General regularities in the distribution of seismic events on the Earth and on the Moon

Abstract

In this work, characteristic features of seismic event distribution by latitudes and depth are compared for the Earth and the Moon. It is shown that earthquakes and moonquakes are distributed similarly by latitudi� nal belts. The problem of earthquake epicenter distribution by latitudinal belts of the Earth was stated in the 1960s. Firstly, only the distribution of strong earthquakes ( M > 7) was studied. In the early works [5, 8], hetero� geneity in events distribution by latitudes was noted. A substantial progress was achieved in [9]. On the basis of a Chinese catalogue of strong earthquakes in 1897– 1980 (1165 events), it was noted that the energy released after seismic events is almost zero for high lat� itudes and the two main peaks of seismic activity are located in middle latitudes and are divided by a zone of less activity near the equator. The papers of the authors of the present communi� cation contain the results of the analysis of earthquake latitudinal and depth distributions [2, 3]; however, comparative analysis of earthquake and moonquake distributions taking into account latitude, depth, and energy of events has not yet been undertaken. The aim of the present work is to present the results of such analysis and to comment on the possible relationship of the seismic process with exogenous effects on both the Earth and the Moon. Analysis of a wide spectrum of seismic events was carried out on the material of the ISC catalogue [6] (more than 200 000 events with M ≥ 4) on the basis of the approached elaborated in [2]. It was stated that seismic activity of the planet is almost absent in the poles and in polar caps of the Earth and reveals clearly expressed maximums in middle latitudes of the North� ern and Southern Hemispheres and the stable local minimus near the equator. These distributions by lati� tudinal belts of the Earth are characteristic for a num� ber of seismic events and for released energy as well. Because of the fact that most earthquakes are concen� trated in the boundaries of lithospheric plates, in [2] normalizing of earthquake number and released energy by length of the lithospheric plate boundaries in every single latitudinal belt was used. Such a nor� malizing gives us a power of this area of a plate bound� ary (average number of earthquakes generated per every 100 km of plate boundary). Using of this charac� teristic, the physical sense of which is clear, allows us to compare seismic activity of latitudinal belts in vari� ous parts of the world. The total number of studied events was subdivided into several subgroups by values of magnitude ranges (MRs: 4.0 ≤ Mb < 4.5; 4.5 ≤ Mb < 5.0; 5.0 ≤ M b < 5.5; 5.5 ≤ M b < 6.0; 6.0 ≤ M b ).