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Why Earths Poles Never Have Earthquakes?
September 17, 2009 00:24

Earthquakes are powerful natural disaster, which human beings often fail to predict accurately, live alone controlling them. However, scientists all over the world search for some peculiar phenomena, which are associated with earthquakes. They already know, for instance, that Earth’s North and South poles almost never experience an earthquake, while dropping, when moving further towards the equator.

Researchers from the Institute of Marine Geology and Geophysics (Far East Branch of Russian Academy of Sciences), located in Yuzhno-Sakhalinsk, and Moscow Institute of Oceanology (Russian Academy of Sciences), performed a detailed study of patterns, according which earthquakes happen, depending on geographical latitude of a territory. Scientists studied how the amount of this disasters grow towards mid-latitudes, reaching its maximum their and slightly energy of earthquakes was distributed with depths in all latitudes of the Pacific Ocean, where 80% of all earthquakes take place, statistics claims.

The investigation revealed three distinct depth clusters: 10-80, 120-240 and 500-700 kilometers, where 98% of all planet-shaking accidents take place. Scientists discovered an interesting pattern – middle and high latitudes, which were closer to the North and South poles, had earthquakes deep in Earth’s crust very rarely. Moreover, the closer the territory is located to the pole, the narrower the first cluster is (10-20 kilometers instead of 10-80).



In tropical latitudes, 20-30% of earthquake energy is released at medium depths, and 10-12% - at significant depths of 500-700 kilometers. Moreover, in near-equatorial regions deep earthquakes share 40% of all energy released by this phenomenon.

Researchers consider these new tendencies can serve as a basis for future search of the earthquake-generating mechanism. Scientists have come out with several hypotheses why ground-shaking disasters took place mostly in mid-latitudes. The most interesting of them involves tidal forces, which are most powerful at 45th parallels of Northern and Southern Hemispheres. However, the reason why tides have such an effect remains a mystery.

In order to perform the study, scientists processed data about over 200 000 earthquakes, which magnitude was equal or exceeded 4.0 of Richter’s scale. All seismic events were divided into eastern and western ones, and for this purpose 145◦ longitude meridian was used. Western part of the map showed stronger pattern of higher energy release by earthquakes, taking place deep in near-equatorial regions.

Apart from tidal forces, another possible reason for uneven character of earthquakes according to latitude value can be Earth’s rotation, which has different moment of inertia at different latitudes, having the strongest variations in middle latitudes. In other words, in the middle of our planet heterogeneity of its layers at depths between several tens to hundreds of kilometers is the most acute. This fact can be the reason why rotation forces have irregular effect on layers, thus causing occasional seismic disturbances. Source: Science News

Kizilova Anna

Tags: ecology Russian nature    

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