A large number of earthquake hypocenters located at depths of 30 and 100 km may correspond to structures of the order XV, which must be about 1000 km long and up to 300 km wide, according to the morphometric series.
The bibliographic sources (Belousov, 1948 , 1954; Azhgirei, 1959) as well as geological, tectonic, and even physical maps depict these structures as geosynclinal. Among the depressions they include sediment-free forms of the type of deep-sea trenches (Kurile Trench, Marianas Trench, and others), the Black Sea depression, and several other seas, while among mountain structures they include the Greater Caucasus, the Alps, the Carpathians, and many others. The intermontane Tarim depression also probably belongs among analogous structures (according to Fedorovich (1961)) its length is 1100-1410 km, its width 420 km (along the meridian of Keriya), with Meso-Cenozoic strata over 14 km thick; the depth of its basement is still unknown). This depression is in the stage of being filled and bears a special relationship to the surrounding relief, i. e., it is fringed by mountain structures. The significance of these structures in the development of the Earth's crust attracts special attention, and analysis of their morphometric characteristics appears to us to be of extreme interest.
At the present stage it may be noted that the long axis of rectilinear structures of the type of the Greater Caucasus drawn at the depth of 30km under the center of the mountain structure may be regarded as a chord subtending an arc described with a radius of about 6000 km, which is fairly close to the Earth's radius. Since these structures are to a certain extent related to the Earth's dimensions and figure, the other indexes of the entire morphometric series may obey a similar relationship.
In order to examine this possibility, we performed an elementary calculation with the formula where 1 is the full wavelength, equal to twice the index of the width of the relief form in the morphometric series (in the case of a combination of a positive with a negative form), r is the Earth's radius (the equatorial radius of 6378 km was used), IT = 3.14 is the factor necessary for the scaling of linear magnitude to a circle (a sphere).
The results calculated are listed in Table 8. They display an interesting agreement with indexes of the morphometric series.
There is no doubt that this calculation calls for further check and study. Possibly it only indicates the direction in which the solution of the problems of interest to us must be sought.
The patterns discovered suggest that the tectonic structural forms formed in the Earth's crust and reflected on its surface in the relief forms derive from certain general processes occurring in the Earth's body, and that they are proportional to the Earth's dimensions and are dependent upon its physical properties. * Most probably such processes are periodic deformations — oscillations or "waves" generated in the Earth's body by various agents, including solar and lunar attraction, variations in the Earth's rotation about its axis, variations in the atmospheric pressure, etc. The presence of oscillations of various orders in the Earth has already been established by precise instrumental measurements, but their relief-forming significance still calls for painstaking studies. Quite probably, these oscil lations or "waves" are one of the important agents stimulating, regulating, and directing the development of tectonic structures in the Earth's crust. In studies of this problem special attention should be paid to the possible summation of these oscillations and resonance phenomena.
Further studies of the morphometric problems call for additional collection and processing of vast and diversified data, including an enormous amount which are morphometric. These data must be of a higher quality than those heretofore obtained from the literature and from small-scale maps.
Very valuable data are provided by large-scale structural maps compiled by instrumental surveys. Likewise, interesting information can be obtained from studies of fairly accurate maps of the bottom relief of the World Ocean, since the tectonic structures at the bottom of the sea have been less modified by external agents than they have been on dry land. Extremely valuable should be the results of field observations carried out according to a special program.