Regional Tectonic Subdivisions According to Depth

Abstract

In approaching the problem of making a regional tectonic subdivision according to depth (I think it is already clear to the reader that by “depth” we primarily mean the subcrustal zone), we find it possible in practice to use only data for deep-focus earthquakes. The one-sidedness of this information, its obvious incompleteness is the result of inadequate study. To a certain degree the information is random, the result of our lack of information concerning the distribution and change of intensity in frequency of earthquakes of the past. Lastly, we lack knowledge of what quantitative characteristics define in nature delimiting types of regions. It would appear that all these deficiencies compel us to reject any simple regional classification according to intensities of seismic activity. A more fundamental approach would be to distinguish regions according to qualitative change in seismicity with depth. This would essentially lead us to a subdivision of regions according to focal depth of earthquakes. In this case, we distinguish regions according to presence or absence of earthquakes at particular depth intervals. The intervals themselves are determined by composite geologic and, in part, geophysical data.