BIMODAL LATITUDINAL DISTRIBUTIONS OF THE EQ HYPOCENTERS IN THE PACIFIC: GENERAL TENDENCIES

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The statistically valid regularity of the EQ distribution in the Pacific over latitudinal belts and over the depth
was discussed. The worldwide catalog ISC was used. The entire set of events (with Mb>=4.0) was divided into
several magnitude ranges (MR). The regions under study were divided in several latitudinal intervals (belts).
The latitude distributions of the EQ number and energy released by EQ were analyzed. The number of events
in each latitudinal interval was normalized two times. Thus we obtain relative seismic event number generated
per one kilometer of the plate boundary. Double normalized latitudinal distributions have clearly expressed
bimodal character: two peaks located in Northern and Southern Hemisphere, local minimum near the equator
and almost zero values in high latitudes. It was proved the stability of obtained results to different time interval
and to different size of the latitudinal belts. The analysis of 2D EQ distributions (in depth and in latitudinal
belts) was also fulfilled. It was shown, that full interval of depth in each latitudinal belt generally divides into
three parts (clusters) with close-cut separation boundaries (К1 – with 0<H≤80 km, К2 with 120<H≤240 km
и К3 with H≥500 km). The analysis of the obtained EQ latitudinal distributions shows, that the difference in
the EQ number between some latitudinal belts is more than several tens times and for energy distributions this
difference is more than 100 times. At the same time the maximum difference in the plate traveling velocities in
subduction zones is no more than 10% (for example the Pacific part of the South America from 50 N to 450 S).
It seems that it difficult to explain these peculiarities of the latitudinal distributions only from point of view
the theory of plate tectonics. It was discussed the possible linkage between the seismic process and tidal forces.
The strongly pronounced irregularity of EQ latitudinal distributions can find the explanation in future only as
a complex problem by joint analysis of the geological effects, influence of tectonic forces, tidal forces and the
Earth rotation.