the rocks. Under certain circumstances we can explain variability in the behavior of the rock massif for which sufficient reasons would appear to be lacking. Analysis of this type enable us to reliably recognize particularly dangerous situations in mining practice, which may be associated with additional loads due to certain human activities and closely related to the geological structure of a certain territory. In the GDR we are taking steps to make a comparative analysis of the stress states of the rocks and the contemporary crustal movements for all the mining areas.