Expecting An Earthquake In The Northern Tien Shan

When analyzing Centeral Asia seismicity the researchers noted that powerful earthquakes in the Hindu Kush, Altai and Northern Tien Shan are often grouped by three. Events in the first two regions can happen in the reverse order but the Northern Tien Shan earthquake always accompanies them. Within the last century, five groups of such events took place. The Hindu Kush earthquakes are deep-focus ones, they take place at the depths of 100 to 230 kilometers, in contrast to others, more shallow ones in the interior of the earth’s crust. It may take from 1.8 to 6.9 years from the first through the third earthquake in the group of three, while the interval between the second and the third earthquake makes up 20 days to a year and a half.

According to the researchers’ calculations, probability is rather high that within 100 years it was by chance that the pairs consisting of the Hindu Kush and the Altai earthquakes were formed for five times, but it is no way that groups of three earthquakes could accidentally happen for five times. Probability of such event makes about one of the hundred thousandth. Apparently, a group of three occurs as follows: first the Hindu Kush and the Altai earthquakes happen (in any succession but at the interval not exceeding six years), after which likelihood abruptly grows that a cataclysm will also take place in the region of the Northern Tien Shan within the next year and a half.

Why does the Northern Tien Shan regularly respond to the events that took place in the Hindu Kush and the Altai? According to the specialists’ opinion, the main reason is as follows. The lithosphere of the vast regions in Central Asia from the Hindu Kush and the Western Himalayas through the Altai and the Sayan Mountains is under the action of stresses caused by collision of the Indian and the Eurasian platforms. The stress field in the region is relatively homogeneous. After a pair of powerful earthquakes in the regions of the Hindu Kush and the Altai, the stresses redistribute, and as a result pressure increases between seismic event foci. The stresses should increase most of all exactly in the middle between them, just where seismic foci of powerful earthquakes of the Northern Tien Shan are located. Their energy is usually significantly lower than that of the first two events in the group of three, thus confirming the hypothesis of the Russian and Kazakhstan researchers.

The last group of three earthquakes that took place in 2002-2003 differs to some extent from the previous ones, mainly because after it, on October 8, 2005, there occurred one more very powerful crustal earthquake with seismic magnitude of 7.6 in the area of Kashmir, nearby the Hindu Kush zone. This was the most powerful earthquake for the last one hundred years within a radius of 600 kilometers from this zone. According to the specialists, this earthquake’s effect should be similar to the effect of the deep-focus Hindu Kush events. The researchers assume that there may happen one more event in the region of the Northern Tien Shan (its magnitude being about 6 and more) after a group of the 2002-2005 powerful earthquakes. The most probable time of the disaster is a year and a half after the Kashmir earthquake, that is approximately through April 2007. One of likely locations for this earthquake preparation is the region of the Kirghiz mountain ridge to the south-east of Bishkek. In 2004, two rather powerful deep events already took place there, which can be considered as forerunners of the impending cataclysm.

“By the way, an earthquake already happened in the mentioned region on December 25 last year, says Yuri Kopnichev, its magnitude being 5.8, which is practically in line with our forecast. It caused major destruction in Kochkor region of Kirghizia. Nevertheless, we expect that a more powerful event is to occur here.”